Boeing 737 NG Master Caution System ('six packs') Installed and Operational

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There is no mistaking the clarity and brightness of an OEM unit.  This is the Captain-side Master Caution System (MCS)

In my opinion, many simulators fall short when it comes to replicating the Master Caution System (MCS).  Most companies offerings are cheesy-looking in appearance, exhibit the incorrect colour hue, and lack the brightness seen is the OEM unit.  

This post will examine the use of Master Caution System and explain how the OEM items were fitted to the simulator and interfaced with ProSim737 avionics suite.  It will also briefly compare the real unit to the reproduction unit.

Click images for larger view.

Boeing Master Caution System (MCS) - Overview and Use

The Master Caution System (MCS) was developed for the Boeing 737 to ease pilot workload as it was the first Boeing airliner to be produced without a flight engineer. In simple terms the system has been designed to be an attention getter - the brightly illuminated version of a flight engineer’s 'barked' out commands…

The MCS comprises four annunciators (warning buttons) and two System Annunciator Panels (six packs) located on the Main Instrument Panel (MIP) in the glareshield on both the Captain and First Officer sides.  

The location of the annunciators and the intensity of illumination is important.  If an annunciator should illuminate, the positioning and brightness is such, that there is minimal possibility of a flight crew ignoring the warning.  Whilst the warning buttons are duplicated on both sides of the MIP, the annunciation panels provide different 'cautions' for the Captain and First Officer.  

Fire Warning and Master Caution annunciators showing The detailed engraving on the legends

Fire Warning (Fire Warn) Annunciator

If a fire is detected in the APU, main gear well, cargo compartment or during a fire warning (or system test) in either engine, the Master Fire Warning annunciator (button) will illuminate RED.  The fire bell, and if on the ground the remote APU fire warning horn will also activate.  

Depressing the button from either the Captain or First Officer's side with a firm push will extinguish the button’s light and silence the audible fire bell and APU warning horn, in addition to resetting the system for additional warnings.  Pushing the fire warning bell cut-out switch on the overheat/fire protection panel (fire suppression module or fire handles) accomplishes the same action.

Master Caution Annunciator

The Master Caution annunciator (button) is coloured AMBER.  The button will illuminate when a system annunciator (six pack) has been triggered indicating a fault has been detected within the aircraft systems.

Depressing the button with a solid push (Captain or First Officer side) will extinguish the button’s light and reset the system for additional master caution conditions.

System Annunciator Panel ('six packs')

There are two System Annunciator Panels, one on the Captain side and one on the First Officer side.  Each light plate has six different AMBER coloured 'cautions' which are arranged such that the 'cautions' are in the same orientation as the overhead panel.  For example, FUEL is bottom left.  

Components of the Master Caution System:  Two duplicated Fire Warning and Master Caution buttons and the two System Annunciator Panels (six packs).  The diagram shows the various cautions that a flight crew can expect to observe (image copyright FCOM).  The MCS is identical for all Boeing series airframes 600 through 900 including the Boeing Business Jet (BBJ)

The display annunciations relate a specific aircraft system.  The following are displayed on the Captain-side panel: FLT CONT, IRS, FUEL, ELEC, APU and OVHT/DET.  The displays for the First officer side panel are: ANTI-ICE, HYD, DOORS, WNG, OVERHEAD and AIR COND.

If a master caution condition exists, the Master Caution light will illuminate AMBER along with the appropriate system annunciator.  Likewise, if a caution exists and is displayed on either six pack the Master Caution button will illuminate.

To extinguish the System Annunciator display, the Master Caution button should be firmly depressed.

Self-Test and Recall

The System Annunciators have a self-test and recall function.  Firmly pressing and holding either light plate will cause all annunciation lights to display (self-test).   To recall the last displayed 'caution', the light plate is pressed once and released.  After release the system annunciator will display whatever "caution" was last detected.

There is little argument that the OEM Master Caution System exceeds the quality of reproduction units.  This is the MCS from a top shelf manufacturer.  Compare thsi with the OEM counterpart. Reproduction units could be easily improved if they used a number of high intensity LEDS aligned in an array so that the light had better coverage

Reproduction Verses OEM

Broadly speaking, there is a large gap in quality between reproduction MCS units and the OEM version.  

For the most part, reproduction annunciators are very easy to depress - a tap of a finger will deactivate a warning or recall a ‘caution’.  The legend is printed rather than lazer engraved and the colour of the light is often an incorrect colour hue which lacks the brightness of the real unit.  The last point is caused by low voltage LEDs which are not bright enough and do not have an adequate throw of light to illuminate all of the legend.  Furthermore, reproduction units are for the most part made from plastic, rather than longer lasting aluminium.

This said, some highly priced units do replicate the OEM part very well but they do cost upwards of $450.00 USD (see Fly Engravity).

In contrast, the OEM unit has engraved legends that are very distinct and easy to read, require a firm press to engage, and are very bright.  OEM units use 28 Volt bulbs which burn very brightly.

Not Just A Finger Tap - Firmness in Operation

An OEM annunciator requires a bit more force to depress the button in comparison to a reproduction unit.  I'm uncertain if this is due to the strength or weakness of the internal spring mechanism or as I've been lead to believe, is a built-in safety feature; thereby minimising the chance of a flight crew accidentally depressing and cancelling an annunciator ‘caution or warning’ with a light tap or brush of the of the finger or hand.

Classics Verses Next Generation (NG)

Both airframes incorporate the Master Caution System; however, the classics use different display cautions for the system annunciators. I believe there are five 'cautions' on the classic in contrast to six on the NG (600, 700, 800 & 900).  The fire and master caution annunciators are identical on all Boeing airframes.

Interfacing and Power Requirements

To interface the unit requires a Phidget 0/16/16 interface card while the power to illuminate the bulbs is from a 28 Volt power supply.  A 0/16/16 card provides 16 inputs and 16 outputs which allows complete coverage of all functions remembering some functions duplicated on the Captain and First Officer-side have wires placed into the same input terminal. The duplicated items are the fire and master caution annunciations.

Each of the four annunciators has three terminals.  A multimeter set to conductivity or beep mode is used to determine which terminal connects to which button press. 

  • To learn how to use a multimeter, read this article.

The System Annunciator Panel (six pack) is a little more convoluted as it has a recall facility and has different cautions between the Captain and First Officer units.  However, with a little diligence it’s possible to work out the terminal and wiring sequence.

Anatomy of a System Annunciator (akasix pack)

Each unit is made up of three parts:  the actual annunciator, the light plate (which incorporates the legend), and a rectangular housing that I call the cigarette packet. The housing is attached to the annunciator by two hex screws.

Light plate removed from housing and rear terminals.  Note individual pins for specific display cautions and "clam shells" for connection

The light plate has a number of pins that connect with the annunciator base, and on the rear there are eight terminals (lower image) each connecting with a specific terminal.

If you remove the outer casing, a circuit diagram has been stenciled to the unit.  It’s trial and error using this diagram to determine the correct pin outs for the terminals, but once known it’s only a matter of connecting the various wires from the the terminals to the 0/16/16 card.

Eight terminals.  The outer edge of the hex nut can easily be observed on the upper left side of the annunciator

It’s important to note that if removing or loosening the outer cigarette-style housing, a hex screw located at the corner edge of the unit will need to be loosened. 

Phidgets 21 Manager

The Phidget 21 Manager is provided by Phidget and can be downloaded from their website.  This software will, when a Phidget card is connected, register that card and its distinctive number. 

Opening the Manager and then selecting the card number ID tag will allow you to see what inputs and outputs you have wired and assigned to whatever item you have connected.  You will also be able to easily test any output.

Configuring in ProSim737

Once the pin outs have been correctly determined, configuring in ProSim737 is very easy.  Open the configuration tab and select the indicators menu (tab).  Next find the appropriate names (DOORS, ELEC, APU, ANTI-ICE, etc) and in the drop down box assign the correct Phidget card and output number.

Installing to the Glareshield

Main Instrument Panels (MIPS) manufactured by different companies are rarely identical; each MIP has subtle differences – some are easier to install OEM items to than others.

Detail of Master Fire Warning annunciator showing manufacturer name and threaded button with hexagonal attachment nut.  different manufacturers produce slightly different shaped bodies

Reproduction annunciators are usually secured to the glareshield by screws; however, OEM parts often require retrofitting to allow the item to be fitted correctly. 

In the case of the FDS MIP, a backing plate made from ABS plastic was crafted to fit into the gap where the fire warning and master caution buttons reside; the plate was secured to the glareshield by self-tapping screws.

Two holes were then carefully drilled at the correct distance to allow the circular shaft of each button to be fitted through the plastic.  Once the button was sitting proud in the correct position, the screw and nut assembly was tightened against the backing plate.  

The annunciators are not designed to sit neatly side by side in the glareshield; they can be twirled to any orientation; therefore, it’s not necessary to be perfect in the alignment of the drill hole – just very close!

Securing the system annunciators to the MIP was slightly more problematic and involved using a spacer between the outside of the housing and the gap in the glareshield.  The spacer expands as you push the six pack into position, and it’s a matter of enlarging the spacer to secure the unit in the correct position.  This said, the method used is not optimal and a more secure method needs to be developed.

Video (Captain-side only)

A short video demonstrates the brightness of the buttons and display cautions.

The annunciator light plate displayed in the video is not in the best condition; it is common for airlines to place clear tape over the legends to protect them.  This did not concern me at the time, as six packs are scarce to find.  However, I have since found four buttons in better condition and will soon exchange them.

  • For those interested, to silence the fire bell in the video, I used the bell cut-out switch on the fire suppression module rather than depressing the Fire Warning Annunciator, which would have accomplished the same task.

 

737 Master Caution System and six packs

Acronyms and Glossary

  • Annunciator – A single coloured light or group of lights used as a central indicator of status of equipment or systems in an aircraft. Usually, the annunciator panel includes a main warning lamp or audible signal to draw the attention of operating personnel to the annunciator panel for abnormal events or conditions.  To annunciate means to display or to become audible.  Annunciators often are called KORRYS (KORRY is the name of a manufacturer).

  • Cautions – Annunciations from the System Annunciation Panel in amber colour.  For example, DOORS, APU and ELEC.  An annunciation 'caution' triggers the Master Caution Warning light.

  • FDS – Flight Deck Solutions

  • Light Plate - the actual forward portion of the annunciator separated from the rear section and the housing.

  • Legend – The portion of the light plate that includes the engraved display (for example, ELEC or DOORS)

  • MCS – Master Caution System incorporating: Fire Warning, Master Caution Warning and two annunciator panels (six packs)

  • MIP – Main Instrument Panel

  • OEM – Original Equipment Manufacture (real Boeing part)

  • Phidget 21 Manager – Configuration software to use a Phidget card

  • 'Six Pack' – Nickname for System Annunciator Panel

  • System Annunciator Panel (SAP) – Light plate with six 'cautions' and recall facility (NG only).  Also known as 'six pack'

Update

UPDATE ON 2015-07-29 13:10 by FLAPS 2 APPROACH

Captain side straight-through cable connector mounted beneath the glare wing. The colour-coded internal wiring of the lumen can be seen.

The white terminal block facilitates connection of the the MCS with the Lights Test functionality (Lights Test toggle located on the MIP).  To the terminal block, a wire connects directly to a Lights Test Busbar located in the center pedestal.  The busbar then connects directly with the OEM lights test toggle switch. The brackets are made from ABS plastic

In June 2015, the wiring design for the simulator was changed, and the annunciators were rewired to facilitate conformity with the wiring of other OEM parts.  The Captain and First Officer annunciators were separated and wired directly to a Phidget 0/16/16 card. 

To ensure that the wiring was easily identified, wiring for the Master Caution System was color-coded to avoid any confusion with the wires that have been used to wire the AFDS units.

The new wiring design called for each MCS to be independently wired and separated from the other.  Each system has the wires budded into a dedicated, colour-coded lumen which is then connected to a serial port connector mounted to a bracket.  The bracket is attached to the underside of the glare wing at the rear of the MIP glareshield.  The connectors have straight-through cables that snake behind the MIP to mate with their respective connectors on the SMART module.

Main Instrument Panel (MIP) - Seeking Accuracy in Design

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OEM 737-800 MIP AND COMPONENTS (Shawn from Airdrie, Canada, 737NG Panel (4559309701), CC BY-SA 2.0)

A reproduction Main Instrument Panel (MIP) may appear identical to its OEM counterpart, but there can be there can be subtle differences depending upon which company you purchase a MIP from. 

The disparity may not be important to individuals who decide to use a full reproduction flight deck from the same company. However, problems will soon surface if mixing parts from other companies’ or using OEM components.

The following relate to all reproduction MIPS.

The Bezel. The bezel is the frame that surrounds the display units (DUs).  In the real aircraft the bezel forms part of the display unit, which is why the bezel breaks open in the lower area; to allow access to and removal of the unit. 

If you carefully look you will note there are no screws that hold the bezel in place to the MIP.  Quite a few manufacturers use Phillip head screws in each corner of the bezel to attach the bezel to the MIP. 

In the real aircraft the bezel is made from machined aluminum.  

Landing Gear Lever.  The real aircraft has a smaller knob than the one currently used by Flight Deck Solutions. The landing gear knob in the real aircraft is translucent.  Further, when the landing gear is in the down and locked position, the red trigger located on the gear shaft completely recesses between the two half-moon protectors and the trigger.

Fuel Flow Reset Switch. The real aircraft uses a switch/toggle with a larger defined and bulbous-looking head, rather than the standard-style toggle most manufacturers use.  The OEM toggle is also very specific in operation (3 way pull & release). 

The knobs used on the MIP. These knobs are called general purpose knobs (GPK) and it's uncommon for a reproduction knob to look identical to an OEM knob.  OEM knobs present with curved rather than straight edges and have the grub screw located in a different position to most reproductions.  Many reproduction knobs have the grub screw located at the rear of the knob. 

Additionally, OEM knobs have an inside metal shroud (circular metal retainer) and a metal grub screw thread, both important to ensure operational longevity of the knob; reproduction knobs usually do not have this.  The metal shroud can be important as it increases the longevity of the knob as it stops the acrylic from being worn down over time with continual use.

The Next Generation also has a backlit, black coloured line that runs adjacent to a translucent line on the front of the knob; at night this line is backlit. Most of the replica knobs have a black line which is a transfer (sticker) that has been hand applied to the knob.  Stickers and transfers often lift and peel away, and hand application is often haphazard with some transfers straight and others being off-center.

Annunciators (Korrys). The annunciators on most reproduction MIPs use LED technology and may exhibit an incorrect colour hue in contrast to the OEM part.  Reproductions can also be lacking with regard to the legend, as OEM legends are lazer cut and the lettering is very sharp and well-defined. 

Annunciators in the real aircraft are illuminated by 28 Volt bulbs contrasting the low brightness LEDs seen in reproduction Korrys - this alone can make a huge difference in aesthetics.  Finally, the push to test function seen in the real item, to my knowledge, is lacking in reproductions. Be aware that some newer Next Generation airframes may use LEDs in favour of bulbs.

Colour.   Boeing grey (RAL 7011), has a specific RAL colour number; however, rarely is every MIP or aviation part painted exactly the same grey colour; there are sublime differences in shade, colour and hue.  Inspect any flight deck and you will observe small colour variations.  Type RAL 7011 into Google and note the varying shades for a specific RAL number. OEM and reproduction panels both share varied colour hues of RAL 7011.

Dimensions & 1:1 Ratio.  High-end MIPs for the most part are very close to the correct 1:1 ratio of the OEM item and differences, if noticeable, are marginal.  But, less expensive MIPs can have the incorrect dimensions.  It is not only the overall dimensions that are important, but the dimensions of the spaces, gaps and holes in the MIP that allow fitment of the various instruments and modules.

Whilst this may not be a concern if you are using reproduction gauges that came packaged with your MIP, it can become problematic if you decide to use OEM parts.  There is nothing worse that using a Dremel to enlarge a hole in a MIP that isn't quite the correct size.  Worse still, is if the hole in larger than it should be.

Musings - Does it Matter ?

If everything fits correctly into whatever shell you're using, then a small difference here and there is inconsequential.  However, if you are striving for 1:1, then it is essential to know what is fact and what is fiction (Disneyland). 

Important Point:

  • There are many nuisances between MIP manufactures. I have mentioned but a few in this article.

System Simulation is a Priority

As I move more into the project, I realize that many items available in the reproduction market are not identical to the real aircraft; a certain artistic license has been taken by many manufacturers.  This said, while it's commendable to have an exact reproduction of a flight deck, keep in mind that a simulator is primarily a simulation of aircraft systems.

Of course this doesn't mean you throw everything to the wind aesthetically.  To do so would mean you would have an office chair, desk and PMDG in front of you.  Aesthetics are important, as they stimulate by visual cues a level of immersion, that allows the virtual pilot to believe they are somewhere other than in their own home.

If you inspect real-world flight simulators used by aircraft companies, you will quickly note that many of the simulators do not replicate everything, or strive to have everything looking just like the real aircraft.  Simulators are designed for training and whilst a level of immersion must be apparent, replicating aircraft systems takes priority.

Acronyms & Glossary

  • Annunciator - A single coloured light or group of lights used as a central indicator of status of equipment or systems in an aircraft. Usually, the annunciator panel includes a main warning lamp or audible signal to draw the attention of operating personnel to the annunciator panel for abnormal events or conditions.  To annunciate means to display or to become audible.  Annunciators are often called Korrys; Korry is a manufacturer of annunciators.

  • FDS - Flight Deck Solutions

  • Korry – See Annunciator.  A brand of annunciator used in the Boeing 737 airframe.

  • Legend - The plastic lens plate that clips to the annunciator.  the legend is the actual engraved writing on the lense.

  • MIP - Main Instrument Panel.

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

  • RAL - International colour matching system.

Ferrules

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ferrules. They enable easy connection of thin wires to terminal blocks

What are ferrules some of you may ask – no they are not the undesirable neighbours that play loud music and park old cars in front of your house; they are called “feral”… 

A ferrule is a small electrical connector that comes in a variety of different sizes that is very handy when connecting electrical wires.  The metal needle of the ferrule is hollow allowing you to fit the correctly sized wire for maximum connectivity and faithful conductivity.

Solid Connection

1mm red ferrules connected to a terminal block

Building a simulator involves the connection of a multitude of wires to interface cards, power supplies, terminal blocks and other electronic components.  Having a method to easily secure wires that ensures reliability is a great asset.

Whilst you can solder wires to the above items, it is often necessary to remove a wire for testing purposes or to add an additional function to the connection.  Twisting and clamping the wire beneath the screws or under a screw tab while functional is far from tidy, and eventually the wire will become damaged with loose wire strands. 

Loose and damaged wires can translate to poor connectivity leading to frustration when something does not work correctly.

A ferrule can easily be attached to the end of a small wire (22 gauge) and crimped.  The ferrule needle can then be cut to size to fit into an interface card or terminal block.  Ferrules come in a variety of colour-coded sizes and can be used for differing wire gauges.

A special crimper tool is used to crimp' the ferrule in place securing the wire.

I’ll submit that ferrules are not suitable to use everywhere; however, for certain applications they are useful to have in your simulator-building toolkit.

Changing Pilot Automation Dependency

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Cp Flight MCP

Although this website primarily discusses construction and flying techniques of the Boeing 737, I believe it's pertinent to include articles that relate to flying in general and have merit to both real-time aviators and virtual pilots.

This article supplements an article that discusses the Speed, VNAV and Altitude Intervention (INTV) system.

Rather than create a link to an interesting article which may at some stage be removed, I’ve copied the article verbatim below.  The article which came from Aviation Week Space and Technology is a little long, but well worth a read.

How To End Pilot Automation Dependency

It is foolhardy to draw hasty conclusions about accidents. The investigation into the cause of the Asiana 214 Boeing 777-200ER crash at San Francisco International Airport on July 6 is still in its early stages. While it is not clear exactly how crew performance figured into the accident that claimed three lives, we believe that there is no excuse for landing short on a calm, clear day in a fully functioning jetliner. If the NTSB determines that the 777-200ER ‘s engines and systems were working properly, then how could the Asiana pilots have gotten themselves into that jam?

It may be that the crew was acting primarily as “automation managers” and not remaining sufficiently engaged in actively flying the airplane. It would not be the first time that this has been a factor in an accident . In the final 2.5 min. of the flight, the NTSB says, “multiple autopilot modes and multiple autothrottle modes” were inputted—all while airspeed was allowed to drop far below the 137-kt. target. It also may turn out that software rules governing interaction of the autopilot and autothrottle in the 777 are not intuitive under some settings and problematic for landing (see page 25). But that would be no excuse for flying into the ground.

On balance, automation has been a major contributor to the safer, more efficient operation of airliners. But automation has not reached the point where it can handle all contingencies. We have not arrived at the point alluded to in the joke about the crew of the future being a pilot and a dog (the pilot is there to feed the dog, the dog is there to bite the pilot if he touches the controls). So humans must be prepared to hand-fly an aircraft at any point .

For years now, concern has been growing that airline pilot's basic stick, rudder and energy management skills are becoming weak due to over-reliance on automation systems. Pilots have become, in the words of Capt. Warren VanderBurgh of American Airlines dependent upon computers that generate the purple-pink cues on cockpit displays.

There is nothing inherently risky about using automation, he explains in a famous lecture, but there is a paradox about automation that crews must be aware of: In most situations, automation reduces workload. But in some situations, especially when time is critical, automation increases workload. For example, it is harder to rapidly and correctly reprogram a flight-management computer to avoid a midair collision than it is to turn off automated systems, grab the controls and take evasive action on one’s own.

This addiction to automation is particularly troubling because of the rapid growth of the international airline industry in the last two decades, notably in Asia and the Middle East. Many nations, including South Korea, do not have robust general aviation, light air freight and commuter airline sectors where pilots can amass hundreds of hand-flown takeoffs and departures, arrivals and landings before graduating to the cockpit of an Airbus or a Boeing airplane carrying scores of passengers.

In the wake of the Asiana crash , Tom Brown, a retired United Airlines 747-400 standards captain and former instructor of Asiana pilots , said in an email to friends that while he worked in South Korea, he “was shocked and surprised by the lack of basic piloting skills.” Requiring pilots “to shoot a visual approach struck fear into their hearts.”

Other expatriate training pilots who have worked in Asia and the Middle East tell similar stories about lack of basic head-up airmanship skills and preoccupation with head-down button pushing. They can perfectly punch numbers into the flight-management computer but if something unexpectedly crops up late in the flight, such as an air traffic control reroute close to the airport or a runway change, crews may not have time to punch, twist, push and flick all the controls required for the automation to make critical changes to the aircraft’s flight path. And head-down, they risk losing situational awareness.

This pitfall is not peculiar to developing regions, of course. Advanced automation can lull any crew into becoming mere systems monitors.

So what should be done? The automation dependency paradigm must be changed now. Crews must be trained to remain mentally engaged and, at low altitudes, tactility connected to the controls —even when automation is being employed. They should be drilled that, at low altitudes, anytime they wonder “what’s it doing now?” the response should be to turn automation off and fly by hand.

Aviation agencies need to update standards for certifying air carriers. There needs to be a new performance-based model that requires flight crews to log a minimum number of hand-flown takeoffs and departures, approaches and landings every six months, including some without autothrottle use. Honing basic pilot skills is more critical to improving airline safety than virtually any other human factor.

BELOW: Capt. Warren VanderBurgh’s 'children of the magenta' lecture (also viewable on VIMEO and UTube).

 
 

RMI Knobs Installed to Main Instrument Panel (MIP)

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oem rmi knobs

Following on with the theme from my last post, I have replaced the two tear-drop style RMI knobs supplied by Flight Deck Solutions on their Main Instrument Panel with two replacement knobs.

The replacement knobs are highly detailed reproductions of the original 737-800 RMI knobs.  I would like to have used genuine knobs; however, as they are usually attached to an RMI gauge, finding the knobs alone at a reasonable price would be a difficult if not an impossible task.

The knobs have been individually sculptured using clear ABS plastic while the front plate is made from clear acrylic.  The knobs are painted in the correct Boeing grey colour and the black and white stenciling applied directly to the front of the knob.  The knobs can be easily backlit using an LED, although I have yet to do this.  The sizing of the knobs can be determined from information supplied by EHC Knobs located in Farmingdale, New York.

Looking Pretty.....

At the moment the knobs have not been interfaced and just sit there looking pretty. 

In the future, I may interface the knobs by installing micro-buttons and/or a micro- rotary behind each knob.  The knobs will then be connected to an interface card.  However, at the minimum this requires cutting the MIP to create additional space for the location of the micro-switches – something that at the moment I do not want to contemplate.  If given a choice, procuring a genuine OEM RMI gauge would be my preferred option.

In the interim, the RMI Switch Assembly panel discussed in my earlier post will suffice.

UPDATE

Acronyms

  • MIP – Main Instrument Panel

  • RMI – Radio Magnetic Indicator.  The gauge that displays VOR and ADF mode.  Part of B737 NG stand-by instrument cluster

RMI Switch Assembly (ADF/VOR) Installed to Center Pedestal - Flying by VOR & NDB Made Easier

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RMI Switch Assembly dated stamped 1967 (727 or 737-100/200).  RMI switch has been custom fitted to blanking plate

It probably seems an oddity to install into the center pedestal a switch manufactured in 1967 that in all probability was used in a an early model Boeing 737 or more likely a 727.

My reasoning is quite simple. I enjoy flying using VORS and NDBs and the use of the older style 737 switch assembly replicates some the functionality of the stand-by RMI buttons on the MIP. In time, the panel will be replaced when I find OEM 737-800 RMI knobs.

VOR and NDB Flying (NG)

The Next Generation allows tracking of the primary and secondary VOR/NDB with a visual display on the Navigation Display (ND).  The display can be turned on and off from the either the Captain or First Officer side EFIS.  Tuning to the VOR and NDB is accomplished by dialing in the correct frequency on the NAV and ADF radio panels. 

The navigation output is duplicated and shown as dual needle movement on the RMI gauge which is the third gauge within the stand-by instrument cluster.  In the real 737 aircraft, the mode of the RMI gauge can be toggled between VOR 1/2 and ADF 1/2, or a combination, by the small knobs on the front of the RMI that protrude through the Main Instrument Panel (MIP).  

RMI Knobs

It’s unfortunate that many manufacturers of reproduction Main Instrument Panels (MIPS) do not include functionality to these two small knobs and provide only a rough facsimile of an original knob.  

Early Boeing N737 RMI Switch Assembly showing detail of two switches, Canon plug, wiring harness and front panel. The original Canon plug and pib-outs was used in the conversion

Interfacing, Wiring and Blanking Plate

The switch assembly was interfaced to function with ProSim737 using a PoKeys55 interface card.  In my simulator ,the PoKeys card resides in the System Interface Module (SIM) and the five wires from the 737 switch were run through a piece of conduit (plastic piping) beneath the platform to the System Interface Module (SIM) located forward of the MIP.

The five wires correspond to VOR 1/2 and ADF 1/2.  The fifth wire is the common (earth).  Two additional wires (positive and negative) connect to the 5 Volt busbar located in the center pedestal and is used to power the backlighting of the panel.

Canon Plugs - Why Change a Perfect System

The switch assembly included a male Canon plug in very good condition; therefore, it was decided to use the Canon plug system rather than wire separately.  A female Canon plug was purchased from E-Bay and a multimeter, set to continuity mode, was used to determine the correct pin-outs for the plug.

A longer wire harness was made to allow the harness to reach the System Interface Module forward of the MIP.  Using Canon plugs keeps the wiring very neat and allows for an easy disconnect should you need to remove the panel from the pedestal.

oem 727 early 737 cl RMI Switch Assembly installed to the center pedestal.  Selection can be either ADF1/2, VOR1/2 or a combination.  Switches and panel are backlit by 5 Volts which is the standard voltage used in many panels. This panel would never be seen in a 737 Next Generation center pedesta

Blanking Plate

In the Boeing 727 and earlier 737 classic airframes, the RMI Switch Assembly is mounted to the lower part of the MIP (from memory).  In this era (circa 1967) modern-style EFIS units had yet to be developed. 

As such, the switch does not require a lightplate as it is attached to the MIP by four screws.  To facilitate the switch being installed to the center pedestal, a blanking plate had the center portion cut out using a  dremel cutter.  The switch assembly could then by placed in the cut hole and attached directly into the blanking plate via the four screws and the panel secured to the pedestal by DZUS fasteners.

Mapping Functions

To configure the functionality of the Switch Assembly to ProSim737 was straightforward, as the functions have already been mapped within ProSim's configuration menu.  This is one of the major advantages to using ProSim737 as the avionics suite; many functions have been mapped and you do not need to delve into the world of FSUIPC offsets in an attempt to get something working (This what must be done if you use Sim Avionics).

Never on a Next Generation

Although you would never see the panel on a 737 Next Generation aircraft, the switch assembly is very enjoyable to use and makes using the alternate RMI gauge more user friendly - at least until OEM RMI knobs are obtained and configured for use, or an OEM RMI gauge acquired.

Acronyms & Glossary

  • ADF – Automatic Direction Finder

  • Blanking Plate - An aluminium plate used to cover a gap in the pedestal or overhead.  The plate is equipped with DZUS fasteners for attachment to the DZUS rail VOR - Omni Directional Radio Range

  • EFIS – Electronic Flight Instrument System

  • IMM – Interface Master Module

  • MIP – Main Instrument Panel

  • NDB – Non Directional Beacon

  • PANEL – Refers to actual avionics module.  Panel and module are interchangeable

  • RMI – Radio Magnetic Indicator.  The gauge that displays VOR and ADF mode.  Part of B737 NG stand-by instrument cluster

B737-800 NG EVAC Panel - A Nice-looking Panel

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oem 737-800 evacuation panel (evac)

A quick post to showcase an OEM evacuation (EVAC) panel. The panel is usually mounted in the AFT overhead; however, as I am still developing the overhead panels I have temporarily installed it into the center pedestal.  

The EVAC panel’s use needs no introduction – it is triggered by the flight crew if and when evacuation of the aircraft is required / occurring.  A switch in the passenger cabin can be triggered by the cabin crew alerting the flight crew that an evacuation is imminent.  The panel is only used when on the ground (obviously).

The EVAC panel is from a 737-800 and the functionality includes: an arming/off switch, flashing red coloured EVAC annunciation, alarm cancelling pull knob, and a piecing alarm (horn). 

The panel is not connected to any function within Flight Simulator; therefore, an interface card is not required.  A continuity test, using a multimeter, is used to determine which pins in the Canon plug correspond to which switch/toggle/alarm.  The backlighting is powered by 5 Volts whilst the alarm and annunciator is 28 Volts.

Although the panel serves no true function in the simulator, it is a good-looking panel that improves the aesthetics of the center pedestal.  Once the overhead is fully developed the EVAC panel will be removed from the pedestal and placed in the aft overhead panel (the correct location).

The EVAC panel is an airline option.

Below is a video showing the panel’s use.

 

737-800 EVAC panel operation

 

B737-800 NG Fuel Flow Reset Switch - OEM Switch Installed and Functional

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oem 737-800 fuel flow switch can clearly be identified by its bulbous head.  I have observed that on some air frames this switch has a cross hatch design

I have replaced the reproduction Fuel Flow Reset Switch (FFRS) with an OEM switch.  I was not happy with the reproduction switch, which did not function correctly or look anything like the real switch used in the aircraft; the genuine switch is spring-loaded, quite large, and has a bulbous head.  The FFRS is a new switch which was probably destined to be installed into a Boeing Next Generation aircraft.

FFRS Functionality

The Fuel Flow Reset Switch resides on the center forward panel immediately above the central display unit on the Main Instrument Panel (MIP).  The function of the FFRS is to provide information on the fuel flow and fuel used.  The fuel flow/used indications are displayed on the lower display unit (depending on your avionics set-up preferences). 

The switch is a one-pole spring-loaded two-stage three-way momentary toggle switch.  The normal 'resting' position of the switch is in the central (RATE) position.  In this position the display unit indicates the fuel currently being used.  Pushing the switch downwards to (USED) changes the display indication to read the fuel that has been used.  Pulling the bulbous knob towards you whilst simultaneously pushing the switch upwards (RESET) resets the fuel used to zero.  The downward and upward throw of the switch is momentary which means that when the switch is released it will automatically return to its central "resting" position.

The reason the switch is two stage for upwards deployment (pull and push upwards) is for safety; a flight crew cannot inadvertently push the switch to the upwards position resetting the fuel used.

Installation and Wiring

Depending upon what MIP you are using, installation of the switch may require enlarging the circular hole in the MIP. This is to enable the shaft of the OEM switch to fit through the MIP frame and the light plate of the Center Forward Panel.  If the hole must be enlarged, care must be taken to not damage the light plate. 

If the MIP you are using is 1:1 ratio, then the switch should fit through the hole perfectly.  The switch is secured behind the light plate with a hexagonal nut.  This switch fits the FDS MIP without need for enlarging the hole.

The rear of the FFRS has three standard-style screw post connections, each connection being either positive, negative or common (earth).  To determine which throw of the switch does what, it’s necessary to use a multimeter set to continuity (beep mode).  Place the black probe of the multimeter on the central screw post and then place the red probe on either of the other two screw posts.  When you move the switch you will hear an audible beep indicating that function is “active” for that screw post.

diagram 1; fuel flow switch display indications (copyright Boeing fcom)

Interfacing

An I/O card is required for the switch to interface with the avionics suite.  A PoKeys card will suffice; however, I have used a Phidget 0/16/16 card; this card is installed in the SMART module.  This card has been used primarily because it had unused inputs.

Establishing the correct functionality is done within the flight avionics software.  If using ProSim737 it’s a matter of finding the fuel flow switch functions within the switches section of the configuration menu and assigning them.  Failing this FSUIPC can be used.

The FFRS is but a small item; however, many small items make a sum.  By using an OEM switch, you have the correct functionality of the switch in the simulator, and you improve the aesthetics.

The serial/part number for the switch is: MS-24659-27L, or for the non military specification 1TL1-7N.

Acronyms and Glossary

  • FFRS – Fuel Flow Reset Switch (also known as the Used Fuel Toggle)

  • OEM – Original Equipment Manufacturer

  • MIP – Main Instrument Panel

  • Momentary Switch - a switch which can be pushed downwards or upwards and when released returns to a central "resting" position

  • Two-Stage Switch - A switch that requires two events to activate the switch.  For example, simultaneously pulling and pushing upwards on the switch

B737 Throttle Quadrant - Automated Thrust Lever Movement

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Autothrottle arming switch is a solenoid operated switch clearly identified on the main Instrument Panel (MCP).  The switch is linked to the IAS/MACH speed window (adjacent) and to two A/T disconnect buttons located either side of the throttle lever handles. cp flight pro mcp

In this final post dealing with the conversion of the 737-500 throttle quadrant. I will discuss the automation and movement of the throttle thrust levers and touch on some problems that occurred.  I will also briefly discuss the installation and use of potentiometers.  Part of this post will be repetitive as I briefly discussed automation in an earlier post.

Avoiding Confusion - Automation

To avoid confusion, automation refers only to the movement of the two throttle thrust levers in relation to the %N1 output.  These N1 limits and targets are provided by the Flight Management Computer (FMC) and normally are used by the Autopilot Flight Director System (AFDS) and the Auto Throttle (A/T) to maintain airspeed and/or thrust setting.  

Automation and Movement - Interface Cards

Automation is the use of CMD A or CMD B (autopilot) to control the %N1 outputs from the Autothrottle (logic), and motorization is the moving of the throttle levers in unison with %N1 output.  To achieve this seamlessly, two interface and one controller card are used.

Alpha Quadrant Cards (2):  Each  motor controller card has the automation logic programmed directly to the card (via propriety software).  One card controls Auto Pilot CMD A while the other card controls Autopilot CMD B.

Phidget Advanced Servo Card (2):  This card acts as an interface and bridge between the Alpha Quadrant cards and the flight simulator platform used.

The card does not provide movement for the throttle thrust levers; this is controlled by a Phidget Motor Controller card.

Leo Bodnar BUO 836 A Joystick Controller Card:  This card will register in Windows the movement of levers, buttons and switches on the TQ.  Calibration of this card is done first in Windows, then in Flight Simulator (FSX/P3D), FSUIPC or the avionics suite used; for example, ProSim737.

The interface cards are mounted forward of the MIP within the Throttle Interface Module (TIM) and are connected to the throttle unit by custom VGA straight-through cables and to the computer by a single USB cable.

Main Controller Cards

The controller card I have used is not a Phidget card but a specialist card often used in robotics (Alpha Quadrant card).  The software to program the card has been independently developed by a software engineer and does not utilize Phidgets.

The technology used in the controller card is very similar to that utilized by NASA to control their robotic landers used in the space industry.  The technology is also used to control robots used in the car industry and in other mass production streams.  One of the benefits of the card is that it utilizes a software chip (firmware) that can be easily upgraded, reprogrammed, or replaced.  

The Alpha Quadrant cards provide the logic to operate the throttle automation (the movement of the thrust levers) and act as a bridge between the two cards and the avionics suite.

Being able to program each card allows replication of real aircraft logic and systems.  Whenever possible, these systems and their logic have been faithfully reproduced.

oem throttle. toga switches clearly seen

CMD A/B Autopilot - Two Independent Systems

Most throttle units only use one motor controller card which controls either CMD A or CMD B; whichever autopilot you select is controlled by the same card.  

In the real aircraft to provide for redundancy, each auto pilot system is separate.  This redundancy has been duplicated by using two Alpha Quadrant controller cards, rather than a single card.  Each controller card has been independently programmed and wired to operate on a separate system.  Therefore, although only one CMD is operational at any one time, a completely separate second system is available if CMD A or B is selected on the MCP.

Synchronized or Independent Lever Motorization

Synchronization refers to whether the two throttle thrust levers, based upon separate engine %N1 outputs, move in unison with each other (together) or move independently.

In earlier Boeing aircraft, such as the 707, 727 and 737 classics, the levers were roughly synchronized; however, the Next Generation has as a computer-operated fuel control system which can minutely adjust the %N1 of each engine.  This advanced fuel management can be observed in a real aircraft whereby each throttle lever creeps forward or aft independent of the other lever.

Programming flight simulator to read separate %N1 outputs for each engine, and then extrapolating the data to allow two motors to move the throttle levers independently is possible; however, the outputs are often inaccurate (for varying reasons).  This inaccuracy can often be observed on reproduction throttle units that exhibit a gap between lever one and lever two when automating %N1 outputs.  

It was decided to maintain the older system and have both levers synchronized.  Although this is not replicating the Next Generation system, it does make calibration easier.  If in the future incremental thrust lever movement is required, it’s a matter of adding another 12 Volt motor to the front of the throttle bulkhead to power the second thrust lever.  

Autothrottle activation will advance both thrust levers in unison to the fmc calculated %N1 output

Be aware that although both thrust levers are synchronized, the throttle handles may still show a slight difference in position in relation to each other.  This is caused by the varying tension that needs to be maintained on the fan belt connecting the 12 Volt motor to the mechanical system beneath the thrust levers.

Another aspect to note is that the position of the thrust levers during automation is arbitrary and is a visual representation of the %N1 output; it may or may not reflect the exact position on the throttle arc that the thrust lever would be placed if moved manually (by hand with Autothrottle turned off).  

Although the throttle is automated, manual override (moving the thrust levers by hand) is possible at any time, provided the override is within the constraints of the aircraft logic (programmed into the Alpha Quadrant card), and that provided by the flight avionics (ProSim737).  

Power Requirements and Mechanics

To provide the power to move the throttle thrust levers, a 12 Volt motor previously used to power electric automobile windows, is mounted forward of the throttle bulkhead (see image at bottom of post).  Connected to the motor's pulley is a fan belt that connects to the main pulley located beneath the thrust levers.  To enable the thrust levers to move in unison, a slip clutch, which is part of the main pulley assembly, is used.  

Captain-side TO/GA button is clearly seen below lever handles.  The button at the end of the handle is the Autothrottle disconnect button

ProSim737 Limitations - TO/GA and Auto Throttle Override

Unfortunately, concerning automation the ProSim737 is deficient in two areas: TO/GA and A/T Override.

(A)  TO/GA

In the real aircraft, the flight crew advances the thrust levers to power 40%N1 (or to whatever the airline policy dictates), allows the engines to spool, and then pushes the TO/GA button/s.  Pressing TO/GA causes the throttle to go on-line and to be controlled by the AFDS logic.  The throttle levers then advance automatically to whatever %N1 the logic deems appropriate based on takeoff calculations.

As at the time of writing. If you're using ProSim737, this will NOT occur.  Rather, you will observe the thrust levers retard before they advance (assuming you have moved the thrust levers to %40 N1).  The reason for this is nothing to do with how the throttle is calibrated, FSUIPC or anything else.  ProSim737 software controls the %N1 outputs for the automation of the thrust levers and the developer of the software has not fine-tuned the calibration in the software to take into account real-world avionics logic.  This thread located on the ProSim737 forum provides additional information. 

I have not tested Sim Avionics, but have been told this issue doesn't occur in their avionics suite.

There are two workarounds:  Engage TO/GA from idle (hardly realistic) or push the thrust levers to around 80% N1, allow the engines to spool, then push TO/GA.  Anything less that around 80% N1 will cause the thrust levers to retard before advancing.

Latest ProSim737 release (V133)

The latest version of ProSim737 (V-133) has provided improvement to the above issue.  Throttles can now be advanced to ~60% N1 and TOGA engaged without the throttle levers retarding.  This is possible ONLY if you calibrate the throttle levers within ProSim and allow ProSim to control the throttle output logic.  if you calibrate within FSUIPC then the same issue will apply.

According to ProSim developers, this issue is probably related to the calibration of the ProSim servo output. When you press TO/GA, the current N1 is taken and calculated back to a throttle percentage. This throttle percentage, when combined with the servo calibration data from ProSim results in a servo output. The servo calibration at the moment only has 2 calibration points, which are 0 and 100%. This results in a linear behavior between the two points, while depending on the construction of the throttle, the relationship might be non-linear. This would require a multi point calibration which is hard to do at the moment, because a throttle does not have exact readouts of the current position, so it will be hard to calibrate a 50% point.

This may need improvement in the code to auto calibrate the throttle system.

It's hoped that future release of ProSim737 will rectify this issue.

(B) Autothrottle Manual Override

In the real aircraft, manual override is available to a flight crew and the thrust levers can be retarded with the Autothrottle engaged.  When the flight crew release pressure on the thrust levers the Autothrottle will take control again and return the thrust levers to the appropriate position on the throttle arc dependent upon the speed indicated in the speed window of the MCP.

ProSim737 will not temporarily disconnect (manual override) the Autothrottle.  

At the time of writing, there is no workaround to solve this.

Potentiometers

There are many types of potentiometers; the two types most commonly used in flight simulation are the linear and rotary types. Linear potentiometers are inexpensive, often have a +- percentage variance, are compact, have a minimal throw depending upon the size of the device, and are not immune to contaminates building up on their carbon track. 

The last point is worth mentioning, as it is wrongly assumed that a potentiometer will remain correctly calibrated for the life of the unit.  General wear and tear, dust, and other debris will accumulate on the potentiometer; any of which may cause calibration and accuracy problems.  Keeping the potentiometers free of dust is important.

Rotary potentiometers (which may have a string attached) are very accurate, are in a sealed case and have very minimum chance of contamination. They are also made too exacting standards, are larger in size, and are expensive.

To read further about potentiometers

QAMP secured to base of throttle unit.  Thumb screws are visible on each corner of the plate.  A possible add on modification to reduce the risk of dust contamination to the potentiometers is a plastic cover that fits over the plate (a lunch box)

Calibration of Potentiometers

The main method of calibrating the position of the thrust levers is by calibrating the potentiometer in Windows, then in FSX followed by fine tuning in FSUIPC (if needed).  

At the moment I am using linear potentiometers; therefore, at some stage cleaning or replacement may be required.   The 737 throttle quadrant is not cavernous and only certain sized potentiometers will fit into the unit; this combined with other parts and wiring means that the potentiometers are often inaccessible without removing other components.  

To allow speedier access to the potentiometers, a Quick Assess Mounting Plate was designed.

quick access mounting plate (QAMP). four linear potentiometers are mounted to the plate. Two grub screws secure the plate to the throttle chassis

Quick Access Mounting Plate (QAMP)

The potentiometers are mounted directly onto a custom-made aluminum plate that is attached to the inside of the throttle unit by solid thumb screws.   To access the plate, the side inspection cover of the throttle is removed (a few screws) followed by turning the thumb screws on the access plate.  This releases the plate.

A similar plate has been designed and constructed for use with the stand-by potentiometer that controls the flaps.  A more detailed picture of the QAMP can be seen here..

Below is a video showing the movement of the thrust levers with the autothrottle engaged recorded during a test flight. 

 
 

Teething Issues with the Throttle Conversion

It was envisaged that more problems would have surfaced than have occurred.  The major issues are outlined below:

(A) Trim Wheels

An early problem encountered was that the trim wheels when engaging generated considerable noise.  After checking through the system, it was discovered that the two-speed rotation of the trim wheels were causing the two nuts that hold each of the trim wheels in place to become loose.  This in turn caused the trim wheels to wobble  slightly generating undue noise.  

Solution:

Tighten the two nuts at the end of the rod that holds the two trim wheels in place.

(B) Flaps 5 Not Engaging

The problem with the flaps 5 micro-button has been discussed in an earlier post.  To summarize, when you moved the flaps lever to flaps 5 the correct flaps were not selected on the aircraft or registered on the PoKeys 55 interface card.  Several hours were spent checking connections, micro-buttons, wiring and the custom VGA cables that connect the flaps section of the quadrant to the appropiate interface module; the problem could not be discovered.  

Solution:

One of the two Belkin powered hubs located within the IMM had been replaced with another powered unit.  It appears the problem was that the replacement hub had too low a voltage, as a replacement with a higher voltage solved the problem.

(C) Throttle Thrust Levers Not Synchronizing (A/T on)

The two thrust levers of the quadrant did not synchronize when the Auto Throttle (A/T) was engaged; one lever would always be ahead or behind of the other.  At other times they would split apart (do the splits) when A/T was engaged.  

Solution:

The problem was easily solved by altering the tension on the slip clutch nut.  When the nut was  tightened, both levers moved together as one unit.  The secret was finding the appropriate torque.

(D) Throttle Thrust Levers Difficult To Move in Manual Mode (A/T Off)

The ability to move the thrust levers in manual mode (Autothrottle turned off) was not fluid and the levers occasionally snagged or were sticky when trying to move them.  

The fan belt is barely visible linking the pulley of the motor to the main pulley inside the quadrant

This is caused by the fan belt not moving smoothly through the groove of the pulley wheel.   The Autothrottle when engaged overrides any stickiness due to the power and torque of the Auto Throttle motor.

Solution:

Unfortunately, there isn’t a lot you can do to rectify this issue as it’s a by-product of using a mechanical system in which the fan belt is central to the consistent operation of the unit.  

The conundrum is that if you tighten the fan belt too much you will be unable to manually move the thrust levers as they will be exceptionally stiff and difficult to move (as you are pushing against the tension of the fan belt); however, if you loosen the fan belt too much, although the levers will move fluidly by hand, the fan belt may not have enough tension to move the levers when Auto throttle is engaged.  It’s a matter of compromise; selecting an appropriate in-between tension to allow acceptable manual and Autothrottle operation.

A more reliable method is to use a small gearbox, a simple slip clutch and a coupler to connect to the spur gear.  Another option is to use an electrical system.

Further thought needs to be done in this area before a decision is made to replace the fan belt system.  If a new system is incorporated, the change-out will be documented in a future post.

Conclusion

Despite some of the shortcomings to this conversion, in particular the mechanical fan belt system, the throttle unit shows a marked improvement on the earlier 300 series conversion. 

Since the project began there has been three throttle conversions, and wth each conversion has built upon knowledge learnt from earlier conversions.  Initially there was the 737-300 conversion in 2012, which was converted in a rudimentary way and only operated in manual mode.  This was followed by the conversion of the 737-500 throttle in 2016.  This throttle was then rebuilt and upgraded in 2017.

Further Information

  • A summary of the articles that address the conversion of the 737-500 series throttle quadrant conversion, and the rebuild and update can be found in Flight Controls/Throttle Quadrant.

Acronyms and Glossary

  • AFDS - Autopilot Flight Director system

  • A/T – Autothrottle

  • CMD A/B - Autopilot on/off for system A or system B

  • Flight Avionics Software - Sim Avionics, ProSim737 or similar

  • FMC - Flight Management Computer

  • MCP - Main Control Panel

  • QAMP – Quick Access Mounting Plate

  • Throttle Arc – The arc of the thrust levers from the end of the blocks to fully forward.  The term refers to the curved piece of aluminum that the throttle levers are moved along

  • TO/GA - Takeoff Go-around switch

  • %N1 -  Very simply explained, %N1 is throttle demand and as N1 (and N2) spin at absurdly high speeds, it is easier to simply reference a percentage and display that to the crew. It's much easier for our brains to interpret a value on a scale of 0-100% rather than tens of thousands of RPM 

Adding A New Forward Section To The Existing Platform

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nicolson rotary router

After spending time working with some minor, but frustratingly time consuming 'teething problems' with the throttle quadrant, I decided it was time to do something different.  Therefore, I have added a meter or so to the front of the platform.  The reason for the addition was to make an area on the platform for the computers and power supplies to reside, rather than just sit on the floor of the room.

Addition From Wood - Not Aluminum

To use aluminium for the forward addition is a  waste of material and resources.  After all, the forward section of the platform is located behind the Main Instrument Panel (MIP) and is not readily visible.  I have used wood obtained from the local recycling center - I enjoy recycling products as much as possible... 

The platform I am using is modular, and it's comparatively easy to add sections to increase its overall size.

In the photograph above, a Nicolson router is being used  to make the circular holes that will be used to route the cables from the throttle quadrant to the Interface Master Module (IMM) and computer.   .

Nicolson Tools (USA)

Nicolson tools are made in the USA and the company produces very heavy and beefy products; the very sharp router made short work of the 2 cm thick wood

The forward platform addition will fit snugly against the existing aluminium platform and blend almost seamlessly.

Other articles dealing with the floor structure can be read below.

B737 Throttle Quadrant - Parking Brake Mechanism

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oem 737-500 parking brake lever and light

This post we will briefly discuss the conversion of the parking brake mechanism, and a video will demonstrate the solenoid engaging to move the lever within the mechanism.   The function of the parking brake is self-explanatory.

Parking Brake - Solenoid Auto Release

The parking brake can be engaged or disengaged by either engaging (lifting) or disengaging (pushing down) the park lever, or by depressing the toe brakes located on the rudder pedals. 

In the real aircraft, mechanical linkages and a cam disengage the parking brake.  A solenoid has been installed to replicate this in the simulator.

Interfacing with Flight Simulator

To use the solenoid, a relay card (on/off) and standard toggle-style switch is used.  The relay card is mounted in the Trial Interface Master Module (IMM) and connection from the throttle to the IMM is via a straight-through custom VGA cable. Any brand relay card will do this job.

Red Bulb

The red light is illuminated by a 28 Volt bayonet-style light bulb.  The bulb can be downgraded to 12 Volts; however, the illumination produced will not be as bright as if a 28 volt bulb was used. 

Spring, Solenoid and Toggle

The operation of the park brake lever revolves around four items:

  1. A long rod that connects from the lower section of the park lever to the toggle switch;

  2. A standard on/off toggle-style switch;

  3. A solenoid;

  4. A high tensile spring; and,

  5. A relay card.

parking brake Solenoid attached to port side firewall of throttle unit

When the park brake lever is pushed down or pulled up a corresponding movement of the long rod occurs.  Connected to the lower part of the rod is a standard-style toggle switch and a spring.  The spring is attached to the base of the throttle unit.  Movement of the rod causes the toggle to either be switched on or off (up/down), while the spring provides the tension for the automatic movement of the park lever to occur when the solenoid is energized (the lever is pulled downwards to the disengaged position).  A relay card is connected to the solenoid to control the timing that the solenoid receives power.

Toe Brakes Activation of Park Brake

As in the real aircraft, the parking brake can be released by the pilot depressing the toe brakes. 

There are  two methods commonly used to connect the toe brakes to the release of the park brake lever and parking brakes.  

The first (and easiest) method uses a Phidget 0/0/4 (1014_1) relay card and logic from within FSX or the avionics software (ProSim737), while the second method is a standalone closed system that can be implemented using a double-throw relay and a momentary switch; the switch being specific to the park brake.  For simplicity, I have incorporated the first method into the simulator as ProSim737 and FSX already provide a software solution to release the parking brakes.

Below is a short video showing how the parking brake mechanism operates.

 

737 throttle parking brake mechanism

 

In the next and final post regarding the throttle conversion, we will inspect the movement of the thrust levers during engagement of the Autothrottle (A/T) and discuss some of the teething issues with the throttle conversion.

Update

on 2017-06-26 06:40 by FLAPS 2 APPROACH

In June 2015, this mechanism was replaced with a more reliable system that replicates how the system operates in the real Boeing aircraft.  The system now in place is purely mechanical and does not rely on ProSim-AR for operation (other than registration of the movement of the parking brake lever).

B737 Throttle Quadrant - Trim Wheels and Trim Indicator Tabs

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Captain-side trim wheel and trim tab indicator.  I was fortunate that the throttle unit I aquired retained its light plates in excellent condition.  It's not uncommon to find that the light plates are faded, scratched and cracked from removal of the unit from the aircraft

This post, the third last concerning the throttle quadrant conversion, will discuss the spinning of the trim wheels and movement of the trim tab indicators; both integral components of the throttle quadrant.  For a list of articles about the conversion of the throttle quadrant, see the bottom of this page.

1:  TRIM WHEELS

The trim wheels were implemented by Boeing in the mid 1950’s with the introduction of the Boeing 707 aircraft and been a part of the flight deck ever since.  The main reason Boeing has continued the use of this system in contrast with other manufacturer, who have removed the spinning trim wheels is redundancy.  Boeing believes that the flight crew should have the ability to manually alter trim should a number of cascading failures occur.

Whatever the reason for Boeing continuing with this older style technology, many flight crews have learnt to “hate “ the spinning trim wheels.  They are noisy and distracting, not to mention dangerous if a flight crew accidentally leaves the handle in the extended position; there is a reason that they are called “knee knockers”.  

Many virtual pilots are accustomed to using manual trim when flying a Cessna or a small twin such as the King Air.  In such aircraft altering trim by hand is straightforward and a necessary part of trimming the aircraft.  However, a jet such as the B737 it is a tad different; to alter the trim by hand would require the flight crew to manually rotate the trim wheels several dozen times to notice any appreciable result in trim.  As such, the electric trim switches on the yokes are mainly used to alter trim.

Motors, Interface Cards and Speed of Trim Wheel

The power to spin the trim wheels comes from two 12 Volt DC pump motors installed within the throttle unit.  A Phidget High Current AC Controller card is used to interface the trim wheels to the flight avionics software (proSim737). The cards are located in the Interface Master Module (IMM) and connected to the throttle unit by customised VGA cables.

The trim wheels can spin at two speeds.  The autopilot producing a different speed to that of manual trim (no automation selected).  A Phidget card is used to control the variability, with each of the two channels programmed to a different speed.  To alter the actual revolutions of the trim wheel, each channel is accessible directly from within the ProSim737 software configuration.   

To allow the trim system to be used by CMD A and/or CMD B, a second card is installed to ensure duplicity.  

Correct Timing

The trim wheels have white longitudinal line painted on each trim wheel.  This line serves two purposes: as a visual reference when the trims wheels are spinning, and to determine the number of revolutions per second during calibration.  To ascertain the correct number of wheel revolutions per second, a digital tachometer is used in the same way a mechanic would tune an older style motor vehicle.

Out of interest, in manual trim, 250 revolutions of the trim wheels are necessary to move the trim tab indicators from full up to full down.

Two Speed or Four ?

The B737 has four different trim revolution speeds, each speed dependent upon the level of automation used and the radio altitude the aircraft is above the ground.

Although it is possible to program this logic into the Alpha Quadrant cards and bypass ProSim737 software entirely (closed system), it was decided not to as the difference in two of the four speeds is marginal and probably unnoticeable.  Further, the level of complexity increases somewhat programming four speeds. 

Autopilot mode rotates the trim wheels at a faster rate than when in manual trim.

Trim wheel removed showing heavy duty spline shaft

Trim Wheel Braking

The real 737 incorporates a braking mechanism on the trim wheels that inhibits wheel movement when there is no input received to the system from either the auto pilot or electric trim switches. The brake operates by electromagnetic radiation and is always on, being released when an input is received.  

An unsuccessful attempt was made to replicate this using two military specification high torque brake motors.   The motors incorporate a brake mechanism, but the torque was so high and the breaking potential so great, that when the brake was reengaging/disengaging there was a loud thud that could not be ignored.  Further, the motor became very hot when the brake system was engaged and vibrated excessively due to its high power rating.

At the time, a lower torque motor could not be procured and a decision was made to use the 12 volt pump motors.  Therefore; the trim wheels take an extra second or so to spin down – not a major imposition and barely noticeable when flying the aircraft..

Deactivating Trim Wheel Spinning

Most of my virtual flying is at night and noisy and vibrating trim wheels can easily aggravate others in the house attempting to sleep.  To allow easy disconnection of the trim wheels, I have configured the right side trim stabilizer toggle to cut the power to the trim wheels.  Although not authentic, sometimes minor alterations need to be made to a system to make it more user friendly.

2:  TRIM TAB INDICATOR MOVEMENT

The trim tab indicators are used as a visual reference to indicate to the flight crew the trim of the aircraft.  The trim and subsequent movement of the indicator tabs are activated either by depressing the electric trim switch on the yoke or by turning the trim wheels by hand.

Phidget Card

A Phidget Motor Controller Advanced Servo card and servo is used to control the movement of the two trim tab indicators, while the logic to activate the servo is directly from the flight avionics software.  The speed that the trim tabs move is set through ProSim737 (trim speed).

Aluminum tab connected to servo.  Servo is mounted behind aluminium plate.  You can just make out the screw wire between the servo and the tab

Hardware Modifications

To allow the servo to connect directly to the trim tab indicators, a small tab of aluminium was welded to the main trim tab shaft.  A thin screw wire was then connected from the servo to the tab to allow nay movement of the trim tab to be registered by the servo. 

Determining Accuracy

There is little point in implementing movement of the trim tab indicators if a high level of accuracy is not possible; therefore, it’s important that that the position of the tabs matches that of the flight avionics software and virtual aircraft.  To ensure positional accuracy and maintain repeatability the servo was calibrated throughout its range of movement and checked against the “virtual trim tab strip” that can be placed on the EICAS screen within the ProSim737 software.  

The short video below shows the smoothness in movement of the trim tab indicators.  You will note the TQ vibrates somewhat.  This is because I have yet to secure it to the platform.

 
 

B737 Throttle Quadrant - Flaps UP to 40; Conversion and Use

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This post examines the flaps lever on the refurbished B737 throttle and how it was converted to flight simulator use..

Flaps are used to slow the aircraft by creating drag, and to apply positive lift during takeoff.  The flaps lever is located on the First Officer’s side of the throttle quadrant. 

Subsequent movement of the flaps lever is indicated by illumination of the Le Flaps Transit and Le Flaps EXT lights located on the Main Instrument Panel (MIP), movement of a needle in the flaps gauge, a change of indication in the Primary Flight Display (PFD) and illumination of the Leading Edge Device (LED) panel located on the aft overhead panel. 

There are other less obvious indicators, but this is not the direction of his post.

The flaps lever is an integral part of the throttle unit.  Ensuring it operates correctly and with accuracy is important.

oem 737 throttle showing flaps arc and takeoff cg%mac

Safety Features

Newcomers to an OEM throttle quadrant are often surprised at how difficult it is to manipulate the flaps lever; it isn't a simple pull or push of a lever - there is a reason for this. 

When flaps are extended, especially at slow air speeds the flight dynamics of the aircraft are altered.  To protect against accidental flap extension, Boeing has designed the flaps lever so that a flight crew has to physically lift the lever before moving the lever to the required flap setting.  

Further safety has been designed into the system by having flaps 1 and flaps 15 guarded by a flaps gate.  The gate prevents straight-through movement of the flaps lever beyond flaps 1 and 15.  The  pilot must actually lift, push and drag the lever through the gate to the next setting.

It takes a short time to become accustomed to how to move the lever for smooth operation.

Traditional Approach used in Flaps Conversion

In most throttle conversions, a single potentiometer is used and the flaps are calibrated directly through FSUPIC.  A linear rod is attached to the potentiometer and then to the lower end of the flaps lever.  When the flaps lever is moved, the rod is moved forward or aft causing the potentiometer to turn to a defined and pre-calibrated position.  The analogue movement of the rod is converted to a digital signal that can be read by Flight Simulator.

In such a conversion, it’s important to ensure that the physical position of the flaps lever matches the flaps position used in Flight Simulator and in the flaps gauge.  It’s also vital that flaps are calibrated to ensure accurate operation.

The benefits of using this traditional method are that it’s “tried and true”, inexpensive and relatively easy to implement.  Calibration is the major key; however, using FSUIPC can be troublesome and time consuming, although once calibrated everything should operate reasonably well.  

Potentiometers - Accuracy and Longevity

Potentiometers came in a variety of sizes with differing throw values.  A throw is the length of movement that a potentiometer will allow a linear rod to move.  The larger the potentiometer the more throw allowed.  The potentiometer for the flaps must fit within the throttle unit beneath the flaps mechanism in a relatively small space.  Unfortunately, with Boeing 737 late model throttle’s there is minimal room to allow a larger than 60mm potentiometer to be installed.  Using a 60 mm potentiometer means that the device has a minimal throw.

This throw, if lucky, can be stretched to cater from flaps 0 to flaps 40, but only after facetiously calibrating with FSUPIC.  More often than not,  the throw will only reach flaps 1 or flaps 30.  Often this lack of throw goes unnoticed and many virtual pilots select flaps 40 believing they actually have flaps 40, but in reality it is flaps 30.

Longevity is another more minor issue when using potentiometers.  Most potentiometers have a +- tolerance during manufacture, are made cheaply and depending upon the type selected are open to contamination from dust and debris.  Dust on a potentimeter can affect the accurancy of the unit. At the very least, maintenance is required if the potentiometer is located in a dusty area.

Several Ways to Skin a Cat.....

To solve these potential problems two methods were assessed.  The first was using two micro- buttons at each end of the linear rod that connects the flaps lever with the potentiometer.  These buttons can be assigned directly with FSUPIC to flaps UP and flaps 40.  This theoretically would solve the shortness of throw experienced with traditional conversion and calibration.  Flaps UP and 40 are controlled by micro-buttons and everything in-between is calibrated within FSUPIC.

Working through an issue with the Flaps 5 micro button, custom VGA cable and PoKey card. it's not all fun.  Chasing problems can be frustrating and very time consuming

Micro-buttons

The second method is to replace the potentiometer with micro-buttons; thereby,  rectifying the issue of minimal throw.  Replacement will also alleviate the chance of a potentiometer being inaccurate, remove any chance of contamination, and also remove the tedious task of calibrating flaps in FSUIPC.   

The use of micro-buttons to control flaps movement is relatively novel, but the potential benefits of implementing this into the throttle unit could not be overlooked; therefore, it was decided to use this method.

Problems with Micro-buttons - Design of Lower Flaps Arc Plate (LFAP)

The first initial problem encountered is that micro-buttons are small, delicate and can be easily damaged if mounted directly onto the metal flaps arc.  Manipulating the flaps lever requires considerable pressure to pull, drag and drop the lever into the correct flaps detent position. Clearly, mounting the buttons on top of the metal flaps arc for direct contact with the flaps lever was not feasible.

After much thought, it was decided to fabricate from aluminum, a plate that replicated the arc that the flaps lever moves over.  This plate has been called the Lower Flaps Arc Plate (LFAP).  The micro-buttons were then strategically mounted to the plate, each buttons’ position corresponding to a flap position.  The LFAP with the mounted buttons was then mounted directly beneath the existing flap arc plate. 

Design Considerations

Before implementing a new design, considerable thought must be taken to potential problems that may arise from the design.  In the case of using micro-buttons the issue was connectivity and the possibility of a damaged or faulty button.  The LFAP can be accessed relatively easily by removing the First Officer's side panel which allows access to the plate from behind the trim wheel.

Half-moon Provides Accuracy, Reliability and Repeatability

To enable the micro-buttons to be triggered by the flaps lever, a half-moon piece of aluminum was fabricated using the same dimensions of the lower portion of the flaps lever.  One end of the "half-moon" was  curve-shaped pointing downwards. The "half-moon" was then screwed to the lower section of the flaps lever handle   

LEFT:  Rough initial sketch of half-moon showing relationship to flaps arc and micro-buttons.

When the flaps lever is dropped into a flaps detent position, the curved side touches and depresses the micro-button mounted on the lower flaps arc plate.  When the flaps lever is moved to another flaps setting, the lever is first lifted breaking contact with the button, moved to the next setting and dropped into the detent position triggering the next button and so forth.

Interface Card

A standard PoKeys 55 interface card was used to connect the outputs from the buttons to the avionics suite software.  ProSim737 software allows easy interfacing by allowing direct connection of a button to a specific flap position.  If ProSim737 is not used and the chosen avionics suite does not support direct connection, FSUIPC can be used to assign individual buttons to flap positions.  The PoKeys card is installed in the Interface Master Module (IMM).

Advantages of Micro-buttons - It's Worth The Effort...

The benefits of using micro-buttons cannot be underestimated. 

  • 100 % accuracy of flap movement from flaps UP to flaps 40 at all times.

  • No calibration required using FSUIPC.

  • Non-reliance on FSUIPC software as the installation is mechanical.

  • Very easy configuration of flaps UP through flaps 40 using ProSim737 software configuration.

  • Removal of the potentiometer and possible inaccuracy caused by +- variation.

  • No concern regarding possible contamination of the potentiometers.

  • Enhanced reliability of operation with no maintenance required.

  • Easy removal of the Lower Flaps Arc Plate to facilitate button replacement.

Back-up Potentiometer System

Although the use of micro-buttons is successful, I still have a potentiometer installed that can be used to operate the flaps.  The reason for installing the potentiometer was in case the micro-buttons did not work correctly; it would save time installing a replacement system.  To change from buttons to the potentiometer is as easy as disconnecting one quick release connector and reconnecting it to another.

qamp. the quick access mounting plate enablse 4 linear potentiometers to be mounted in one location. the qamp is located in throttle unit

Quick Access Mounting Plate (QAMP)

The potentiometer is mounted directly onto a custom-made aluminum plate that is attached to the inside of the throttle unit by solid thumb screws. 

The reason for the plate and screws was easy access should the potentiometer need to be cleaned or be replaced. 

To access the potentiometer requires the side inspection plate of the throttle be removed (a few screws) and then removal of the thumb screws on the access plate that allows the potentiometer to be dropped from its bracket.

Unfortunately, I failed to photograph the flaps QRMP before installation; however, its design is similar to all quick release plates used within the throttle unit.  The plates are made from aluminium and are attached to the throttle unit by thumb screws rather than nuts and bolts.  This allows for easier and faster change out if necessary.  The above image shows the QRMP for the throttle levers - the flaps QRMP is far smaller and thinner.

Troubleshooting

During testing a problem was observed with the micro-button for flaps 5.  For an unknown reason flaps 5 would not register correctly on the PoKeys 55 card.  After several hours troubleshooting the buttons and wiring, it was determined that the PoKeys card must have a damaged circuit or connection where they flaps 5 wire was installed to the card.

The problem turned out not to be the PoKeys card, but the Belkin USB hub installed to the Interface Master Module (IMM).  I had replaced the first hub (which I damaged) with another hub that had a lower voltage.  For some reason this lower voltage was not enough to allow operation of all the functions running from the hub. 

After replacing the hub with a higher voltage device, the issue with the flaps was immediately rectified.  Of course, this was after I spent literally hours troubleshooting flaps 5!  As stated earlier, teething issues on a new design can be frustratingly time consuming...

Video

I decided to make a short video that explains the button set-up a little better.  In the video you can clearly see the flaps arc, half-moon pencil and the micro-buttons.  The video is not the best quality as it was hand held in dim light after I removed the F/O side inspection plate of the throttle quadrant.  It's difficult if not impossible to setup a tripod in the flight deck once the throttle unit is bolted to the platform.

 

737 throttle flap arc buttons

 

Acronyms and Glossary

  • Flaps Arc – A curved piece of aluminum positioned directly beneath the flaps lever and corresponds to the curvature of the light plate.

  • Lower Flaps Arc Plate (LFAP) - A curved piece of aluminium that is the same size as the flaps arc and is mounted directly beneath the flaps arc.

  • Half-Moon Pencil – a custom fabricated piece of aluminum with a curved edge at one end.  Used to depress micro-buttons on flaps arc as flaps lever is moved..

  • OEM - Original Equipment Manufacturer.

  • Quick Access Mounting Plate QAMP – Quick Access Mounting Plate for the potentiometer that is a redundancy system for flaps movement.

  • Avionics Suite - Software that interacts with Flight Simulator to control avionics, gauges, etc - ProSim737, Sim Avionics, Project Magenta, etc.

Update

on 2014-02-12 02:13 by FLAPS 2 APPROACH

flaps half-moon

Several individuals have contacted me asking for a picture of the half moon, that is roughly sketched in the main post.  During a recent upgrade, the side panel and trim wheel were removed so I took the opportunity to take a photograph of the half-moon.

The half moon is secured to the lower section of the flaps lever by a screw, with the lower curved side facing downwards towards where the micro-buttons are positioned. The half-moon moves in unison with the flaps lever (when moved) and the curved section triggers micro-buttons as it passes over the button.  The micro-buttons are positioned at the correct position that relate to a specific flap detente.

Update

on 2019-09-09 07:29 by FLAPS 2 APPROACH

FLAPS OVERHAUL (LATE 2018/2019)

The mechanism used to convert the flaps on the throttle quadrant has been overhauled and replaced.  The method described in the above article worked well, however, a number of problems developed that were only noticeable after continual use.