Flight Management System (FMS) Software and its Relationship with LNAV and VNAV

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OEM 737 CDU page displaying the U version of software used by the Flight Management Computer.  The page also displays the current NavData version installed in addition to other information

The procedure to takeoff in a Boeing 737 is a relatively straightforward process, however, the use of automation, in particular pitch and roll modes (Lateral and Vertical Navigation), when to engage it, and what to expect once it has been selected, can befuddle new flyers.  

In this article I will explain some of the differences between versions of software used in the Flight Management System (FMS) and how its relates to Lateral and vertical Navigation (LNAV  & VNAV). 

It’s assumed the reader has a relatively good understanding of the use of LNAV and VNAV, how to engage this functionality, and how they can be used together or independently of each other.

FMS Software Versions

There are a several versions of software used in the FMC; which version is installed is dependent upon the airline, and it’s not unusual for airframes to have different versions of software.

The nomenclature for the FMC software is a letter U followed by the version number.  The version of software dictates, amongst other things, the level of automation available.  For the most part, 737 Next Generation airframes will be installed with version U10.6, U10.7 or later.

Boeing released U1 in 1984 and the latest version, used in the 737 Max is U13.

Later versions of FMC software enable greater functionality and a higher level of automation – especially in relation to LNAV and VNAV.

Differences in Simulation Software

The FMS software used by the main avionics suites (Sim Avionics, Project Magenta, PMDG and ProSim-AR) should be identical in functionality if they simulate the same FMS U number.  

As at 2018, ProSim-AR uses U10.8A and Sim Avionics use a hybrid of U10.8, which is primarily U10.8 with some other features taken from U11 and U12.  Precision Manuals Development Group (PMDG) uses U10.8A.  

Therefore, as ProSim-AR and PMDG both use U10.8A, it’s fair to say that everything functional in PMDG should also be operational in ProSim737.  Unfortunately, as of writing, PMDG is the only software that replicates U10.8A with 97+-% success rate.

To check which version is being used by the FMC, press INIT REF/INDEX/IDENT in the CDU.  

Writing about the differences between FMC U version can become confusing.   Therefore, to minimise misunderstanding and increase readability, I have set out the information for VNAV and LNAV using the FMC U number.   

Roll Mode (LNAV)

U10.6 and earlier

(i)    LNAV will not engage below 400 AGL;

(ii)    LNAV cannot be armed prior to takeoff; and,

(iii)    LNAV should only be engaged  when climb is stabilised, but after passing through 400 feet AGL.

U10.7 and later

(i)    If LNAV is selected or armed prior to takeoff, LNAV guidance will become active at 50 feet AGL as long as the active leg in the FMC is within 3 NM and 5 degrees of the runway heading.  

(i)    If the departure procedure or route does not begin at the end of the runway, it’s recommended to use HDG SEL (when above 400 feet AGL) to intercept the desired track for LNAV capture;

(ii)    When an immediate turn after takeoff is necessary, the desired heading should be preset in the MCP prior to takeoff;  and,

(iii)    If the departure procedure is not part of the active flight plan, HDG SEL or VOR LOC should be used until the aircraft is within range of the flight plan track (see (i) above).

Important Point:

•    LNAV (U10.7 and later) can only be armed if the FMC has an active flight plan.

Pitch Mode (VNAV)

U10.7 and earlier

(i)    At Acceleration Height (AH), lower the aircraft’s nose to increase airspeed to flaps UP manoeuvre speed;

(ii)    At Thrust Reduction Altitude (800 - 1500 feet), select or verify that the climb thrust has been set (usually V2+15 or V2+20);

(iii)    Retract flaps as per the Flaps Retraction Schedule (FRS); and,

(iv)    Select VNAV or climb speed in the MCP speed window only after flaps and slats have been retracted.

Important Points:

  • VNAV cannot be armed prior to takeoff.

  • Remember that prior to selecting VNAV, flaps should be retracted, because VNAV does not provide overspeed protection for the leading edge devices when using U10.7 or earlier.

U10.8 and later 

(i)    VNAV can be engaged at anytime because VNAV in U10.8 provides overspeed protection for the leading edge devices;

(ii)    If VNAV is armed prior to takeoff, the Auto Flight Direction System (AFDS) remains in VNAV when the autopilot is engaged.  However, if another pitch mode is selected, the AFDS will remain in that mode;

(iii)    When VNAV is armed prior to takeoff, it will engage automatically at 400 feet.  With VNAV engaged, acceleration and climb out speed is computed by the FMC software and controlled by the AFDS; and,

(iv)    The Flaps should be retracted as per the flaps retraction schedule;

(v)    If VNAV is not armed prior to takeoff, at Acceleration Height set the command speed to the flaps UP manoeuvre speed; and,

(vi)    If VNAV is not armed prior to takeoff, at Acceleration Height set the command speed to the flaps UP manoeuvre speed.

Important Points:

  • VNAV can be armed prior to takeoff or at anytime.

  • At thrust reduction altitude, verify that climb thrust is set at the point selected on the takeoff reference page in the CDU.  If the thrust reference does not change automatically, climb thrust should be manually selected.

  • Although the VNAV profile and acceleration schedule is compatible with most planned departures, it’s prudent to cross check the EICAS display to ensure the display changes from takeoff (TO) to climb or reduced climb (R-CLB).  

Auto Flight Direction System (AFDS) – Operation During Takeoff and Climb

U10.7 and earlier

If the autopilot is engaged prior to the selection of VNAV:

(i)    The AFDS will revert to LVL CHG;

(ii)    The pitch mode displayed on the Flight Mode Annunciator (FMA) will change from TOGA to MCP SPD; and,

(iii)    If a pitch mode other than TOGA is selected after the autopilot is engaged, the AFDS will remain in that mode.

U10.8 and later

(i)    If VAV is armed for takeoff, the AFDS remains in VNAV when the autopilot is engaged; and,   

(ii)    If a pitch mode other than VNAV is selected, the AFDS will remain in that mode.

Preparing for Failure

LNAV and VNAV have their shortcomings, both in the real and simulated environments.

To help counteract any failure, it’s good airmanship to set the heading mode (HDG) on the MCP to indicate the bearing that the aircraft will be flying.  Doing this ensures that, should LNAV fail, the HDG button can be quickly engaged with minimal time delay; thereby, minimising any deviation from the aircraft’s course.

Final Call

I realise that some readers, who only wish to learn the most recent software, will not be interested in much of the content of this article.  Notwithstanding this, I am sure many will have discovered something they may have been forgotten or overlooked.

The content of this short article came out of a discussion on a pilot’s forum.  If there is doubt, always consult the Flight Crew Training Manual (FCTM) which provides information specific to the software version used at that particular airline.

Glossary

  • CDU – Computer Display Unit.

  • EFIS – Electronic Flight Instrument System.

  • FMA – Flight Mode Annunciator.

  • FMC – Flight Management Computer.

  • FMS - Flight Management System.

  • LVL CHG – Level Change.

  • LNAV – Lateral Navigation.

  • MCP – Mode Control Panel.

  • ND – Navigation Display.

  • PFD – Primary Flight Display


  • VNAV – Vertical Navigation.

ISFD Knob Fabricated

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OEM ISFD (Image copyright Driven Technologies INC)

The Integrated Standby Flight Display (ISFD) is mounted in the stand-by instrument cluster in the Main Instrument Panel (MIP).  The ISFD provides redundancy should the Primary Flight Display (PFD) on the Captain or First Officer fail. 

The ISFD is not a common panel to find second hand, and working units are expensive to purchase.  I don't  have an OEM ISFD, but rather (at least for the moment) use a working virtual image displayed by ProSim737. 

ISFD knob.  Two versions: one replicates the taller NG style while the other is slightly shorter.  Although not functional, they provide a better representation of the plastic knob that previously was installed

Conversion of an OEM unit is possible, however, the unit would need to be fully operational, and  finding a working unit at a reasonable price is unlikely.  ISFDs are expensive and reuse is common.  If a unit does not meet certification standard, it's disposed of because it's broken and cannot be economically repaired.

ISFD Knob

The ISFD knob that came bundled with the MIP I purchased is very mediocre in appearance – in fact it's a piece of plastic that barely looks like a realistic knob.  I purposely have not included an image, as the design would be an embarrassment to the company that produced the MIP.

A friend of mine is a bit of a wizard in making weird things, so I asked him if he could make a knob for me.  He made two knobs – one based on the standard design seen in the Next Generation airframe and the other knob a shorter version of the same type. 

Knob being fabricated on a lathe

Attention to Detail

Attention to detail is important and each knob has the small grub screw and cross hatch design as seen on the OEM knob.  The knobs have been made from aluminum and will be primed and painted the correct colour in the near future.

A 2 axis CNC lathe was used to fabricate the knobs.  The use of a computer lathe enables the measurements of a real knob to be accurately duplicated, in addition to any design characteristic, such as cross hatching or holes to install grub screws.

Wind Correction (WIND CORR) Function - CDU

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OEM 737 CDU showing WIND CORR display in Approach Ref page

Wind Correction (WIND CORR)

The approach page in the CDU has a field named WIND CORR (Wind Correction Field or WCF). 

WIND CORR can be used by a flight crew to alter the Vref + speed (speed additive) that is used by the autothrottle during the final approach.   This is to take into account wind gusts and headwind that is greater than 5 knots. 

Changing the Wind Correction to match increased headwind and gusts increases the safety margin that the autothrottle operates, and ensures that the autothrottle command a speed is not at Vref.

WIND CORR Explained

The algorithm of the autothottle includes a component that includes a speed additive.  The speed additive is 1.23 times greater than the stall speed of the aircraft (at whatever flap setting).  When the autothrottle is engaged, the speed additive is automatically added to Vref.   This provides a safety buffer to ensure that the autothrottle does not command a speed equal to or lower than Vref. This added speed is usually 'bled off' during the flare ensuring landing is at Vref.

Although the autothrottle algorithm is a sophisticated piece of software, there is a time lag between when the sensors register a change in airspeed to when the physcial engines increase or decrease their spool (power).   By having a speed additive (based on headwind and gust component) the speed of the aircraft (as commanded by the autothrottle) should not fall below Vref.

A Vref+ speed higher than +5 can be inputted when gusty or headwind conditions are above what are considered normal.  By increasing the additive speed (+xx), the  speed commanded by the autothrottle will not degrade to a speed lower than that inputted.

The default display is +5 knots.   Changing this figure will alter how the algorithm calculates the command speed for the autothrottle; any change will be reflected in the LEGS page, however not in the APPROACH REF page.

The data entered into the Wind Correction field will only be used by the Flight Management System (FMS) when the aircraft is following an RNAV approach, or when using VNAV to fly an approach that has been manually constructed in the CDU.  This is because these approach modes use the data from the FMS to fly the approach (as opposed to an ILS or other mode that doesn't use the FMS data). 

If hand flying the aircraft, or executing another approach type, Wind Correction is advisory (you will need to add the speed additive (Vref+ xx knots) by mental mathematics).

Important Points:

  • Wind Correction is automatically added to Vref when flying an RNAV approach, or when using VNAV to fly an approach that has been manually constructed in the CDU.

  • Wind Correction is advisory for all other approach types or when manually flying an approach; +xx knots must be added to Vref by mental mathematics.

How To Use WIND CORR

The WIND CORR feature is straightforward to use.   

Virtual CDU (ProSim737) showing the difference in landing speed with a Vref between a +5 and +13 Knot (Wind Correction) change.  Vref altered from 152 knots to 160 knots

Navigate to the approach page in the CDU (press INIT REF key to open the Approach Reference page).  Then double press the key adjacent to the required flaps for approach (for example, flaps 30).  Double selecting the key causes the flap/speed setting to be automatically populated to the FLAP/SPD line. 

Type the desired additive into the scratch pad of the CDU and up-select to the WIND CORR line.  The revised speed will change the original Vref speed and take the headwind component into account.  If you navigate to the LEGS page in the CDU, you will observe the change.

If the headwind is greater than 5 knots, then WIND CORR can be used to increase the additive from the default +5 knots to anything up to but not exceeding 20 knots. 

It’s important to understand that the figure generated in the CDU is the Vref speed.  This is the speed that the aircraft should be at when crossing the runway threshold or at a altitude of approximately 50 feet.  

To this speed you must add the appropriate wind correction - either by mental mathematics or by using WIND CORR (if flying an FMS generated approach).

Boeing state that the +XX knots should be bled off during the flare procedure ensuring that touchdown speed is at Vref, however this rarely occurs in real life.

Recall from above, that any change using the Wind Correction field will have no bearing on calculations, unless the aircraft is being flown in RNAV / VNAV, or the approach has been manually constructed in the CDU.

For a full review on how to calculate wind speed, refer to this article: Crosswind landing Techniques - Calculations. A prompt sheet is displayed for quick reference.         

Wind calculation cheat sheet

Important Variables - Aircraft Weight and Fuel Burn

To obtain the most accurate Vref for landing, the weight of the aircraft must be known minus the fuel that has been consumed during the flight.

Fortunately, the Flight Management System updates this information in real-time and provides access to the information in the CDU.  It's important that if an approach is lengthy (time consuming) and/or involves holds, the Vref data displayed on the CDU will not be up-to-date (assuming you calculated this at time of descent); the FLAPS/Vref display will show a different speed to that displayed in the FLAP/SPD display.  To update this data, double press the key adjacent to the flaps/speed required and the information will update to the new speed.

How To Manually Calculate Fuel Burn

If wishing to manually calculate the final approach speed well before the approach commences, then it's necessary to manually calculate the fuel burn of the aircraft.  Open the PROGRESS PAGE on the CDU and take note of the arrival fuel.  Subtract this value from how much fuel you have in the tanks - this is the fuel burn (assuming all variables are constant).

Interestingly, the difference that fuel burn and aircraft weight can play in the final Vref speed can be substantial (assuming all variables, except fuel, are equal).  To demonstrate:

  • Aircraft weight at 74.5 tonnes with fuel tanks 100% full – flaps/Vref 30/158.

  • Aircraft weight at 60.0 tonnes with fuel tanks 25% full   – flaps/Vref 30/142.

Important Points:

  • During the approach, V speeds are important to maintain.  A commanded speed that is below optimal can be dangerous, especially if the crew needs to conduct a go-around, or if winds suddenly increase or decrease.  An increase or decrease in wind may cause pitch coupling.

  • If executing an RNAV Approach or using VNAV, it's important to update the WIND CORR field to the correct headwind speed based on wind conditions.  This is because an RNAV approach and VNAV use the data from the Flight Management System (to which Wind Correction is added).

  • If an approach is lengthy (for example, during a STAR or when requested to hold), the Vref speed will need to be updated to take into account the fuel that has been used by the aircraft during the holding time. 

  • Changing the WIND CORR speed in the CDU, does not alter the Vref speed displayed on the Primary Flight Display (PFD).  Nor is the APPROACH REF page on the CDU updated.  The change is only reflected in the LEGS page.

  • Boeing state that the speed additive should be 'bled off' during the flare so that the actual landing speed is Vref.

Autoland

Autolands are rarely done in the Boeing 737, however, if executing an autoland, the WIND CORR field is left as +5 knots (default).  The autoland and autothrottle logic will command the correct approach and landing speed.

Simulated in Avionics Suite

WIND CORR may or may not be functional in the avionics software you use.  Wind Correction is functional in the ProSim737 avionics suite.

Additonal Information

A very good video that discusses this in detail can be viewed at FlightDeck2Sim.

 
 

Acronyms

  • CDU – Control Display Unit

  • FMC – Flight Management Computer

  • FMS – Flight Management System (comprising the FMC and CDU)

  • Vref - The final approach speed is based on the reference landing speed

  • Vapp – Vapp is your approach speed, and is adjusted for any wind component you might have. You drop from Vapp to Vref usually by just going idle at a certain point in the flare

  • Updated 21 March 2022 (increased clarity)

Differences in Colour, Manufacturer, and Layout in the Center Pedestal

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There are several panels that make up the center pedestal, main instrument panel, and overhead in the Boeing 737 aircraft. Most of the panels are required by international law, and a carrier cannot fly if certain panels do not function correctly.

Although the aviation regulations require aircraft to have certain panels, there are panels that are airline specific. These panels are chosen when the aircraft is ordered from Boeing, or they may be installed at a later on. Similar to automobiles, there are a number of manufacturers of aviation panels and each panel, although having identical functionality may differ slightly.

All high-end simulators replicate the panels required by the authorities, and enthusiasts often fixate on a number of supposed issues. Namely:

(i)         The colour of the panel and lightplate;

(ii)        The position of the panel in the center pedestal;

(iii)       The backlighting of the lightplate (bulbs verses LEDs);

(iv)       The manufacturer of the panel, and;

(v)        The aesthetic condition of the lightplate.

Although seemingly important to a cockpit builder, to the casual observer, or indeed to many pilots, these attributes are of little consequence.  Nevertheless, it's understandable to a newcomer that all panels in the 737 Next Generation are identical between all aircraft.

Whilst it's true that all airlines must meet aviation standards for the type of operation they fly, the panel manufacturer and where in the pedestal the panel is located is at the discretion of the airline.  Furthermore, it's not uncommon to observe older style panels mixed with modern panels and to see lightplates that are illuminated by bulbs and LEDs side by side.

Note that some of this information probably pertains more to older Next Generation 737s than to the latest Next Generation released from Boeing.  I use the word 'panel' to denote an avionics module.

Air Alaska 737-700 pedestal.  Note higher than standard position of ACP panels and relocated position of the door lock panel.  Also high mounted position of rudder trim panel

Colour of Lightplates

The official colour shade used by Boeing is Federal Standard 5956 36440 (light gull grey).  However, OEM part manufacturers may use slightly different colour hues.  For example, IPECO use British Standard 381C-632 (dark admiralty grey) and Gables use RAL 7011.  This said, often an airline will 'touch up' a lightplate that is damaged or faded - this introduces a further colour variant. 

For example, a lightplate I acquired from a 737-500 airframe revealed three differing shades of grey beneath the final top coat of paint.  This is not to mention that, depending on the manufacturer of the lightplate, the final coat of paint may be matt, semi-matt or gloss.

From the perspective of an engineer, the colour (and to a certain extent aesthetic condition) is unimportant when replacing a defective part with another.  Time spent in the hanger equates to a loss in revenue by the airline.  Therefore turn-around times are as brief as possible and keeping an aircraft on the ground while procuring the correct shade of Boeing grey does not enter the equation.

Position of Panels in the Center Pedestal

Boeing recommends a more or less standard position for the essential panels in the center pedestal (NAV, COM, ADF, ASP, rudder trim, door lock and panel flood), however, the location of the panels is often altered by the receiving airline, and is to a certain extent is determined by what other panels are installed to the pedestal.  Areas (holes) in the pedestal not used by a panel are covered over with a grey-coloured metal blank.

LEFT:  This photograph of the center pedestal of a Boeing 737-500 was taken in 2016.  The aircraft is a freighter converted from a passenger aircraft.  Apart from the older style ACP panels, note the disparate displays between the NAV and COM radios.  Also note the position of the ADF radios and some of the other panels; they do not conform to what is usually thought of as a standard set-out.  Finally, note the scratches on the pedestal and on some of the panels and lightplates - they hardly look new.

Panels are manufactured by several companies, and often there appearance will differ slightly between manufacturer, although the panel's functionality will be identical.  The airline more often than not chooses which panel is used, and often the decision is biased by the cost of the panel.  Therefore, it's not uncommon to observe several airframes of a similar age with differing panels positioned in different areas of the center pedestal.

Panel Condition

Enthusiasts pride themselves in having a simulator that looks brand new.  However, in the real world a Level D simulator or flight deck rarely looks new after entering service.  Panels can be soiled and paint is chipped and scratched, and depending on age, some lightplates are faded to due to the high UV environment that is present in a flight deck.

So where am I going with this?  Enthusiasts strive to match their panels with those observed in a real airliner, however, more often than not this information comes from photographs distributed by Boeing Corporation, which nearly always depict panels in a standard position, especially in relation to the center pedestal. 

The variables noted by enthusiasts should not cause consternation, as real aircraft show similar variation.  Remember that in the real aircraft, colour, manufacturer, and to a certain extent aesthetic condition is not important - functionality is.

Backlighting and Dimming with OEM and Reproduction Panels

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FDS-IBL-DIST-DIM.  A card that makes diming backlighting very easy.  Potentiometer is not shown

Many enthusiasts are now using Original Aircraft Equipment (OEM) panels in their simulators.  These panels are connected to Flight Simulator using a variety of interface cards.  Unless the flight deck uses all OEM panels, or all reproduction panels, there will be a difference in backlighting when the light plates are illuminated.

Reproduction panels, with the exception of expensive very high end types, will have exceptionally bright backlighting.  Manufacturers of reproduction panels want their panel to look good and appeal to a prospective buyer – this is why they have bright backlighting.  In contrast, OEM panels do not have  bright backlighting, and in some cases, depending upon the manufacturer of the panel, the backlighting will appear rather dim.  

Therefore, the brightness of the backlighting when using ‘run of the mill’ reproduction panels is not realistic in comparison to that observed in a real aircraft.

So how does a cockpit builder solve this conundrum of brightness if he or she has a mix of reproduction and OEM panels.  The solution is very simple – install a dimmer switch into your flight deck.

Dimmer Control

There are a number of 5 volt dimmer switches on the market and some are better than others.  For those with electrical knowledge it’s relatively straightforward to make your own dimmer switch, but what about the rest of us?  An excellent solution is the distribution board with built in dimmer control manufactured by Flight Deck Solutions (FDS).  The board keeps with the principle of KIS (keep it simple).  

FDS-IBL-DIST-DIM

The distribution board is well made, small, is fuse protected, and have the capability to connect up to 14 accessory LEDS or bulbs via propriety board connectors.  The board also can be used as a slave, meaning it can be daisy-chained to another board to increase the number items attached.

The distribution board includes a pre-wired metal potentiometer which allows all the LEDS/bulbs attached to the board to be dimmed from on to off or anywhere in-between.  The potentiometer is a standard size and fits the hole located in the panel lights panel on either a reproduction panel or an OEM panel.

One limiting feature that should be noted is that each distribution board will only support 10 amps - the rating of the fuse.  Therefore, depending upon the number of panels that you wish to connect to the board, it may be necessary to use two boards in parallel rather one board or an extension to the board.

Of more importance, the board operates flawlessly and is a very easy solution to maintaining an even brightness across reproduction and OEM panels; adjust the brightness of the reproduction panels to the same level as the OEM panels.

Connection

Connection is straightforward and requires +- 5 volts to be connected to the board.  Each LED (or bulb) that requires dim control is then connected to the board connectors.  If using an FDS panel this is very easy as the FDS panels already use the correct female attachment plugs (FDS also use bulbs and not LEDS).  Failing this, a little extra work is required to source the correct plugs and wire them to the +- wires that connect to the light plate.

Bulbs and LEDS

On another note, with the exception of late model airframes, the Next Generation B737 use 5 volt incandescent bulbs in their panels for backlighting.  This is in contrast to reproduction panels that, for the most part, use LEDS.  

The difference between bulbs and LEDS, other than construction, is the temperature they generate when turned on.  A bulb will generate considerable heat and the colour of the light will appear as a warmer hue.  A LED does not generate heat when turned on.  Therefore, an LED will have a cooler temperature and the colour of the light will be colder and more stark in its appearance.

However, before changing out all your bulbs or LEDS to maintain colour consistency, study the flight deck of a real aircraft.  Panels on all aircraft fail or need upgrading from time to time.  Therefore, it is not unrealistic to have a flight deck consisting of both LEDS and bulbs.  Airlines are in the business of making money, and pilots fly.  Neither are particularly interested in whether the ADF radio has a bulb or LED.

Additional Information

Soar-By-Wire has also discussed this subject.  Although his information relates to the Airbus, the same procedure can be done for Boeing OEM panels.

Disclaimer

I do not represent Flight Deck Solutions or any other manufacturer and have no received any fee or reward for discussing one of their interface components.

Further information pertaining to the distribution board can be found on the Flight Deck Solutions website.

A fellow enthusiast has written more information on his website about the distribution board as it relates to Airbus - Soarbywire.  What he has written is well worth the time reading.

Sounds Reworked - Flight Sim Set Volume (FSSV) - Review

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Engine sounds will be at their highest at takeoff

Immersion is a perception of being physically present in a non-physical world.  The perception is created by surrounding the user of the simulator in images, sound or other stimuli that provide an engrossing total environment.  When something does not replicate its real world counterpart, the illusion and immersion effect is degraded.

Engine Sound Output

The sound output generated by a jet aircraft as heard from the flight deck is markedly different when the aircraft is at altitude.  This is because of differences in air density, temperature, the speed of the aircraft, drag, and thrust settings.  The noise emitted from the engines will always be highest at takeoff when full thrust is applied.  At this time, the noise generated from wind blowing over the airframe will be at its lowest.  At some stage, these variables will change and wind noise will dominate over engine noise.

As an aircraft gathers speed and increases altitude, engine sound levels lower and wind levels, caused by drag, increase.  Furthermore, certain sounds are barely audible from the flight deck on the ground let alone in the air; sounds such the movement of flaps and the extension of flight spoilers (speedbrake).

Being a virtual flyer, the sound levels heard and the ratio between wind and engine sound at altitude is subjective, however, a visit to a flight deck on a real jet liner will enlighten you to the fact that that Flight Simulator’s constant-level sound output is far from realistic.

Add On Programs

Two programs which strive to counter this shortcoming (using different variables) are Accu-Feel by A2A Simulations and FS Set Volume (FSSV).  This article will discuss the attributes of FSSV (Sounds Reworked).

Flight Sim Set Volume (FSSV)

FSSV is a very basic program that reads customized variables to alter the volume of sound generated from Flight Simulator.  The program is standalone and can be copied into any folder on your computer, however, does require FSUIPC to connect with Flight Simulator.  Wide FS enables FSSV to be installed on a client computer and run across a network.  

The following variables can be customised:

(i)     Maximum volume

(ii)    Minimum volume

(iii)   Upper mach threshold

(iv)   Lower mach threshold

(v)    Engine volume ratio

Each of the variables will alter to varying degrees the Mach, engine %N1, rounded engine speed and volume percentage.  

For the program to have effect it must be opened either prior to or after the flight simulator session is opened. 

FSSV pop-up screen showing customised variables (default) that can be set and current reads-outs for the simulator session

It’s an easy fix to automate the opening of the program to coincide with Flight Simulator opening by including the program .exe in a batch file. 

A pop-up window, which opens automatically when the program is started, will display the variables selected and the outputs of each variables.  If the window is kept open, the variables can be observed ‘on the fly’ as the simulation session progresses.  Once you are pleased with the effects of the various settings, a save menu allows the settings to be saved to an .ini file.  The pop-up window can then be set to be minimized when you start a flight simulator session.  

How FSSV Works

The program reads the sound output from the computers primary sound device and alters the various sound outputs based upon customized variables.  The program then lowers the master volume at the appropriate time to match the variables selected.  FSSV will only alter the sound output on the computer that the program is installed.  Therefore, if FSSV is installed to the same computer as Flight Simulator (server computer) then the sound for that computer will only be affected.

Possible Issue (depends on set-up)

An issue may develop if FSSV is installed on a client computer and run across a network via Wide FS, then the program will not only affect the sound output from the server computer, but it also will affect the sound output from the client computer.  

A workaround to rectify this is to split the sound that comes from the sever computer with a y-adapter and connect it to the line-in of another computer, or use a third computer (if one is spare).

In my opinion, it’s simpler to install and run the program via a batch file on the server computer that flight simulator is installed.  The program is small and any drop in performance or frame rates is insignificant.

Summary

The program, although basic, is very easy to configure and use - a little trial and error should enable the aircraft sounds to play with a higher degree of realism.  However, the level that you alter the variables to is subjective; it depends on your perception to the level of sound heard on a flight deck – each virtual flyer will his or her own perception to what is correct. 

The program functions with FSX and P3D flawlessly. 

Finally, If you are unhappy with the result, it’s only a matter of removing/deleting the folder you installed the program to, or close the program during your simulator session to return the sound levels to what they previously were. 

  • FS Set Volume can be downloaded at no charge here. 

Video

The below video is courtesy of the FSSV website.

 
 
 

Conversion of OEM CDU - Part Two

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OEM CDU operational with ProSim737

In this second article, I will explain how the OEM Control Device Unit (CDU) was converted to enable a SimStack Foundation Board to be installed inside the unit and connected to ProSim737. 

SimStacks are manufactured by Simulator Solutions, which is a Sydney based company in Australia and their foundation boards can be used with ProSim737 and ProSim320 avionics suites. 

This is but one method to convert an OEM item to be used with flight simulator.

This article will mainly address the mechanical conversion of the CDU.  A future article, after flight testing,  will provide a review of SimStacks interface cards.

Conversion

Many of the OEM parts used in the simulator have been converted using Phidget cards, and to a lesser extent Leo Bodnar and PoKeys interface cards.  Phidgets provide a stable platform, despite the disadvantage that they, at time of writing, can only connect via USB to the server computer, and don’t enable every OEM function to be used in ProSim-AR.  The primary advantage of using Phidgets is that they have been used in a wide variety of applications, are inherently stable, and their configuration is well documented.

I decided that, rather than use Phidgets, a different system would be trailed to interface the CDU with ProSim737. 

he SimStack Foundation Board mounted on an angular bracket inside the CDU.  Fortunately there is ample room to mount the board inside the CDU

SimStacks by Simulator Solutions

The conversion of the CDU was done in collaboration with Sydney-based company Simulator Solutions Pty Ltd.  Simulator Solutions use their propriety interface boards called SimStacks to convert OEM parts for use in commercial-grade simulators.

SimStacks is a modular, stackable, and scalable hardware interface that is designed to integrate OEM parts into your simulator with little or no modification.    One of the many advantages in using a SimStack board is that the interface can connect with either the server or client computer via Ethernet (as opposed to Phidgets). 

To date, Simulator Solution’s experience has been predominately with the conversion of B747 parts and Rodney and John (owners) were excited to have the opportunity to evaluate their software on the 737 platform using ProSim737. 

Converting the CDU - Choose Your Poison

There are two main camps when discussing how to convert an OEM part.  The first is to use as much of the original wiring and parts as possible.  The second is to completely ‘gut’ the part and convert it cleanly using an interface that connects seamlessly with the avionics software in use (ProSim-AR).  A third option, although expensive and in many respects ‘experimental’, is to use ARINC 429. 

ARINC 429 is a protocol used in real aircraft to enable panels etc to be connected with the aircraft’s systems, and although it can be used in a simulated environment, it’s not without its shortfalls, in particular, the use of AC power (in contrast to DC power).

To use SimStacks the internal components of the CDU had to be removed, with the  exception of the internal shelf divider and keypad.  In hindsight, the pin-outs of the Canon plugs could have been used, but in doing so a female Canon plug would have been required, and for the use of a couple of pins, the price of a Canon female plug was expensive.

Keypad and Screen

The keypad and screen are the two most important parts of the CDU. 

The keypad forms part of the lightplate.  The backlighting for the keypad is powered by 21 5 Volt incandescent bulbs, strategically located to ensure even backlighting of the keys.

table 1: provides an overview of bulb location, part number and quantity

Like anything, bulbs have a limited left and, although OEM bulbs are renown for their longevity, there is always a chance that some bulbs are broken.  In this case, there were 3 bulbs that needed replacement.

Disassembling and removing the keypad from the main body of the CDU is straightforward; several small Philips head screws hold the keypad in place.  Once the keypad has been removed, any ‘blown’ bulbs can be replaced. 

The most important area is the keypad is what is called the terminus (bus).  Several wires from the keypad travel to the bus and then to the various (now removed) parts in the CDU.  The Simstack Foundation Board is wired to the bus, therefore, care must be taken to not damage these wires between the bus and the keypad. 

737 CL CDU showing older green coloured text displayed on CRT screen

I found that the wires were quite short and needed to be lengthened; this can be done by splicing longer wire to the existing wire.  Although it's possible to replace the wire to the keypad, this would entail re soldering the wires to the various keypad points - a process that requires very exact soldering.

CRT screen showing thick curved glass

CRT and LCD Screen

The Classic CDU from airframes up to the Boeing 737-500 is fitted with a solid glass cathode ray tube (CRT) screen. 

The CRT screen is approximately 2 cm thick, curved in design, and fits snugly within the display frame of the CDU.  Although it’s possible to make this screen operational, the display will be mono-colour (green) and the screen resolution poor.  Therefore, the CRT was replaced with a custom-sized high resolution colour LCD screen.

To replace the CRT screen is not without its challenges.  The first being that the LCD screen is not 2 cm in thickness and will not fit snugly within the curved display recess of the CDU frame.  To rectify this shortfall, a piece of clear glass must be ground to correctly fit within the frame.  This piece of glass replaces the 2 cm thick, curved CRT glass.

Photo showing how the thin LCD screen was secured with tape the glass screen.  Although the process appears rudimentary, it's functional

The thin LCD screen is installed directly behind the clear glass using high density tape.  Commercial grade double-sided sticky tape is the easiest method, but it is rudimentary.  The reason that tape is used, is that should the screen fail, it’s easy to remove the tape, install a replacement screen, and then tape the screen in place.

During the design phase, it was thought that the thick piece of glass would cause a refraction problem.  However, although the theory suggests refraction will occur, the practical application has been such that any refraction is not readily noticeable.

Installing the SimStacks Foundation Board and Screen Controller Card

To enable the CDU to operate, four items need to be mounted inside the CDU.

(i)   The generic Interface card that controls the LCD screen;

(ii)   The LCD screen controller (buttons that control brightness, contrast, etc);

(iii)  The SimStack Foundation Board; and,

(iv)  The wiring to connect the keyboard to the Foundation Board.

Fortunately, there is ample room in the cavernous interior of the CDU to fit these items. 

The SimStack Foundation Board is mounted on an angular metal bracket that is attached directly to the bottom of the CDU, while the LCD interface card has been installed on the upper shelf along with the screen controller.  A ribbon cable connects the LCD screen to the interface card while a standard VGA cable connects the LCD screen to the client computer and Ethernet switch. 

The SimStack Foundation Board is Ethernet ready and requires a standard Ethernet cable (CAT 6) to connect from the card to an Ethernet switch (located behind the MIP).  In addition to the Ethernet  and VGA cable, six power wires leave the CDU via the rear of the casing; four from the SimStack Foundation Board (5 and 12 volts +-) and two from the keypad (5 volts +-) to control the backlighting.

The specialist switch and wiring (Ethernet, power and VGA cables) extruding from the rear of the CDU

Specialist Switch and Power Supply

A standard two-way toggle switch is mounted to the rear of the CDU casing. 

This switch is used to control whether the LCD screen, used in the CDU, is always on, or is only turned on when ProSim-AR is activated.

To operate the CDU requires a 5 and 12 volt power supply.  The backlighting of the keypad is powered by 5 volts while the SimStack Foundation Board and CDU operation require 12 volts.

Backlight Dimming (keypad)

To enable the CDU keypad to be dimmed, the 5 volt wires are connected to a dedicated 5 volt Busbar located in the center pedestal.  This Busbar is used to connect the backlighting from all OEM panels.  The Busbar is then connected to the panel knob on the center pedestal.  The ability to turn the backlighting on and off is controlled by opening or closing a 12 volt relay (attached in line between the panel knob and Busbar).  Dimming is controlled by a dimmer circuit (see earlier article).

Installing the OEM CDU to Flight Deck Solutions MIP

It can be challenging attempting to install OEM panels, gauges and other items to a reproduction Main Instrument Panel (MIP).  Unfortunately, no matter what the manufacturer states, many MIPS do not comply with real world measurements.  

Before and after photograph of the FDS CDU bay showing the small flange from the shelf that needed to be trimmed to enable the CDU to slide into the bay recess.  A small notch was made at the corner to facilitate the safe routing of the wires used to enable the Lights Test

The MIP skeleton is manufactured by Flight Deck Solutions (FDS) and the CDU bay, although fitted with OEM DZUS rails, is designed to fit FDS’s propriety CDU unit (MX Pro) and not an OEM unit. 

The casing for the OEM CDU is much longer than the FDS CDU and measures 20 cm in length.

The FDS MIP design is such that the aluminum shelf (used by FDS to mount various interface cards) protrudes slightly into the rear of the CDU bay.  This protrusion stops the OEM casing from sliding neatly into the bay to its fullest extent.  To enable the CDU to slide into the CDU bay, the shelf must be ‘trimmed’.

To trim the metal away from the shelf, a small metal saw was used, and although an easy task, care must be taken not to ‘saw away’ too much metal.  Once the piece of offending aluminum is removed, the CDU slides perfectly into the bay, to be secured by DZUS fasteners to the DZUS rail.

Functionality and Operation

The CDU is not intelligent; it’s basically a glorified keyboard that must be interfaced with ProSim-AR to enable the CDU to function correctly.  The fonts and colour of the fonts is generated by the avionics suite (in this case ProSim-AR, but arguably it could also be Sim Avionics or Project Magenta). 

To enable communication between the avionics suite and the SimStack Foundation Board, proprietary software must be installed.  This software has been developed by Simulator Solutions.

SimStack Software (simswitch)

Screen grab showing SimSwitch software User Interface.  SimSwitch is standalone once the initial configuration has been completed.  The software can be configured to open in minimised mode via a batch file

To enable communication between the Foundation Board and ProSim737, propriety software, called SimSwitch must be installed to the computer that has the CDU connected. 

SimSwitch is a JAR executable file, that when configured with the correct static IP address and port numbers, provides communication between ProSim-AR (on the server computer) and the network (clients).  The switch must be opened for communication to occur between the Foundation Board, SimSwitch and ProSim737.  The jar file can easily be included into a batch file (with timer command) for automatic loading when flight simulator is used.

When opened, SimSwitch displays the User Interface.  The User Interface displays all OEM panels that have been connected using a SimStacks, can be used to monitor connected panels, and can display debugging information (if required).

Independent Operation

The Captain and First Officer CDUs are not cloned (although this is easy to do), but operate as separate units.  This is identical to the operation in the real aircraft, whereby the Captain and First Officer are responsible for specific tasks when inputting the information into the CDU.

First Officer CDU

The First Officer CDU will be converted using a similar technique, with the exception that this unit will be converted more ‘cleanly’.  Rather than use an angled plate on which to attach the SimStacks Foundation Board, a solid aluminum plate will be used.  The LCD screen controller card will also be attached to the rear of the LCD screen.  Finally, to enable fast and easy removal of the CDU, the connection of the Ethernet cable will be outside of the unit.

Additional Information

SoarByWire (another enthusiast) has written an excellent article dealing with interfacing SimStacks.

Below is a short video demonstrating the operation of the OEM CDU using ProSim737.

Main points to note in the video are:

  • Heavy duty tactile keys.

  • The definite click that is heard when depressing a key.

  • The solid keypad (the keys do not wobble about in their sockets).

  • Although subjective, the appearance of the OEM CDU looks more aesthetically pleasing that a reproduction unit.

 
 

Final Call

The conversion has been successful and, when connected with ProSim737 via SimSwitch, all the functions available in the CDU work correctly.

Glossary

  • ARINC 429 –  A standard used to  address data communications between avionics components.  The most widely used  standard is an avionics data bus.  ARINC 429 enables a single transmitter to communicate data to up to 20 receivers over a single bus.

  • Standalone – Two meanings.  Operation does not require an interface card to be mounted outside of the panel/part; and, In relation to software, the executable file (.exe) does not need to be installed to C Drive, but can be executed from any folder or the desktop.

  • Updated for clarity and information 12 June 2020.

MCP and EFIS By SimWorld - Review

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Mode Control Panel (MCP) by SimWorld.  The image looks impressive and the looks do not deceive as this MCP has many advantages over other panels. (promotional photograph © SimWorld

This article will review and evaluate the Mode Control Panel (MCP) and Electronic Flight Instrument System (EFIS) produced by SimWorld in Poland.  It will also briefly examine the use of the CANBUS controller system (SimBox). 

The MCP will be discussed first followed by the EFIS and CANBUS system.  Where some areas overlap they will be discussed together.  I use the word panel to denote either the MCP or EFIS.  Also, OEM is an acronym for Original Equipment Manufacturer (aka real aircraft part).  

This review is not endorsed by SimWorld and is entirely my view based on first-hand experience using the MCP and EFIS.  

Background

The mainstay for several years has been the MCP and EFIS produced by CP Flight in Italy.  For the most part, these panels have delivered consistent and reliable performance, despite their rather dated design and engineering.  

However, there are several distinct differences in aesthetics and functionality between the CP Flight units and OEM counterparts.  Furthermore, many CP Flight panels had connection problems caused by the nature of how the MCP was connected to the server computer (using a virtual communication port).  

Reason for Updating MCP and EFIS

Until updating to the SimWorld MCP and EFIS, I had used the panels manufactured by CP Flight (2015 Pro USB interface model), but technology is not idle.  The use of high-end CNC machines and electronics has enabled many parts to me made, that are in many respects indiscernible from the real item.

Initially, I attempted to find OEM panels.  Although the older non-Collins style MCP could be found, it wasn’t possible to find the newer Collins unit at an affordable price.   

SimWorld provides, at the time of writing, the closest resemblance to the OEM panels.  Furthermore, the use of the CANBUS enables trouble-free connection.

Pre-Sale

The MCP and EFIS are not inexpensive; add to this Government import charges and UPS freight and you have spent a considerable sum of money.   With an increased price comes the expectation of higher quality, reliability, robustness, and attention to detail; let’s examine how SimWorld shapes up to this maxim.

The SimWorld website provides considerable information, including photographs and a video demonstrating the MCP and EFIS.  Although imagery can save a thousand words, questions usually need to be asked.   Filip and Piotr spent considerable time answering my specific queries and e-mails were replied to in a timely manner.   Their customer focus has been top shelf in every respect.

Aesthetics, Manufacture and Detail - MCP

The Mode Control Panel (MCP) and Electronic Flight Instrument System (EFIS) are the main avionics panels used in a simulator, and most enthusiasts strive to replicate the appearance and functionality of these panels as closely as possible to the those in the real aircraft.  

Quick List – Main Advantages (SimWorld MCP):

(i)         1:1 in comparison to the OEM MCP;

(ii)         Correct Boeing-grey colour;

(iii)        Screws located in the correct location on the front panel;

(iv)        Flight Director thumb stops;

(v)         Use of externally protected printed circuit boards (PCBs);

(vi)        Motorised autothrottle arming switch with automatic release to off;

(vii)       Ambient sensor (2017 MCP model, not functional);

(viii)      Does not use seven-segmented displays;

(ix)       Ability to accurately display +- and other specialist fonts;

(x)        Push to engage annunciators are backlit in green (when depressed) and are separate to the colour of the backlighting;

(xi)       Integrated backlighting uses a built-in PCB for reliable dimming control;

(xii)      Correct styled knobs made from painted aluminum;

(xiii)     Correct smoky-coloured display windows positioned in frames identical to the OEM MCP;

(xiv)     Functionality that replicates the OEM MCP (depends on avionics suite used); and,

(xv)      Use of commercial grade rotary encoders.

External casing removed showing multiple Printed Circuit Boards

Internal Components

The components for the MCP and EFIS panels are for the most part machine-made; however, the components are assembled by hand on a market-demand basis.   To ensure production repeatability, SimWorld use a number of printed circuit boards (PCBs) sandwiched together to provide core functionality.

A PCB contains numerous ‘tracks and pads’, that are used for input and output devices, memory chips and processors, and various electrical components such as resistors and capacitors.  An advantage of using PCBs is that troubleshooting can be done via a tethered computer, and if a problem is detected, a board can easily be replaced.  This is because, theoretically, each PCB for each panel is identical in design, layout and population.

System Logic and Functionality

The MCP and EFIS are a hardware-user interface that has been designed from the outset to provide full flexibility in relation to functionality.   However, although the panels may have the appropriate hardware in place, the logic to enable the functionality to operate is supplied by the avionics suite in use (for example, ProSim-AR).  

MCP Light Plate

The light plate has been professionally made and the various pre-cut holes (cut-outs) are well finished.  The laser-engraved lettering on the light plate is precise, evenly cut, and does not differ across the unit.  Additionally, the colour of the paint is the correct Boeing gray and does not differ in hue between the MCP and EFIS light plates.

The manufacture of a light plate is quite involved, and an individual plate or batch will take on average 3 days to complete.   Prior to cutting, several thin layers of paint are applied to the light plate.  A laser is then used to engrave the required letters down to the white-coloured base layer.  The base layer is transparent to light, and when backlit, the lettering can easily be read.

SimWorld use the same technology (or very close to it), that is used to manufacture the OEM light plate.

Exterior Casing

The light plate is attached to a series of printed circuit boards (PCBs).  The PCBs and electronics are protected by a 1 mm thick exterior casing.  The casing is made from aluminum and measures 3 inches in depth perpendicular to the front of the light plate.  The casing is powder coated and coloured black.

On the rear of the panel is a female 12 Volt DC power connector, and a connection for the plug that connects the MCP to the CANBUS system.

Detail of heading knob and bank selector pointer.  Note the detail in the window bezel and the well defined laser engraving on the lightplate

Knobs

The appearance and colour of the knobs is very similar to the OEM knobs.  Each knob, with the exception of the vertical speed wheel, is made from machine-cut aluminum and is the correct colour.  The knobs are well finished with no sharp edges, or left over metal from the milling process.   One or two metal set screws secure each knob to the shaft of the rotary encoder.

The heading knob incorporates a functional bank selector pointer (made from plastic), and the vertical speed wheel is produced from high grade molded plastic.  There are no injection holes in the plastic and the end finish passes scrutiny.

The knobs are tactile (feel solid to touch) and when rotated generate a well-defined audible click (similar to the OEM knobs on the MCP).  

Rotary Encoders

Not all rotary encoders are made equal: a high-end encoder is constructed to an exacting standard predominately using metallic components.  To rotate such an encoder requires a mild effort; there is resistance – it isn’t difficult, but you can’t move it left or right with a flip of a finger.   

In comparison, hobbyist-style encoders are considerably cheaper to purchase, are made to a less exacting standard and usually have a shaft and body produced from plastic.  The encoders are easy to rotate and can also wear out prematurely with extended use.

SimWorld use quality Swiss made rotary encoders, rather than using low quality encoders from China.  Each encoder has a cylindrical metal shaft.  A metal shaft is important as a plastic shaft can wear prematurely, in addition to becoming damaged from overzealous tightening of set screws (which hold the knob in place).

I have been told that military specification (MilSpec) encoders are available, however, SimWorld use these encoders only for high-end commercial simulators.

Resistance When Rotating Knobs - Comparison With OEM Honeywell and Collins MCP

Resistance when rotating the knobs will depend on the MCP model.  The knobs on the older Honeywell models are very easy to rotate - A finger with just a ‘tad’ of pressure will move the knobs, however, the newer Collins model has more resistance, but the knobs are still very easy to rotate with minimal force.   As one First Officer stated: ‘You can definitely hear a soft click as you move the encoders - especially on the Honeywell models’.

By comparison, the resistance felt when rotating the knobs on the SimWorld MCP, although difficult to quantify, is similar to the resistance felt when rotating the knobs on the OEM MCP – It is realistic and does not feel ‘toy like’.  

The stray light is at the interface where the exterior casing joins the lightplate.  This area is covered by the MIP when the panel is mounted

Backlighting

The backlighting is controlled by a number of 5 Volt light emitting diodes (LEDs).  Each LED has been strategically located in the light plate to ensure even coverage and intensity of light.  

However, the MCP does exhibit slight light bleed along the join between the light plate and the protective casing.  This is not a problem as when the MCP is mounted into the MIP, the stray light is not noticeable.  If necessary, cloth tape can be placed over the join to eliminate any stray light.

Backlight Dimming - Dimmer Interface Card (DIC)

The MCP and Captain-side EFIS can be dimmed together, while The First Officer EFIS is capable of being dimmed independent of the Captain side EFIS.  This is how it occurs in the real aircraft.

To enable the panel backlighting to be dimmed, SimWorld have used a dedicated PCB (DIC).  The use of a PCB ensures that dimming is reliable, accurate, and highly controllable.   The PCB is standalone, is roughly the size of two credit cards and can be mounted anywhere.

The DIC is connected to the CANBUS system via the custom wiring harness and then to the appropriate potentiometer that controls panel backlighting.   Panel backlighting can be dimmed from off to any brightness level.  

To enable dimming, a potentiometer must be wired to the PCB (DIC).  

Power

The MCP requires 12 Volt power, while the backlighting uses 5 Volt power that is connected to the DIC.

MCP Annunciators

The annunciators are not glorified micro-switches, but are push on/off buttons that when depressed emit an audible click.  The resistance felt as the button is pressed, is slightly less than the pressure required to engage an OEM annunciator.  The square push button and frame is made from plastic, and the cylindrical shaft that the button connects with is made from metal.  

SimWorld have replicated each of the square-shaped buttons exceptionally well, and for the most part their external appearance is identical to the OEM counterpart.

Each annunciator is connected to the primary MCP PCB, thus eliminating the use of wires.  If an annunciator is broken during the course of its life, replacement is relatively straightforward and involves soldering the connection of the replacement annunciator to the PCB.

Status Checkerboard and Legend

Each annunciator on the MCP comprises a square push button, a rectangular-shaped checkerboard, and a legend.

The checkerboard is made by engraving a number of holes that, when the annunciator is pressed, enables green-coloured light to be transmitted through the checkerboard.  The checkerboard is similar to the OEM panel and has the same number of engraved holes.

Each annunciator has a legend that uses multi layer technology (proprietary to SimWorld).  Multi layer technology is what enables the backlighting of the checkerboard and legend to be a different colour.  The name of each annunciator (speed, VNAV, N1, etc.) has been engraved into the legend.   

The detail of the annunciators is very good and the jagged appearance of the lettering only becomes apparent when they are backlit.  The backlight intensity is set to 100%

Unfortunately, the engraved letters are not as defined as you would expect; the lettering is slightly jagged in appearance (enlarge above image). 

This is noticeable only when observed very close-up; from a normal distance (seated) this is barely noticeable and therefore, not really an issue.   However, the ability of the legend to transmit light evenly through the cut-out lettering is noticeable as the jagged appearance causes the names to appear slightly ‘furry’ (brighter or dimmer) depending upon the amount of light that can travel through the lettering, and your viewing position.

The annunciator legends and the checkerboard, are illuminated by strategically-placed LEDs.  

Window Bezels and Liquid Crystal Displays (LCDs)

The two main differences that separate an OEM MCP from a reproduction MCP are the design and appearance of the bezels that surround the display window, and how the actual characters (digits) are displayed.

SimWorld have used a black-coloured bezel that surrounds each of the display windows.  The bezel is identical to the bezels in the OEM MCP, and the join between the bezel and the display frame is seamless.

Equally, the use of custom-made Liquid Crystal Displays (LCDs), with each display backlit by one LED, is what causes SimWorld’s design to stand-out above its competition.  

The checkerboard is identical in appearance across all annunciators.  Note the ambient sensor and + character in the vertical speed window.  Also the very slight difference in the illumination of the + sign  Backlightng is set ~50% intensity

The combined use of LCDs and LEDs enables each character (digit) to be displayed in the correct shape, colour and size.  This is in addition to displaying the specific characters used in the speed window (under and overspeed conditions) and the +- symbols displayed in the vertical speed window.

Although appearing rudimentary, this is similar to how the OEM displays are illuminated.  To my knowledge, all other manufacturers of reproduction MCPs use seven-segmented displays.

While the use of this type of display is a positive step forward, it is not without its negatives; if the LEDS are incorrectly positioned, or the throw of light is not even across the rear of the LCD, then the characters will not be evenly lit.  This may cause some of the characters in a display to be brighter or dimmer (hot or cold spot).

To counter against this, quality assurance (QA) must be exceptionally thorough.  I will discuss QA later in this article.

Backlighting at full intensity is excellent

LCD Brightness

As discussed earlier, each LCD is backlit by a single LED (this is how the characters (digits) are illuminated).

The brightness of the digits is linked to the intensity of the backlight dimming.  Therefore, as backlighting is dimmed, the brightness of the LEDs behind each LCD is lowered.   Although this is exactly how dimming operates in the real aircraft, I find that during the day in bright conditions, with the backlighting turned off, it’s difficult to read the digits as their intensity is not very bright.  At night and in low light conditions this is not an issue as the digits can easily be read. 

A solution to this issue is for SimWorld to enable an alternate method (although not as done in the real aircraft) to allow the brightness of the LEDs to be independent of backlighting.

Autothorttle (A/T)

The A/T toggle, controlled by a solenoid-release mechanism, resembles the OEM toggle.

The system logic SimWorld use in the toggle is slightly different to other reproduction MCPs, in that the toggle can only be engaged when certain conditions are met (system logic).

If the correct conditions are not met, then the toggle cannot be engaged; the toggle will not stay in the engaged position (up) but flick back to the disengaged position (down).  Be aware that for this functionality to operate, the avionics suite in use must also have this capability.

Captain-side EFIS panel with backlighting at full intensity.  The lightplate is well made and the laser engraving is well defined enabling even illumination of backlighting accross the panel.  The BARO STD knob has purposely been left slightly left of center.  When the BARO knob is released it will spring back to the central position

Electronic Flight Instrument System (EFIS)

Disregarding OEM panels, the SimWorld EFIS is probably the best on the market (at the time of writing).   Each EFIS replicates its OEM counterpart in both appearance and functionality, and is the correct size (1:1).

Two noticeable positives are the concave-designed push in/out function buttons on the lower portion of the unit, and the use of independent duel rotaries that are centrally spring-loaded.  

Quick List – Main Advantages (SimWorld EFIS):

(i)      Correct size and dimensions (1:1);

(ii)     Use of externally protected printed circuit boards (PCB);

(iii)    Correct Boeing-grey colour;

(iv)    Accurate aluminum knobs with set screws;

(v)     Independent backlighting between Captain-side and F/O side EFIS units;

(vi)    Two speed rotary encoders which auto-center (BARO and MINS);

(vii)   Well defined laser-cut lettering on light plate; and,

(viii)  Concave-designed push buttons.

First Officer side EFIS.  Knob length, functionality and detail are as per the real aircraft as is concave function buttons and well defined lettering and even backlighting across the lightplate

Manufacture and Detail - EFIS

The EFIS has been manufactured and assembled in a similar way to the MCP.  The EFIS panels are 1:1, are the correct shaded grey colour, include the appropriate screws located in the correct location, and have the correct styled knobs.  As with the MCP, the EFIS use printed circuit boards which are then protected by an exterior aluminium casing.

EFIS Light Plate, Backlight Dimming and Exterior Casing

The laser-cut lettering on the light plate is crisp and sharp, and when the EFIS is backlit the light is evenly spread at the same intensity across the panel. 

Both EFIS panels are dimmed through the same dimmer interface card (DIC) used for the MCP, however, the F/O EFIS panel can be dimmed separately to the Captain-side panel (as it is done in the real aircraft).  

The protective casing that each EFIS resides measures 5 inches in depth perpendicular to the light plate.   On the rear of the unit is a female 5-volt DC power connector, and a connection for the plug that connects the EFIS to the CANBUS system.

First Officer side EFIS.  The lettering and black disc is well made.  The metal set screw that attaches the upper knob to the dual rotary can be observed.  The upper knob is self centering

Knobs

The manufacture of the knobs is similar to the knobs used on the MCP, with the exception that a centrally-placed disc has been laser engraved to enable the function name to be backlit.  The lettering on the discs is crisp and sharp.  The knobs are held securely to the rotary shaft by two metal set-screws.  

The pointer (black & white line) on the function selector knob is a transfer that has been glued to the outside of the knob.  The adhesive has been solidly applied and I doubt the transfer will come loose.

Rotary Encoders

The rotary encoders are similar to those used in the MCP and have a metal cylindrical shaft.  Each of the encoders is a double encoder meaning that it has dual functionality.

Specialist Functionality - BARO and MINS

The barometric pressure (BARO) and radio altitude/pressure (minimums) function exactly as those in the real aircraft.  The outer knobs are spring-loaded, and when rotated and released, self-center with the label resetting to the horizontal position.  The knobs also are push to reset.

Each knob has two speeds: a slight turn left or right turn will alter the single digits, while holding the encoder left or right for a longer period of time will change the double digits, and cause the digits to change at a higher rate of speed.   

The below video, taken inside the flight deck of a B73-800 aircraft shows the operation of the OEM BARO and MINS (courtesy Shrike 200).  The SimWorld BARO and MINS knobs operate the same way.

 
 

Concave-shaped Function Buttons

The function buttons on the EFIS are concave in shape and made from plastic (this differs to the rubberized buttons seen on several OEM EFIS panels).  Each button has the name of the function engraved into the button.  The engraved letters are crisp and sharp and when the panel is backlit, the letters are evenly illuminated without hot or cold spots.  

Each button’s mechanism is made from plastic, and while the use of plastic is understandable, metal probably would increase the mechanism’s service life.  

Minor Problem - Sticky EFIS Button

A minor issue developed after installation of the EFIS into the bracket.  Two function buttons when pressed, would not automatically reset themselves (click in and click out).  The problem only presented when the panel was mounted into the bracket faceplate.

After carefully examining the bracket and protective casing, it was found that when the EFIS was mounted into the MIP, the casing was compressed against the button.  This caused the button to remain pushed in.

The problem was resolved by slightly bending the aluminum external casing so that it did not rub against the button’s mechanism. 

Functionality

The functionality of the EFIS is identical to the OEM EFIS.

SimWorld propriety bracket to mount MCP and EFIS into the SimWorld MIP.  The bracket is solid and very well made

MCP and EFIS Bracket

SimWorld provide a sturdy bracket that is used to mount the MCP and EFIS panels to the Main Instrument Panel (MIP).

The bracket consists of a front faceplate and a rigid bracket framework.  Both items are made from 1 mm thick, black-coloured, powder coated aluminum.  The faceplate is precut to allow fitment of the MCP and EFIS.  The framework provides stability to stop the EFIS panels from wobbling in the precut hole.  

Mounting The Bracket To The MIP

The bracket is designed to be used with SimWorld’s propriety MIP, however, the bracket can be used with other MIPs.  Take note that, depending upon which MIP is used, the bracket/MIP may need to be modified.

I retrofitted the bracket to a Flight Deck Solutions (FDS) MIP which was not without its problems. 

Problems Retrofitting The Bracket to the FDS MIP

The FDS MIP, the distance between the Captain-side and F/O-side glarewings did not allow enough room to enable the bracket faceplate to be fitted; the bracket was approximately 1 mm too long, and the bracket framework was too deep to easily slide into the recess of the FDS MIP.

These shortcomings were rectified by shaving away a small portion of the inner side of each glarewing.  This enabled the bracket faceplate to fit snugly between the glarewings.  

To use the bracket framework (which is quite deep), the internal structure of the FDS MIP has to be cutaway, an act that may affect the structure of the MIP.  Therefore, the framework was discarded and only the bracket faceplate was used.  

Without the framework to provide stability, the EFIS panels wobbled somewhat in the bracket faceplate.  To stop the EFIS from wobbling, small wedges made from wood were fabricated and installed between the EFIS and the inside edge of each glarewing.  Once the wedges were installed, the EFIS did not wobble.  The MCP is secured to the bracket faceplate by four screws which inhibits any movement.

A facsimile of the piece of metal that covers the underneath portion of the MCP was made from thin metal, painted black, and the appropriate screws added.

T-taps can damage wires causing connection issues, so should be viewed as a temporary set-up

Wiring Harness

SimWorld supply a high quality wiring lumen that consists of four colour-coded wires with connectors.  The wires connect to the MCP and EFIS, and then to a 5 and 12 Volt power supply, dimming interface card (DIC), and the CANBUS system.  The power connections are standard push pull plugs and the wires that connect the MCP and EFIS with CANBUS use wire tap connectors (T-taps).   The length of supplied wire approximately 12 feet and SimWorld provide a basic wiring diagram.

Wire Connectors

The use of wire tap connectors (wire chomper), although very convenient, should probably be looked at only as an initial connection when testing the panels.  For a more permanent connection, soldering the wires is preferable.  Soldering will remove the possibility of any troublesome connection.  

Let me explain,  the act of pressing the wire into this slotted metal piece bludgeons the wire. The concept behind this is fine – it’s supposed to strip back the insulation on the wire to make contact with the wire itself. The problem is that there is no guarantee that you won’t accidentally catch some of the wire in this process and tear some of the individual wire strands.  Additionally, if the insulation is broken over a wire, there is a possibility of corrosion (oxidation) occurring.  

Power plug and CANBUS connector.  Each panel is connected to CANBUS by one of these connectors, and then to the dimming interface card

Push-Pull Power Plugs

Although the use of a push/pull power plug is standard to many appliances, the connection is not tight.  If pressure is applied to the power cable, it is easy for the plug to become dislodged and loose connection with the MCP or EFIS.  

On a simulator with motion control, vibration could cause the plug to be dislodged.  An easy matter to rectify, the security of this connection should be improved in future designs.

CANBUS Controller System

The CANBUS system (also called Simbox or CAN controller) enables communication between the server computer and the MCP (and specific SimWorld panels) and is a vital part of the SimWorld architecture.

CAN is an acronym for Controller Area Network and is a bus standard designed to allow micro controllers and devices to communicate with each other.  Simply put, CANBUS translates the CANBUS signal, allowing for control and communication through the computer.

The CAN controller system (printed circuit board) resides in a ribbed-aluminum case with two connectors at each end of the case; one side connects with the computer via a standard USB cable while the other side connects, via a specialist connection, to the wiring harness, and then to the MCP and EFIS panels.  The CAN controller does not require a dedicated power supply.

CANBUS module.  Made from aluminium and housing a Printed Circuit Board (PCB), the CAN controller is what connects the MCP and EFIS tot he server computer.  During all trials, CANBUS performed flawlessly with no drop outs, lags or failures

CANBUS is small and light enough that it can be mounted anywhere between the MIP and server computer.  I have the CANBUS unit secured to the rear of the MIP via a Velcro strap.

Connection and Drivers

CANBUS does not require any drivers to operate as it’s detected by ProSim-AR when the software is turned on.  Connection is immediate, and whatever configuration is needed is done automatically through Windows the first time CANBUS in connected to the computer.  

There should not be any connection or communication issues provided you have checked (ticked) the enable SimWorld drivers within the configuration/drivers tab of the ProSim737 software.  

Compatibility

At the time of writing, CANBUS is compatible with ProSim-AR (plug and fly).  A dedicated driver for iFly and PMDG is under development.  Prior to purchase, I would seek the advice of SimWorld to whether CANBUS is compatible with the avionics suite you are using.

Reliability of CANBUS

In one word - 'perfect'.   I have not had the MCP, EFIS or CANBUS disconnect during a flight simulator session.  This is using FSX and ProSim-AR (version 1.49).  As a test, I disconnected the CAN controller during a flight, then reconnected it.  The flight was not disrupted and the re-connection occurred effortlessly.

Robustness and Service Life

The life and serviceability of a product has a direct relationship to how the product is used (or abused) and the duration of use.   Modern electronics are very forgiving, and electronic problems (if any) usually develop soon after an item begins its service life.  If problems are not detected after first use, then it is not unusual for an item to have a considerable service life.

Some of the more common problems that occur with reproduction panels include; failing encoders, damaged plastic encoder shafts, worn out set screws, slippage of knobs, and faulty switches and buttons.  Additionally, knobs may wear out with use, and paint on the lightplate may chip.  

SimWorld have countered potential problems by using printed circuit boards, commercial metal encoders, aluminum knobs, metal set-screws, and by replicated, as much as possible the same processes used in the manufacture of OEM light plates.  

The above said, it's wise to remember that reproduction panels rarely replicate the robustness and exacting standards of an OEM product; therefore, they should be treated with respect and with care.   I expect that in time the paint on knobs will chip and wear thin with use - this is normal wear and tear.  I don't mind this 'wear and tear' look as it is very seldom you a knob that is shiny new - unless the aircraft is new.

Quality Assurance (QA), Customer Service, and My Experience

Put bluntly, when anything is done by hand there must be a very high level of Quality Assurance (QA) to ensure that design specifications and tolerances are met.  QA can be an expensive process as time is needed to inspect each individual panel and then, if imperfections are noted, make required alterations/repairs.

There is a direct relationship between the price that an items costs and the amount and level of QA that is performed.  You would not expect an inexpensive item mass-produced in China to have high QA – and it doesn’t, which is why many Chinese-produced products fail after a short period of time or have obvious defects.   However, if you are purchasing a high-end product with a high price tag then the expectation is that this product will meet specification, will not have problems, and be sold with an excellent warranty and support.

SimWorld realize that enthusiasts demand quality and strive to meet this requirement.  However, not everything passes muster first time around and sometimes products are released that are not quite up-to-standard.   Whenever this occurs the reputation of the company is tested.

To ensure transparency, I have documented the issues below not to provide negative criticism of SimWorld, but to highlight their dedicated customer support and strong company ethics.  

My Experience

The first MCP and EFIS sent to me from SimWorld did not meet my expectations and had several issues.  Namely:  

(i)     Uneven brightness of the characters (digits) across the five LCDs with some characters presenting as hot spots;

(ii)     Rotary encoders cross-referencing values;

(iii)    A/T arming toggle not locking into the arm position (UP position);

(iv)    Crooked LCD in the course display window; and,

(v)     The light plate on the EFIS was not mounted parallel to the backing plate (crooked).

I contacted SimWorld and they requested that I return the panels to Poland (at their expense) for repair.  

The problems experienced were caused by:

(i)     The positioning of the LED behind the LCD was slightly off center.  This was rectified;

(ii)    The rotary encoders were faulty and had been tracked to a bad batch released from the manufacturer.  They were replaced;  

(iii)   The autothrottle toggle was not aligned correctly with the magnetic plate mounted behind the light plate. This was fixed by moving the toggle very slightly to the left;

(iv)    The crooked LCD was straightened.  As the LCDs are mounted by hand, careful attention must be paid to ensuring they are straight; and,

(v)     The misalignment of the F/O EFIS panel was rectified by making it straight against the backing plate.  

Repaired MCP and EFIS

Unfortunately, following receipt of the repaired MCP, the Captain-side course display would not illuminate.

Piotr at SimWorld organized for my computer to be tethered to their technician’s laptop to enable bench testing.   Unfortunately, the technician could not determine what was causing the problem, but thought it may be a faulty capacitor.  

Rather than attempt to repair the MCP again, Filip arranged for a replacement MCP panel to be sent to me by UPS.  

Replacement MCP Panel

The replacement MCP, by chance, was the newer panel manufactured in 2017.  I have not had any problems with the replacement 2017 model MCP and EFIS.  Both panels function flawlessly and the attention to detail on the panels is beyond reproach.  

Warranty and After-Sales Service

The MCP and EFIS is covered by 12-month unconditional warranty.

The after-sales service and warranty cannot be bettered, and I cannot stress the advantages of dealing with a company that treats its customers with respect and places customer service as a priority.  

In relation to the issues I had with the MCP and EFIS, SimWorld responded to my e-mails within 24 hours, followed up on my questions, provided reasons for the problem, and kept me updated with regard to repairs and/or replacement.   The after-sales service and support provided to me has been exemplary.  

Negatives - MCP and EFIS

It’s difficult to find any major negatives.  However, if pressed they are:

(i)    During the day, the digits displayed in the LCDs are difficult to read if the backlighting is dimmed 100%;

(ii)    The power connection on the rear of the MCP and EFIS is not secure.  If any pressure is applied to a cable, then it’s very easy for the connector to become dislodged from the panel;

(iii)    The laser cutting on the annunciator legends (Speed, V/S, RNAV, etc.) could be more precise (this really is not an issue unless you inspect your panel with a macro lens); and,

(iv)    The non-use of D-shaped shafts on the rotary encoders.  If used, this would minimise the chance of any knob slipping on the shaft of an encoder.

(v)   The brightness of the digits displayed in the LCD's, although more or less even across all characters, does show slight intensity differences.  This is caused by the positioning of the LED that sits behind each LCD. 

Pictures and Videos

I have not included many photographs in an attempt to keep the footprint of the article to a reasonable size. 

I have posted several 'very average' photographs in this gallery in an attempt to show you the appearance of the panels.  Promotional images and videos are fine, but they are always professionally made to show the product in its best light.  You will also see a few images of OEM panels in the gallery to compare.

Below are three professionally made videos courtesy of SimWorld.

The panels displayed in the video accurately reflect the appearance, detail and functionality of the MCP and EFIS.  Equally, CANBUS is as straightforwrd to connect as shown in the video.

 
 
 
 
 
 

Photography

A quick word about photography.  Detailed and close-up photographs will always show unwanted blemishes.  The better the lens the more blemishes will become obvious.  It's important to remember that you do not fly the simulator looking through a magnifying loop, but view panels from a moderate distance.  Even OEM panels show inconsistencies when viewed with a macro lens :)

Titbits

This article has taken several months to complete.  Originally it was three times the length and it's taken some time to condense the information to a length that is readable without it being bound in a book!

Final Call

The price paid to own the SimWorld MCP and EFIS is not inexpensive, however, it is nowhere near the price demanded of a OEM Collins panel, or a panel used in a commercial simulator trainer.

SimWorld's use of liquid crystal displays in lieu of seven-segmented displays, the resistance felt when turning the various knobs that closely match the OEM panels, and the close attention paid to detail: for example, the small tabs beside the Flight Director switches, detailed display bezels, ambient sensor, and realistic push to reset barometer and minimums knobs, is what separates this MCP and EFIS from its competition. 

If you want the appearance of the MCP and EFIS to be as close as possible to the OEM equivalent, and want accurate functionality, then you should not discount the panels produced by SimWorld.

Altitude and Speed Intervention Explained

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Altitude Intervention (ALT INTV) button

The flight deck can be an extreme work environment, especially during the high-task descent and approach phase of the flight. 

Altitude and Speed Intervention were designed to allow pilots to easily and quickly change either the altitude or speed of their aircraft without re-programming the FMC, disengaging VNAV, or spending excessive time 'heads down'.

The intervention buttons are strategically located on the MCP.  When the buttons are selected, the aircraft's altitude or speed can be altered quickly on ‘the fly’. 

In this article, I will examine the use of Altitude and Speed Intervention and demonstrate the use of these modes.  In a follow-on article, I will discuss alternate methods that can be used to change altitude whilst maintaining Vertical Navigation.  The reason for separating the two articles, is to avoid confusion that can develop between the different modes.

In this article I use the words Cruise Altitude (CRZ ALT) and Flight Level (FL) interchangeably.  Also to avoid confusion the Control Display Unit (CDU) is the keypad used to interface with the Flight Mode Computer (FMC) that forms part of the Flight Management System (FMS).

I recommend reading the appropriate section in the Flight Crew Operations Manual (FCOM), Flight Crew Training Manual (FCTM) and the Cockpit Companion for a more thorough understanding. 

Furthermore, whether intervention modes function in the simulator will depend upon which avionics suite and FMC software version is used.  This article will deal only with ProSim-AR (ProSim737 avionics suite) which at the time of writing uses U10.8 A. 

Important Points:

  • Altitude and Speed Intervention are company options that may or may not be ordered at the time of airframe purchase.

  • Altitude and Speed Intervention will only operate when a route has been programmed in the CDU, and is active.  VNAV must be selected for either intervention mode to function.

  • Altitude and Speed Intervention is more often used when a temporary change in altitude and/or speed is required with a return to the original altitude/speed imminent.  

MCP, VNAV & FMA Nomenclature and Displays

Prior to examining Altitude and Speed Intervention, it may be fruitful to quickly discuss common words that are used when describing the operation of VNAV and the MCP.

(i)       CONDITION means that a mode will become active only when a condition(s) occurs;

(ii)      ARM means that a mode is armed pending engagement;

(iii)     ACTIVE means the mode is engaged/selected;

(iv)     SELECT means to select or engage the mode (turn on); and,

(v)      DESELECT means to deselect or disengage (turn off) the mode.

Table 1:  FMA displays observed when Altitude and Speed Intervention is engaged

An often misunderstood facet of the MCP is that the annunciators illuminate to indicate a particular mode is active.  This is not entirely correct, as the presence of an illuminated annunciator (light) does not always indicate whether a mode is active or not.

For example, the VNAV annunciator on the MCP will remain illuminated when VNAV is either active or armed.  Furthermore, active modes that are not able to be deselected, do not display an illuminated annunciator.

To determine whether a mode is active or not, the Flight Mode Annunciator (FMA) should be consulted.  The FMA is located above the Primary Flight Display (PFD) and displays various alerts and status messages.  

Refer to Table 1 (download button at bottom of article) for a synopsis regarding the various displays that the FMA will generate when intervention is used.

Important Points:

  • A mode change highlight symbol (green rectangle) is displayed around the command name, in the Flight Mode Annunciator (FMA), whenever a mode has been armed and is about to become active.  The green rectangle will remain displayed for a period of 10 seconds.

  • It’s prudent to cross reference between the FMA, MCP and CDU to determine what mode is armed or active at a given time.

  • Altitude and Speed Intervention, when active, will take precedence over VNAV, although VNAV will remain armed.

Scenario

The aircraft is flying at FL150 (15,000 feet) at 275 kias.  The FMS has an active route (Company Route) that includes altitude and speed constraints (in the LEGS page of the CDU). 

In level flight, with autopilot, LNAV and VNAV selected, the following will be observed:

(i)     LNAV and VNAV will be active;

(ii)    The FMA will display MCP SPD / LNAV / VNAV PTH or VNAV ALT;  

(iii)   The annunciators on the MCP - LNAV, VNAV & CMD A/B will be illuminated;

(iv)   The speed window located on the MCP will be blank (no speed displayed); and,

(v)    LNAV/VNAV will be displayed in white text on the PFD.

LNAV will be controlling the lateral navigation of the aircraft while VNAV will be controlling the speed and vertical altitude of the aircraft.

ATC request a decrease in speed from 275 kias to 240 kias.

Speed Intervention (SPD INTV) button

Speed Intervention (SPD INTV)

Select (press) the SPD INTV button on the MCP.  The MCP speed window becomes active and displays the current speed of 275 kias.  Dial into the speed window on the MCP the new speed requirement of 240 kias. 

Notice the speed indicator display above the speed tape on the PFD has changed from 275 kias to the new speed of 240 kias.  Also note that the VNAV annunciator light on the MCP remains illuminated - in this case VNAV is active.  The speed of the aircraft will be reduced to 240 kias.

If you cross check with the Cruise Altitude in the CDU (CRZ ALT key/TGT SPD), the CDU will still indicate the original cruise speed of 275 kias.  This is because the speed is an intervention speed and, as such, will not have been updated in the FMC.

If you wish to stay at this speed (240 kias), you will need to manually change the cruise speed to 240 kias in the CDU.  However, in this case the reduction in speed is momentary, and ATC advise you to return to your original speed.  

Returning to Original Speed

Press the SPD INTV button (or unselect and reselect VNAV on the MCP).  Doing this, will return the speed to the original speed (275 kias).  It will also change the speed indication on the PFD from 240 kias back to 275 kias.  The MCP speed window will become blank (no speed displayed) to indicate the VNAV is the controlling mode. 

Important Point:

  • When SPD INTV is active, the FMA will display MCP SPD.  When SPD INTV is not active (deselected) the FMA will revert to FMC SPD.

Altitude Intervention (ALT INTV)

Altitude Intervention is slightly more sophisticated in comparison to Speed Intervention.  This is because, amongst other factors, the relationship changes dependent on whether the aircraft is ascending or descending, and whether there are active restrictions (constraints) programmed for waypoints (U10.8.A).

In level flight, with autopilot, LNAV and VNAV engaged, the following will be observed:

(i)     LNAV and VNAV will be active;

(ii)    The FMA will display FMC SPD / LNAV / VNAV PTH;  

(iii)   The annunciators on the MCP - LNAV, VNAV & CMD A/B will be illuminated;

(iv)   The speed window located on the MCP will be blank (no speed displayed); and,

(v)    LNAV/VNAV will be displayed in white text on the PFD.

ATC request a descent from FL150 to FL120.

DESCENT Using ALT INTV (descent from FL150 to FL120)

Dial into the altitude window on the MCP the new altitude (FL120). 

CDU cruise page showing 12000 in scratch pad.  Selecting line select 1 left (LS1L) will update the CDU to the new Flight Level

Notice the altitude display above the altitude tape on the PFD has changed from FL150 to the new altitude of FL120.   Also note that the VNAV annunciator light on the MCP remains illuminated - in this case VNAV is armed.  ALT INTV takes precedence over VNAV.  

Select (press) ALT INTV button on the MCP and the FMA will annunciate FMC SPD / LNAV / VNAV PTH.   The aircraft will descend at 1000 fpm (default descent speed) until FL120 is reached.  

If you cross-check the Cruise Altitude in the CDU (INIT PERF/PERF/CRZ ALT or CRZ key/CRZ ALT), it will display the original Cruise Altitude of FL150.  The FMC has NOT automatically updated the Flight Level to the lower altitude – this is normal and not a fault.  

If you want to remain at FL120, you will need to manually update the Cruise Altitude in the CDU (INIT PERF/PERF/CRZ ALT), or (CRZ key/CRZ ALT) and press the EXEC key.  

Important Points:

  • When the CDU page is open on CRZ (CRZ key), it will display in the scratch pad any change to the altitude in the MCP.  This provides a ‘shortcut’ to insert the new flight level should it be desired to make it permanent.  All that is needed is to press the CRZ/CRZ ALT (in the CRZ page) and the FMC cruise altitude will be updated.  The altitude in the LEGS page will also be updated.

  • By default, Altitude Intervention will always maintain a vertical descent at 1000 fpm.

Returning to Original Flight Level

To return to the original Flight Level (FL150), dial into the MCP the previous Flight Level (FL150) and press ALT INTV.  The aircraft will ascend to FL150.  

Important Points:

  • The FMC will NOT automatically update the Flight Level to the lower altitude.  If desired, this will need to be done manually.

  • When returning to the original Flight Level, VNAV will not engage unless the original Flight Level (FL150) is dialled into the altitude window of the MCP.  For VNAV to be active, the Cruise Altitude in the CDU and the altitude set in the MCP must be identical.

  • ALT INTV takes precedence over VNAV.  The VNAV annunciator on the MCP will remain illuminated and  VNAV will be in armed mode (when ALT INTV is selected).

  • To determine if VNAV is the active mode (or not) the FMA display must be consulted – not the annunciator light on the MCP.

  • U10.8A bring some important changes from earlier U releases.  If there are no altitude restrictions, pressing ALT INTV will automatically update the altitude in the CDU to the lower selected altitude.  However, if an altitude restriction is present the lower altitude will not be updated.

ASCENT Using ALT INTV (ascent from FL120 to FL150)

The ALT INTV button operates a little differently when you ascend.   For a start, it automatically replaces (updates) the Flight Level (CRZ ALT) in the CDU.  It will also update the altitude in the LEGS page in the CDU. 

The FMA will annunciate  N1 / LNAV / VNAV SPD during the climb phase of the flight, changing to FMC SPD / LNAV / VNAV PTH when the new flight level is reached.  When climbing using ALT INTV, the thrust mode uses N1.

Important Points:

  • When a Flight Level of a higher altitude is dialled into the altitude window and ALT INTV selected, the new Flight Level will be updated in the CDU.

  • U10.8A bring some important changes from earlier U releases.  If the selected MCP altitude is BELOW any altitude restriction, then that restriction will be DELETED.  Also, altitude restrictions will be DELETED if they are between the current altitude and the selected MCP altitude (when ALT INTV is pressed).

  • If ascent and descent do not function correctly. In the first instance consult the FMS software for the U version in service.

Considerations When Using ALT INTV

When using ALT INTV, several variables that relate to the altitude constraint (s) will change, depending upon whether you are in VNAV climb, cruise or descent.  Rather than rephrase what already has been written, I have scanned the appropriate page (below) from the Cockpit Companion written by Bill Bulfer.

Using ALT INTV and SPD INTV During a VNAV Approach Phase

ALT INTV is a very handy tool, if during an VNAV approach, the flight crew fail to change the altitude in the MCP to the next lowest altitude constraint.  

To demonstrate, the aircraft is flying a published STAR that will join an VNAV approach.  VNAV and LNAV are active and the flight plan has several altitude and speed constraints.  To meet these constraints, the crew must update the MCP altitude to the next lowest altitude (displayed in the LEGS page of the CDU) prior to the aircraft crossing the constraint.

If the crew fail to update the MCP to the next lowest altitude constraint, then the aircraft will transition from descending flight (VNAV PTH) to level flight (VNAV ALT).   In this situation a crew could engage LVL CHG or V/S,  however, doing so would deselect VNAV.  

A simpler solution is to change the altitude in the MCP window to the next lowest altitude constraint (or MDA) and press ALT INTV.  This will command VNAV to descend the aircraft, at a variable descent rate, to meet the required constraint.   By using ALT INTV, the aircraft will remain in VNAV.

Additionally, SPD INTV is a straightforward way to control the speed of the aircraft during the approach while maintaining VNAV.  Company policy at some airlines insist that Speed Intervention be used approximately 2 nautical miles from of the Final Approach Fix (FAF).

Reliability of ALT INTV in Descent Mode - ProSim-AR

ProSim-AR (Version 1.49) exhibits difficulty in holding a lower altitude level when ALT INTV is used.

The Boeing system is designed that once the V-Path is intercepted, the Flight Director (FD) cross hairs maintain the new altitude by pitch.  In ProSim-AR this pitch is often difficult to hold and a resultant pitching of the aircraft (up and down) occurs as the system attempts to hold the lower altitude.  When using LVL CHG or V/S this does not occur.  Note that this behaviour does not occur when using INTV ALT to ascend.

It is not certain if this behaviour is common only to my system or is more widespread; but a way to solve the issue is to either:

(i)   Use an alternate descent mode; or,

(ii)  Manually change the altitude values in the CDU (INDEX/PERF/CRZ ALT), or (CRZ key/CRZ ALT) and press EXEC.

Procedure (ii) manually changes the Cruise Altitude (CRZ ALT) to the lower altitude in the CDU.  This causes the command logic to switch from the logic that commands Altitude Intervention to the logic that commands altitude in thr FMC.  The aircraft will not pitch and will be stable.

The developers at ProSim-AR are continually tweaking these variables.  In future software releases (post version 221.b12) this issue may well be rectified.

Final Call

There are many of reasons an aircraft will need to alter altitude and/or speed; be it to divert around a localized weather event, or to abide by an Air Traffic Control directive.  Whatever the reason, often the changes are short-lived and a return to the original altitude/speed constraint imminent.

In these situations Altitude and Speed Intervention enable the aircraft to easily and quickly transition between Flight Level changes whilst VNAV is active.   Furthermore, the use if this functionality can minimise the time spent in the ‘heads down’ position during the high-task descent and approach phase of a flight.

In this article, I have explained the Altitude and Speed Intervention functionality of the Boeing 737.  I also have documented "work-arounds" should VNAV not function as anticipated. 

Acronyms and Glossary

  • Annunciator - A push button to engage a particular mode – often has a light that illuminates

  • ALT INTV - Altitude Intervention

  • CDU – Control Display Unit (display screen and keyboard to input data into the FMC)

  • Flight Level – Altitude that the aircraft will fly at (set in FMC)

  • FMA – Flight Mode Annunciator

  • FMC – Flight Management Computer  (part of the Flight Management System)

  • FMS – Flight Management System

  • LNAV – Lateral Navigation

  • MCP – Mode Control Panel

  • PFD – Primary Flight Display

  • SPD INTV - Speed Intervention

  • VNAV – Vertical Navigation

Alternate Use for OEM Rudder Pedal Circuit Breakers

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OEM circuit breaker switch.  The two connectors on the rear of the switch are very easy to connect to an interface card for push/pull functionality

The picture at left is of an OEM circuit breaker that has been removed from an OEM rudder crank unit.  The front plate of the control mechanism has several circuit breakers on the Captain and First Officer-side of the flight deck.

Although connection of the circuit breakers, to the original functionality that was assigned to the switch in the aircraft, is not necessary (unless wanted), there is no reason why the circuit breakers cannot be used for additional functionality outside of the simulator environment.   Many enthusiasts have specially made panels that reside in the center pedestal to address such a need. 

The circuit breakers are basically an on/off push/pull switch.  Each switch can be easily wired to a standard interface card, such as a Pokeys or Leo Bodnar card, and then configured in ProSim-AR to a particular function.  If using FSUIPC, the functionality of the switch can be assigned to any on/off function.

For example, using FSUPIC (buttons) it is possible to assign each circuit breaker to a simulator function such as: pause, sim acceleration, jetway extension, etc.  The list is almost endless.

In my simulator, I have the Captain-side circuit breaker switches configured to simulator pause and simulator time acceleration.  These commands are readily accessible within the FSUIPC framework.

The circuit breaker switches are aesthetics, therefore, configuring the switches to regularly used commands is a way to minimize keyboard usage, and de-clutter the flight deck.

This post is not exactly a thrilling entry. 

I am working on three articles at the moment and a detailed review of the SimWorld MCP and EFIS.  I also am slowly updating previous articles to take into account changes to technology and ideas.

I hope to have these ready for publishing in the not to distant future.   Best,   F2A

OEM Rudder Crank Unit

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OEM rudder adjusting crank unit installed to Captain-side kick-stand.  The upper portion of the stick shaker can be seen in the foreground

The two OEM rudder adjusting crank units have been sitting in storage for considerable time, and I thought it was time to add them to the simulator and replace the very poorly made and ‘cheesy’ reproductions.

The unit is not a small item that can easily be attached to the lower kick stand of the Main Instrument Panel (MIP).  Each crank handle attaches to a 8-inch-long box, that houses the various circuitry, cabling and a dozen or so aircraft circuit breakers. 

Connection to the aircraft’s system is via two Canon plugs at the rear of the unit, while movement of the pedals forward or aft is facilitated by a long metal cable that connects to the rear of the handle.

The unit is not light-weight and weighs in at just over 1 kilogram.

The rudder crank handles do nothing other than add to the aesthetics of the simulator.  However, if wanted the various circuit breakers can be connected to an interface card (I will not be doing this).

rudder adjusting crank unit (prior to cleaning).  The long metal cable that connects to the rear of the handle (enabling the forward and aft adjustment of the pedals) has been removed.  The white crank handle hangs loose and needs to be attached to the box using plastic fasteners (empty holes).  The black circular pull on/off circuit breakers can be seen below the white handle

Installation to MIP

There are several methods that can be used to install the mechanism to the Main Instrument Panel (MIP).

If you are using an OEM MIP, then connection of the mechanism to the kick-stand is a matter of using the existing bolts and placement holes.  Fitment to a reproduction MIP is accomplished differently and depends upon how the MIP has been fabricated. 

I fabricated an aluminium cradle (saddle) that is attached by two nuts and bolts to the lower portion of the kick-stand (under the kick-stand out of sight).  The rudder adjusting crank unit slides into the cradle and a small screw holds the unit in the correct place.  A similar assembly could easily be made from wood or ABS plastic and painted Boeing grey.

The method of attachment differs to the way the unit is attached in the real aircraft  (classic or Next Generation).  I have abutted the upper section of the unit against the lower kick-stand.  In the real aircraft the mechanism is attached by a metal mounting bracket and screws.  As stated above, the type of MIP you are using and how it's fabricated indicates the best way to attach the unit (unless you want to bastardise the MIP).

737 Next Generation rudder adjusting crank (courtesy @ Karl)

Classic (500 series)

The rudder adjusting crank I have installed is from a classic 500 series airframe.  The difference between the classic and the Next Generation is minimal, however the method that the mechanism is attached to the lower kick-stand differs considerably. 

The classic is as shown in the above two images while the Next Generation, shown at left connects directly to the kick-stand via a a series of brackets that form part of the lower kick-stand structure. 

For those who are interested in a reproduction unit, AeroSim Solutions in Australia has a reasonable facsimile.

Read about an alternate use of the circuit breakers.

  • Updated 25 June 2020.

Conversion of OEM CDU - Part One

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Completely gutted.  All unnecessary and unusable electronic components have been removed

One of the more advanced projects is the conversion of two OEM Control Display Units manufactured by Smiths.  The two CDUs came from a Boeing 500 series airframe that was retired from service in 2008 due to United Airlines decision to adopt the Airbus A-320.  A chronometer located on the rear of each unit, shows the hours of use - one unit has 5130 hours while the other has 1630 hours.

The Control Display Unit (CDU) is the interface that the flight crew use to access and manipulate the data from the Flight Management Computer (FMC); it's basically a screen and keyboard.  The FMC in turn is but one part of a complex system called the Flight Management System (FMS).  The FMS is capable of four dimensional area navigation.  It is the FMS that contains the navigational database.  Often the words CDU and FMC are used interchangeably.

In this article I will discuss some of differences between OEM and reproduction CDUs. In addition to explaining some of the advantages that using an OEM unit brings.  A second article will deal with the actual conversion of the units to operate with ProSim737.

Port side of CDU with casing removed to show the electronic boards that are secured by lever clips.  Like anything OEM, the unit is constructed from solid component

Construction and Workmanship

The construction and workmanship that has gone into producing anything OEM is quite astounding. 

The CDU is built like a battleship and no amount of use or abuse can damage the unit.  The unit is quite large and heavy.  I was surprised at the eight, a good 6 kilograms.  Most of the weight is made up by the thick glass display screen  CRT, and other components that reside behind the glass within the sturdy aluminium case. 

A myriad number of small screws hold together the 1 mm thick aluminium casing that protects the internal components.  In addition to screws, there are two special DZUS fasteners, that when unlatched, enable the side of the unit’s casing to be removed for maintenance. 

When the casing of the CDU is removed, the inside is jammed full of components, from the large CRT screen to gold-plated electronic boards that are clipped into one of three internal shelves.

One aspect in using anything OEM is the ease at which the item can be inserted into the flight deck.  DZUS attachments enable the unit, once it has been slid into the CDU bay, to be securely fastened.  I use a MIP manufactured by Flight Deck Solutions and the CDU slides seamlessly into the CDU bay.

Detail of the keyboard and DIM knob.  Interestingly the DIM knob dims the actual CRT screen and not the backlighting

Tactile Differences

Aside from external build quality, one of the main differences you immediately notice between an OEM and reproduction CDU, is the tactile feeling when depressing the keys on the keyboard.  The keys do not wobble in their sockets like reproduction keys, but are firm to press and emit a strong audible click. 

Furthermore, the backlighting is evenly spread across the rear of the keyboard panel with each key evenly illuminated.

Aesthetic Differences – 500 Series and Next Generation

As the CDU dates from 2008, the external appearance isn’t identical to the CDU used in the Next Generation airframe, however, it is very close.

Main Differences:

  • The dim knob is a slightly different shape.

  • The display screen is rounded at the corners od the screen (the NG is more straight-edged).

  • The absence of the horizontal white lines located on the inside edge of the display frame bezel.

  • The display screen is different (cathode ray tube (CRT) in contrast to liquid crystal display (LCD).

  • The illumination is powered by bulbs.

In terms of functionality, as this is controlled by software (ProSim737) the functionality is identical.  This also holds true for the font type and colour.

To an absolute purist, these differences may be important, and if so, you will have to contend with a reproduction CDU, or pay an exorbitant amount for a decommissioned NG unit. 

OEM CDU installed to MIP functioning with ProSim737

Conversion for use with ProSim737

There are many ways to convert a real aircraft part for use in Flight Simulator.  By far the most professional and seamless is the integration of the real part using the ARINC429 protocol language (as used in the real aircraft).  However, using ARINC429 is not a simple process for all applications.  Not too mention that you often must use high voltage AC power.

For the most part I’ve used Phidgets to convert real parts, however, in this conversion I wanted to try a different approach.  I’m going to liaise with an Australian company called Simulator Solutions.  This company specialises in converting high-end electronic components used in commercial flight simulators, and manufactures an interface board that should enable seamless conversion of the CDU.

Glossary

  • ARINC 429 –  A standard used to  address data communications between avionics components.  The most widely used  standard is an avionics data bus.  ARINC 429 enables a single transmitter to communicate data to up to 20 receivers over a single bus.

  • OEM - Original Equipment Manufacture (aka real aircraft part).

Troubleshooting Power Management Settings and Solving USB Disconnects

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High-speed 5 volt powered USB hub.  This hub resides in the Throttle Interface Module (TIM).  Note ferrite choke

Remember when all that was required to run flight simulator was one display monitor, joystick and a keyboard – those days are long gone.   

Depending upon the level of system complexity, a flight simulator may require a dozen or more ports to connect peripheral items to a server or client computer (s).  Historically, connection of peripherals has been via USB.  

USB is an acronym for Universal Serial Bus and, generally speaking, if only a few peripherals are attached to a computer, there usually is not a problem with communication between the computer and the attached device.  However, as interface cards and peripherals become more complicated and numerous, there is a propensity for disconnects to occur more frequently.  A USB disconnect usually announces itself by the sound card playing the ‘ding-dong’ sound as the peripheral disconnects itself from the computer.

Guidelines (golden rules)

There are several ‘golden rules’ to remember when using USB.

(i)      Try and keep all USB cables as short as possible;

(ii)     Do not join USB cables together;

(iii)    Always use quality USB cables with quality connectors;

(iv)    Do not ‘kink’ the USB cable or wrap the cable so tightly that the wires are at a 90-degree angle;

(v)     Do not lie USB cables beside one another so they are touching, but maintain some space between them;

(vi)     Use a USB cable fitted with noise limiting nodes (NLN);

(vii)    Use a USB cable/port that is rated at the highest output (USB 3 or above);

(viii)   For multi USB connections use a quality powered USB hub; and,

(ix)     Try to maintain space between USB cables and power cables.

Ferrite choke on USB cable

Noise Limiting Node (NLN)

A noise limiting node (NLN), also known as a 'ferrite choke' is a small cylindrical node that sits at each end of a USB cable.  Briefly explained the nodes are made from a solid ball of ferrite which is magnetic and therefore quite heavy.

The purpose of the NLN is to stop electromagnetic interference (EMI) transferring from the peripheral to the computer.  EMI can be produced from any number of peripheral items and a USB cable running between the peripheral and the computer acts as an antenna, picking up and transmitting EMI current.  The current can, but not necessarily always, cause havoc with either the operation of the peripheral or the computer itself.  

Adding USB Ports

As the number of add-on peripherals increase, the number of available ports falls short and additional USB ports need to be added to the computer.  Additional ports can easily be added to a computer via a PCE card which enables (on average) an additional 4 USB ports to be added to your computer.  A PCI card is attached to your motherboard.

Power Requirements

One of the main reasons that USB disconnects occur, relates to the power that is available to the computer’s USB port.  Often the power requirements of the device will be greater than that provided to the USB port; this causes a disconnect.  Additionally, depending upon your computer, it is not uncommon for power to fluctuate between USB ports as the computer’s motherboard directs power to various processes.

Depending upon how your system is set-up, when several devices 'come on line' a minor spike can be generated.  Often, this spike can momentarily exceed the amperage rating of the USB port.  This can cause a disconnect to occur.

It’s important to understand that not all USB ports are made identical.  In general, the ports on the rear of the computer are part of the computer’s motherboard; these ports are rated as high power ports.  However, USB ports that are not part of the motherboard, and usually located on the front of the computer may not receive the same power rating.  

Often a supply company will provide a computer will a dozen or so USB ports, however, to save money will choose to use what is called a ‘front panel USB header’ which has a small piece of circuitry that acts as a hub.  In this case, the power to the front panel USB is reduced.  Furthermore, it is probable that these ports may not be USB 3 and if used for a high-demand peripheral will cause a disconnects to occur.

USB Hubs

Another strong recommendation is to use a high quality powered USB hub rather than connecting several USB cables directly to a computer.  A powered hub should be used rather than an unpowered hub as the former provides its own direct power source which is usually rated at a higher amperage than the computer’s USB port.  

The interface modules that form the core of my simulation system have one or two powered hubs installed to the module.  The interface cards are then connected by very short USB cables to the hub.  A high quality USB cable (with a NLN) then connects the interface module directly to the computer.

Recommended USB Hubs:

  • The USB hubs I use are Belkin powered 5 and 7 port USB hubs (Belkin F5U237-C). The C refers to the connector on he USB cable.

Screen grab of Windows 7 PMS.  Windows 10 is similar

Windows Power Management Settings (PMS)

Not all USB peripherals will be required at all times.  Often a device will not need to communicate with the computer until something is required – such as a change to a radio frequency, an input from the control column or a key press to the MCP or CDU.

Windows has a nasty habit of ‘putting to sleep’ a USB connection that is not being used.  It does this to save power.  It is very imperative that you ensure that all power saving modes are turned off with regard to USB.  

To do this open your control panel and search for device manager.  Scroll down until you find Universal Serial Bus.  Under this tab you will find all the USB ports that you have attached to your computer.  Open each in turn and check the power management settings and ensure they are turned off.

Troubleshooting USB Disconnects

It is paramount to try and discover which peripheral is causing the disconnect.  The easiest way to troubleshoot a disconnect issue is to remove ALL the USB cables from the computer, and then one by one re-connect the cables to the allocated port and test.  Make sure you switch your computer off and on as you add each of the cables in turn.  Hopefully, you will eventually discover which cable/device is causing the issue.  The problem device will generate ‘ding dong’ if a secure connection is not possible.

If USB disconnects continue, try swapping the cables between different USB ports on the computer.  The disconnect issue maybe caused by the USB port/cable combination you are using.  As mentioned, not all USB ports have the same amount of power/amps available to them. 

Try to place peripherals that require minimal power, such as a mouse or keyboard, on lower-powered USB ports, and place more energy-requiring peripherals on powered hubs; perhaps only a few devices on the one hub.  Doing this will ensure that the hub will always have enough power (amps) to power the devices attached (cancelling out possible spikes as discussed above).  

A potential problem can be located with the USB cable, cleanliness and tightness of USB connections (including any USB hub), and loose wiring (especially if connectors have been used to secure the wiring).

Clean the USB connections with a quality cleaner to ensure cleanliness and make sure the USB connectors are tight.  If the connectors need tightening, this can easily be done by pushing the small tabs inward on the female USB connection.

Final Call

Hopefully, if you apply the above-mentioned suggestions USB disconnects will cease.  However, you will eventually reach the limit of USB capability, and at this point the use of Ethernet should be investigated to augment, or to replace the reliance on USB.

This article is but a primer.  I am not an IT expert and welcome any comments.