Flow Sequence To Enter Information To Flight Management Computer (FMC)

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OEM 737-500 CL CDU

Specific information must be entered into the Control Display Unit (CDU) if the Flight Management Computer (FMC) and Flight Management System (FMS) is to function correctly. To ensure that all the appropriate data is entered, a flow sequence is usually used by a flight crew to enter data into the CDU.

Each aircraft is normally equipped with two Control Display Units; one on the Captain-side and one the First Officer-side.  Each CDU can be used either in tandem or independently of each other. 

In this article, I will discuss the preferred flow sequence that should be used to enter information into the CDU pre-flight.  It should be noted that, like many aspects of aviation there are usually several ways to achieve a similar if not identical result.  Often airline policy will dictate the sequence that the CDU is configured, and by which pilot.  Therefore, the below information should be treated as a guideline rather than an inflexible set of rules. 

The information used comes in part from the aircraft’s flight plan and load sheet.

  • The content of this article has been reviewed by a Boeing 737 Captain for accuracy.

FMC Software

The Flight Management System (FMS) is controlled by software and the software version used is often dependent on the age of the aircraft; not all software is identical.   The information in this article refers to Software Version U10.8A.  U10.8A is the version used by ProSim737 (other simulation avionics suites may differ).  An earlier article discusses software variants.

Which Pilot Does What And When Is It Done

It is not uncommon for the pilot’s to share the task of setting up the CDU.  Usually the pilot flying (PF) will enter parameters that are essential to flight, while the pilot not flying/monitoring (PM) will enter information pursuant to the route.

However, the hierarchy in a flight deck is that the Captain is the Pilot In Command (PIC), and it is assumed that the First Officer will complete most of the mundane, albeit important, navigation tasks leaving the Captain to deal with other matters.

CDU Verification and Cross Checking Procedure

The CDU is nothing more than a ‘glorified keypad’ and the maxim of ‘rubbish in rubbish out’ applies.  Until execution (pressing the illuminated execute button on the keypad), none of the information entered into the CDU will be reflected in the FMC and FMS.   Therefore, it is important that prior to execution, each pilot review and confirms the other’s inputs.  Cross checking and verification minimises the chance that incorrect information has been entered.  

At a minimum, a flight crew should compare the filed flight plan with the airways and waypoints entered on the ROUTE pages.  The flight plan total distance and estimated fuel remaining at the destination should also be reviewed on the progress page of the CDU.  If a discrepancy is noted, the LEGS page must be updated to ensure it is identical to the airways and waypoints in the filed flight plan.  A cross check using the Navigation Display in PLAN mode and the CDU in STEP function (LEGS page) will aid is verification of the flight plan and in determining if there are any discontinuities that need to closed.

Taxi and Flight

Before taxi, the Captain or First Officer may make CDU entries.  However, when possible, CDU entries should be made prior to taxi or when stopped.  If CDU entries must be made during taxi, the pilot monitoring makes the entries and the pilot flying concentrates on steering the aircraft. 

In flight, the pilot monitoring usually makes the CDU entries, however, the pilot flying may make simple CDU entries, but only when the workload allows.  Essentially, the pilot flying concentrates on flying the aircraft and if they wish to enter data to the CDU, then the responsibly of flying the aircraft should be transferred to the First Officer.

The pilot flying is responsible for setting up the approach page in the CDU.  To do this, the pilot flying will transfer command of the aircraft to the pilot not flying, and then make any amendments to  the approach in the CDU.  Upon completion, the command of the aircraft will be transferred and the pilot not flying will check the information.

Which Page in the CDU is Opened During Takeoff

The pilot flying usually will have the takeoff reference page displayed to enable the crew to have immediate access to V-speeds.  This is to counter against the rare event that the V-speeds are inadvertently removed from the airspeed display on the Primary Flight Display (PFD) due to a display failure.  Alternatively, the pilot flying may also elect (following the takeoff briefing in the Before Takeoff Procedure) to display the CLB page for takeoff.  

The pilot monitoring normally displays the LEGS page during takeoff and departure to allow timely route modification if necessary.

CDU Sequence Flow

There are numerous ways to flow from one CDU function to another.  The two commonly used methods are to use the Alpha Keys or the Line Select Keys (i.e. LSKL6).  For example, LSKL6 refers to line select key left 6 or the sixth lower button on the left hand side.

As stated, the pilot flying will enter any information relevant to the takeoff of the aircraft, while the pilot not flying will enter information pertaining to the route of the aircraft (i.e. route, legs).  

  • Bold CAPITALletters indicate that the command is an ALPHA menu key. 

PILOT NOT FLYING (PM)

  1. INIT REF / INDEX (LSKL6).

  2. POS (LSL2) – Enter airport identifier into Ref Airport.

  3. RTE or ROUTE (LSKR6) - Enter airport identifier (origin and destination), flight number (Flt No) and runway.

  4. DEP ARR – Enter departure information (DEP LSKL1) - SID and runway.

  5. LEGS– Enter airways, waypoints and navaids as required to a build a navigation route. 

  6. DEP ARR – Enter arrival information (ARR LSKL2) - STAR, approach, transition and runway. 

  7. On the EFIS, select PLAN and using the STEP function (LEGS Page) or PREV-NEXTPage, cycle through the waypoints checking the route on the Navigation Display.  Check the route and close any route discontinuities.  Return EFIS to MAP.

  8. ACTIVATE (LSKL6) / EXECor RTE / ACTIVATE (LSKR6) / EXEC.

PILOT FLYING (PF)

  1. INIT REF – Enter Zero Fuel Weight (ZFW), Fuel Reserves, Cost Index, Cruise Altitude (Crz Alt), Cruise Wind (Crz Wind), ISA Deviation (ISA Dev), Outside Air Temperature (T/C OAT) and Transition Altitude (Trans Alt).

  2. N1 LIMIT (or LSKR6) – Enter Derates as desired.

  3. LEGS / RTE DATA (LSKR6) – Enter wind (this determines fuel quantity on progress page).  Note #1.

  4. INIT REF / displays TAKEOFF REF page – Enter Flaps setting for departure and Centre of Gravity (Flaps and Trim).  Go to page 2/2 and input data to various fields as and if required.

  5. EXEC– Press illuminated execute key (this triggers the V-Speeds to be displayed on the TAKEOFF REF page).

  6. To select V-Speeds, press Line Select keys beside each V-Speed to activate (LSR1, 2 & 3). Note #2.

Notes:

  • NOTE #1:  Wind direction and speed (point 3) can be addedprior to or after the EXEC button has been selected.  The flow sequence will alter dependent upon when this information is added.  If the winds are not added, the flow will alter and TAKEOFF (LSKR6) will be selected instead of INIT REF.

  • NOTE #2:  If V-Speeds on the Takeoff page are not displayed, it is because either the EXEC key has been pressed prior to the Takeoff Page being opened and data entered.  If this occurs, cycle the QRH (LSKR6) on and off.  The V-Speeds will then be displayed.  Another reason that the V-Speeds may not be displayed is failure to input other essential pre-flight information. 

There is often confusion to what the QRH designation means.  When QRH is not selected (turned off) the V-Speeds will be automatically promulgated.  If QRH is selected (turned on) the V-Speeds will be shown in green beside the appropriate line.  This enables the flight crew to change the V-Speeds prior to executing them (note that ProSim-AR enables this to be altered in the IOS/Settings).

Additional Information

I usually do not link to outside resources, however, this U-Tube video from Mentour Pilot demonstrates the procedure quite well.  Scroll to 0:31 seconds to begin video.

 
 

For those interested in reading more about how the CDU, FMC and FMS and how they interrelate concerning information input, Randy Walter from Smiths Industries has put together a very good article called Flight Management Systems. 

Final Call

The CDU is an essential item that must be configured correctly if the aircraft’s internal navigation database is to be used.  Likewise, LNAV or VNAV will only operate if the information has been entered into the CDU correctly.

The sequence you enter the information into the CDU is important, and although some latitude to the flow is accepted, a correct sequence flow will ensure all essential variables are inputted.   Finally, cross verification of data, or any change to the data, ensures correct and accurate information is being entered.

Acronyms and Glossary

  • ALPHA Menu Key - Refers to the menu function keys.

  • CDU - Control Display Unit (the keypad).

  • FMC - Flight Management Computer.

  • FMS - Flight Management System.

  • LSK - Line Select Key.  Used to enter lower level pages.

  • QRH - Quick Reference Handbook.

OEM Trip Reminder Indicator

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Trip Reminder Indicator.  A small OEM part that is easily installed to any simulator

The trip reminder indicator (TRI) is a mechanical device installed to the right hand side of the yoke; it’s an airline option.  Basically, the device is three separate digits that can be rotated in any combination, from zero to nine.

The trip indicator is a memory device from which the crew historically used to record the flight number; the pilot uses his thumb to move the three digits to indicate the flight number.  However, over time flight numbers became longer than three digits and the use of the trip indicator, for it’s intended purpose, wanned

I use the trip indicator to dial in the Vref, as it’s often easier to quickly glance at the trip indicator to remind you of the Vref speed rather than look at the PFD or CDU.  Some dial in the Vref + wind speed.

Background

The trip indicator has a very long lineage beginning with the Boeing 707 aircraft.  The device was then ported to the 717, 727 and finally the 737 Classic and Next Generation airframes.

Installation and Backlighting

Because the OEM yoke already has the correctly shaped hole, installation of the trip indicator is straightforward.  If you are using an OEM yoke, you probably will need to carefully remove the blanking cover from the hole.

If a reproduction yoke is used, and the hole is not present, a circular hole will need to be cut from aluminium or plastic to enable the trip indicator to fit snugly into the yoke.  As the three dials are mechanical, there is no requirement to connect the device to an interface card.

Each of the digits on the indicator is backlit by a 5 volt incandescent aircraft bulb. 

The design of the trip indicator is ingenious, in that after the trip indicator has been removed from the yoke (two screws at the front of the yoke secure the indicator), a transparent acrylic slide can be unlocked to slide laterally from behind the three digits (see picture).  The acrylic slide accommodates three 5 volt bulbs, each in its own compartment.

To enable the backlighting to function requires two wires (positive & negative/common) to be connected to the appropriate connection on the rear of the trip indicator, and then to a 5 volt power supply.  The amperage draw from the three bulbs is minimal.  The wiring should be run through the yoke and down the control column so that it comes out at the bottom of the column.

In the aircraft, the backlighting for the trip indicator is connected to the panel light knob located on the center pedestal.  This enables the backlighting on the trip indicator to be turned on and off or dimmed. 

Final Call

The trip reminder indicator is but a small and unobtrusive item, however, it’s often the small things which add considerable immersion and enjoyment when using the simulator.  The trip indicator is also an OEM part that can be very easily installed to a reproduction yoke with minimal experience in fabrication and wiring.

Glossary

OEM - Original Equipment Manufacture.

Throttle Quadrant Rebuild - Flaps Lever Uses String Potentiometer

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Flaps lever set to Flaps 30.  The throttle quadrant is from a Boeing 737-500 airframe. The flaps lever arc is the curved piece of aluminium that has has cut-out notches that reflect the various flap positions.  It was beneath this arc that micro-buttons had been installed

There are several ways to enable the flaps lever to register a particular flaps détente when the flaps lever is moved to that position on the flaps arc.

In the earlier conversion, the way I had chosen worked reasonably well.  However, with constant use several inherent problems began to develop.

In this article, we'll examine the new system.  But before going further, I'll briefly explain the method that was previously used.

Overview of Previously Used System

In the earlier conversion, nine (9) micro-buttons were used to register the positions of the flaps lever when it was moved (Flaps UP to Flaps 40). 

The micro-buttons were attached to a half moon shaped piece of fabricated aluminium.  This was mounted beneath the flaps lever arc and attached to the quadrant.  Each micro-button was then connected to an input on a PoKeys 55 interface card.  Each input corresponded to an output.

Calibration was straightforward as each micro-button corresponded to a specific flaps position.

Problems

The system operated reasonably well, however, there were some problems which proved the system to be unreliable.  Namely:

(i)    The vertical and lateral movement of the chain located in the OEM throttle quadrant interferred with the micro-buttons when the trim was engaged; and,

(ii)  The unreliability of the PoKeys 55 interface card to maintain an accurate connection with the micro-buttons.

Movement of OEM Chain

The chain, which is similar in appearance to a heavy duty bicycle chain, connects between two of the main cogs in the throttle quadrant.  When the aircraft is trimmed and the trim wheels rotate, the chain revolves around the cogs.  When the chain rotates there is considerable vertical and some lateral movement of the chain, and it was this movement that caused three micro-buttons to be damaged; the chain rubbed across the bottom section of the micro-buttons, and with time the affected buttons became unresponsive.

First Officer side of a disassembled throttle quadrant  (prior to cleaning and conversion).  The large notched cog is easily seen and it's around this cog that the OEM chain rotates (the chain has been removed)

It took some time to notice this problem, as the chain only rotates when the trim buttons are used, and the micro-buttons affected were primarily those that corresponded to Flaps 5, 10 and 15.  The chain would only rub the three micro-buttons in question when the flap lever was being set to Flaps 5, 10 or 15 and only when the trim was simultaneously engaged.

The cog and chain resides immediately beneath the flaps arc (removed, but is attached to where you can see the four screws in the picture). 

Although there appears to be quite a bit of head- space between the cog and the position where the flaps arc is fitted, the space available is minimal.  Micro-buttons are small, but the structure that the button sits is larger, and it was this structure that was damaged by the movement of the chain (click to enlarge).

An obvious solution to this problem would be to move the chain slightly off center by creating an offset, or to fabricate a protective sleeve to protect the micro-buttons from the movement of the chain.     However, the design became complicated and a simpler solution was sought.

Replacement System

Important criteria when designing a new system is: accuracy, ease of installation, calibration, and maintenance.  Another important criteria is to use the KIS system.  KIS is an acronym used in the Australian military meaning Keep It Simple.

The upgraded system has improved reliability and has made several features used in the earlier system redundant.  These features, such as the QAMP (Quick Access Mounting Plate) in which linear potentiometers were installed, have been removed.

String Potentiometer Replaces Micro-buttons

Single-string potentiometer enables accurate calibration of flaps UP to flaps 40.  The potentiometer is mounted on a customised bracket screwed to the First Officer side of the throttle quadrant superstructure.  The terminal block in the image is part of the stab trim wheel system

A Bourne single-string potentiometer replaced the micro-buttons and previously used linear potentiometers.  The string potentiometer is mounted to a custom-designed bracket on the First Officer side of the throttle quadrant.  The bracket has been fabricated from heavy duty plastic.

A string potentiometer was selected ahead of a linear potentiometer because the former is not limited in throw; all the flap détentes can be registered from flaps UP through to flaps 40.  This is not usually possible with a linear potentiometer because the throw of the potentiometer is not large enough to cater to the full movement of the flaps lever along the arc.

A 'string' is also very sensitive to movement, and any movement of the string (in or out) can be accurately registered.

Another advantage, is that it's not overly important where the potentiometer is mounted, as the string can move across a wide arc, whereas a linear potentiometer requires a straight direction of pull-travel.

Finally, the string potentiometer is a closed unit.  This factor is important as calibration issues often result from dust and grime settling on the potentiometer.  A closed unit for the most part is maintenance free.

The end of the potentiometer string is attached to the lower section of the flaps lever.  As the flaps lever moves along the arc, the string moves in and out of the potentiometer. 

The ProSim737 software has the capability to calibrate the various flap détentes.  Therefore, calibration using FSUIPC is not required.  However, if ProSim737 is not used, then FSUIPC will be needed to calibrate the flap détente positions.

Advantages

Apart from the ease of calibration, increased accuracy, and repeatability that using a string potentiometer brings, two other advantages in using the new system is not having to use a Pokeys 55 card or micro-buttons.

Unreliability of PoKeys 55 Interface Card

The PoKeys card, for whatever reason, wasn't reliable in the previous system.  There were the odd USB disconnects and the card was unable to maintain (with accuracy and repeatability) the position set by the micro-buttons.

I initially replaced the PoKeys card, believing the card to be damaged, however, the replacement card behaved in a similar manner.  Reading the Internet I learned that several other people, who also use ProSim737 as their avionics suite, have had similar problems.

Micro-buttons can and do fail, and replacing one or more micro-buttons beneath the flaps arc is a time-consuming process.  This is because the upper section of the throttle quadrant must be completely dismantled and the trim wheels removed to enable access to the flaps arc.

Registering the Movement of the Flaps Lever in Windows

The movement of the flaps lever, prior to calibration must be registered by the Windows Operating System.  This was done using a Leo Bodnar 086-A Joystick interface card.  This card is mounted in the Throttle Interface Module (TIM).    The joystick card, in addition to the flaps lever, also registers several other button and lever movements on the throttle quadrant.  

Final Call

The rebuild has enabled a more reliable and robust system to be installed that has rectified the shortfalls experienced in the earlier system.  The new system works flawlessly.

  • This article displays links to the majot journal posts concerning the 737 throttle: OEM Throttle Quadrant. 

Acronyms and Glossary

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

Repair Backlighting on Throttle Quadrant

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The rear of the First Officer side trim lightplate showing one of the two terminals that the wiring loom connects to

During a recent flight, I noticed that the bulbs that illuminate the backlighting for the trim and flaps lightplate (First Officer side) had failed, however, the backlighting on the Captain-side trim lightplate was illuminated.  My first thought was that the 5 volt bulbs that are integrated into the lightplate had burned out; after all, everything has an end life.

Backlighting - Wiring Loom

The wiring loom that supplies the power for the backlighting enters the throttle quadrant via the front firewall, and initially connects with the trim lightplate and parking brake release light on the Captain-side.  A Y-junction bifurcates the wire loom from the Captain-side to the First Officer side of the quadrant, before it snakes its way along the inside edge of the quadrant firewall to connect with the First Officer side trim lightplate, and then the flaps lightplate.  The wiring loom is attached securely to the inside edge of the throttle casing by screwed cable clamps.

The backlighting for all lightplates is powered by 5 volts and the backlighting on the throttle quadrant is turned on/off/dimmed by the pedestal lighting dimmer knob located on the center pedestal. 

Finding the Problem

Ascertaining whether the bulbs are burned out is uncomplicated, however, assessing the terminals on the rear of each lightplate, and the wiring loom the connects to the lightplates, does involve dismantling part of the throttle quadrant.

The upper section of the throttle quadrant must be dismantled (trim wheels, upper and side panels, and the saw tooth flaps arc).  This enables the inside of throttle quadrant to be inspected more easily with the aid of a torch (lamp/flashlight).  When removing the trim wheels, be especially vigilant not to accidently pull the spline shaft from its mount, as doing so will cause several cogs to fall out of position causing the trim mechanism to be inoperable.

After the lightplates have been removed, but still connected to the wiring loom, a multimeter is used to read the voltage of each respective terminal on the lightplate. If the mutlimeter indicates there is power to the terminals, then the bulbs should illuminate. 

What surprised me when this was done, was that the bulbs worked perfectly. Therefore, it was clear the problem was not bulb, but wire related.

Process of Elimination

The process of elimination is the easiest method to solve problems that may develop in complicated systems.  By reducing the components to their simplest form, a solution can readily be attained.

Alligator wire connects power from Captain-side lightplate to the First Officer lightplate.  Note the frayed outer layer of the white aircraft wire.  The gold colour is a thin layer of gold that acts as a fire retardant should the wiring overheat

If you suspect that the wiring is the problem, and don't have a multi meter, then a quick and fool safe method is to connect an alligator cable from the positive terminal of the Captain-side lightplate to the respective terminal on the First Officer lightplate.  Doing this removes that portion of the wiring harness from the circuit. 

In this scenario, the  bulbs illuminated on both trim lightplates.  As such, the problem was not bulb related, but was associated with the wiring loom.

It must be remembered that the wire used to connect the backlighting in the throttle quadrant is OEM wire.  As such, the age of the wire is the same age as the throttle quadrant.  

Inspecting the wire loom, I noticed that one of the wires that connected to the terminal of the lightplate was severed (cut in two).   I also noted that the original aircraft wires had begun to shed their protective insulation layer. 

Aircraft Wire and Insulation Layers

The high voltage and amperages that travel through aircraft wire can generate considerable heat.  This is why aircraft wire is made to very exacting standards and incorporates several layers of insulation that surround the stranded stainless steel wire.  The use of high-grade stainless steel also provides good strength and resistance to corrosion and oxidation at elevated temperatures.  

The green wire has been severed.  A possible scenario was that the wiring loom had been pulled slightly loose from the throttle chassis, and had become caught in the flaps mechanism.  When the flaps lever is moved, the mechanism can easily crimp (and eventually sever) any wire in its path.  If you observe the white wire you can see the insulation that is shedding

Interestingly, one of the insulating layers is comprised of gold (Au).  The gold acts as an effective fire retardant should the wires overheat.

The breakdown of the upper insulating layer is not a major cause for concern, as a 'shedding' wire still has enough insulation to not arc or short circuit.  However, the wire should be replaced if more than one layer is compromised, or the stainless threads of the wire are visible.

Possible Scenario

When inspecting the wiring loom, I noted that one of the screws that holds the cable clamp to the inside of the throttle casing was loose.  This resulted in part of the wire loom to 'hang' near the flaps arc mechanism.    It is possible that during the throttle’s operational use, the movement and vibration of the aircraft had caused the screw to become loose resulting in the wires hanging down further than normal.  It appears that the wire had been severed, because it became caught in the mechanism of the flaps lever.  

Unlike reproduction throttles, the parts used in an OEM throttle are heavy duty and very solid; they are designed to withstand considerable abuse.  The speedbrake lever, when activated can easily cut a pencil in two, and the repeated movement of the flaps lever, when moved quickly between the teeth of the flaps arc, can easily crimp or flatten a wire.

Rather than try to solder the wires together (soldering stainless wire is difficult) and possibly have the same issue re-occur, I routed the wires from both lightplates (trim and flaps) directly to the 5 volt bus bar located in the center pedestal. 

I could have removed the wire loom completely and replaced it with another loom, however, this would involve having to disassemble the complete upper structure of the throttle quadrant to access the wire loom attachment points on the inside of the throttle casing; something I was not keen to do.

Final Call

OEM parts, although used in a static and simulated environment can have drawbacks.  Apart from age, the repeated movement of mechanical parts and the vibration of the spinning trim wheels, can loosen screws and nuts that otherwise should be securely tightened. 

Acronyms

  • OEM – Original Equipment Manufacturer

  • Wire Loom – Several wires bundled together and attached to a fixed point by some type of clamp

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.

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).

Assembly of Forward Overhead Panel

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Forward overhead using OEM parts

Construction of the simulator began in 2011.  It is now 2016 and I am perplexed to why the build has taken so long to complete.   Of course, opting to try and use OEM (Original Equipment Manufacture) parts whenever possible has added significant time to the project - especially the procurement of parts.

Most of the parts that make up the forward overhead have now been obtained and assembly of the components is well advanced.   Very soon the wiring from the panels to the Phidgets cards will begin.  This will be followed by several hours of testing to check correct functionality and to ensure perfect harmony between components and systems. 

A basic frame has been constructed to enable the overhead to be easily positioned to enable the wiring to be done with a little more ease.  After the forward overhead is completed, work on the aft overhead will commence.  Rome, it seems, was not built in a day.

Certainly, completion of the forward overhead will be the major project over the next few months.

Throttle Quadrant Rebuild - Parking Brake Mechanism Replacement, Improvement, and Operation

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Parking brake lever in the UP engaged position.  The red incandescent bulb is 28 volts, however, a 12 volt bulb can be used.  Throttle is Boeing OEM

As part of the throttle quadrant rebuild, the parking brake system was enhanced.  In the previous system, the parking brake lever was controlled by a relay and a 12 volt solenoid.  The system worked well, however, there were some minor differences between the simulated system and that of the system used in the real Boeing aircraft.

Furthermore, as it was predominately a software system, any change to the avionics suite would affect its operation.

To 'get a handle on' the mechanical linkages used, please read the article regarding the previous system 737 Parking Brake Mechanism.

Revamped System

There has been minimal alteration to the mechanical system, with the exception that the solenoid has been replaced by a 12 volt actuator, a micro-switch has replaced the toggle switch, and the system now requires the toe brakes to be depressed to engage the parking brake.

The actuator is partially visible; the blue coloured mechanism.  The parking brake vertical control rod, micro limit switch and upper part of the high tensile spring can be to seen to the lower right

What is an Actuator

An actuator is a type of motor that is responsible for moving or controlling a mechanism or system.  It is operated by a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that energy into motion.

Almost every modern automobile has a door lock actuator which is responsible for the locking and unlocking of the door locks.  This website 'How Stuff Works' provides a very good overview of how an actuator works.

The actuator is responsible for maintaining the parking brake lever in the UP position.  This occurs when the circuit is closed and 12 volt power is briefly directed to the actuator to lock the device into the engaged position. 

The actuator used is an automotive door lock actuator - code BOLA-2 by Bullz-Audio (amazon link).

closer view of the mounted acctuator

System Overview

The actuator is the mechanism that enables the parking brake lever to be locked into the UP position.  Without power, the actuator is in the resting position and the parking brake lever is pulled to the DOWN position by a high tensile spring.

The annunciator is mounted horizontally on the Captain-side of the throttle quadrant and is powered by 12 volts.

To connect the actuator to the parking brake system, the following items have been used:

  • An actuator;

  • A micro-limit switch;

  • A relay;

  • A 12 volt power supply and busbar;

  • A standard interface card (Leo Bodnar BU0836A Joystick Controller card); and,

  • Depending upon your requirements (mechanical or part mechanical system), a Phidget 0/0/8 card (1017_1).

Registration of Parking Brake Movement

After the parking brake lever has been wired to the BU0836A card, the card must be registered in Windows.  After this has been completed the parking brake lever can be assigned in ProSim737 (configuration/MCP Throttle Switches), P3D, or via FSUPIC.

Relay and Micro-Switch

Two items are used to control whether power enters the circuit: a double throw relay and a micro-switch.

The relay is connected to the toe brakes, and when the brakes are depressed, the relay will close.  When the brakes are released the relay will open.  The connection of the relay to the toe brakes can be done a number of ways, but probably the easiest way is to install a button or micro-switch to the toe brakes.  A Phidget 0/0/8 card can also be used, but this method is slightly more convoluted.

The relay (open/closed) is triggered by the movement of the toe brakes.

A micro-switch is used to open or close the circuit when the parking brake lever is raised or lowered.

The micro-switch is mounted proximal to the vertical control rod, and when the parking brake is is in the DOWN position, the connectors from the micro switch are touching a flange that has been attached to the rod, however, when the parking brake lever is moved to the UP position, the connection is severed (circuit open or closed). 

The use of a micro-switch facilitates a second line of containment.  What this means is that the mechanism will only function fully when the relay is closed (toe brakes depressed) and the micro-switch is closed (parking lever raised).

The relay, either enables or inhibits 12 volt power to flow into the circuit, and this is dependent upon the whether the toe brakes are depressed.

The reason for this set-up will be understood shortly.

Toe Brakes

In the real aircraft, the parking brakes can only be engaged or disengaged when the Captain-side or First Officer-side toe brakes are depressed.  This mechanical system has been faithfully replicated by using a relay, micro-switch and actuator.

How It Works

The actuator will only engage when the toe brakes are depressed.  This means that the parking brake cannot be engaged (lever locked in the UP position with red annunciator on) or disengaged (lever in DOWN position with red annunciator off) unless the toe brakes are depressed. 

Depressing or releasing the toe brakes closes or opens the relay which in turn enables 12 volt power to reach the annunciator via the busbar.  However, the system is only 'live' (closed system) when the parking brake lever is moved to the UP position, enabling power to flow unhindered through the circuit.  When the toe brakes are released, the circuit is open and the actuator remains in the engaged locked position with the parking brake lever locked in the UP position.

To release the parking brake lever, the opposite occurs.  When the toe brakes are depressed, the relay opens directing power to the actuator which disengaged the actuator lock.  The parking brake lever is then pulled to the DOWN position by the tensile spring.

How To Engage The Parking Brake

The method used to engage the parking brake is as follows:

  1. Slightly depress the toe brakes.  This will open the relay and enable 12 volts to engage the actuator;

  2. Raise the parking brake lever to the UP position and hold it in this position; and,

  3. Release the toe brakes.  Releasing pressure on the toe brakes causes the actuator to lock into the engaged position, as the power ceases to flow to the actuator.

To release the parking brake, the toe brakes are depressed.  This will cause the actuator to unlock and return to its resting position.  The high tensile spring will pull the parking brake lever to the DOWN position with a loud snapping sound.

More Ways To Skin A Cat - Full Mechanical or Part-Mechanical

There are several methods that can be used to connect the actuator to the parking brake mechanism. No one method is better than the other.  I have outlined two methods.

(1)   Mechanical Method: This has been described above.

The toe brakes are connected to a relay (via micro-switches, buttons or whatever) and then connected with a busbar/12 volts power source, micro switch, and finally the actuator. 

Other than  connection of the parking brake lever to an interface card, and registration of the movement of the parking brake lever (either in ProSim-AR, FSX, or via FSUIPC) this method requires minimal software.

(2)  Part-mechanical/Software Controlled: This involves using the USER section in the configuration menu within ProSim-AR.

A Phidgets 0/0/8 relay card is connected to ProSim-AR and the the USER interface located in the configuration/switches menu of ProSim737 is programmed to read the movement for the toe brakes.  In this example USER 1 has been selected.  This process removes the need to install a micro-switch or button to the toe brakes.

Each USER IN has a corresponding USER OUT and this is located in GATES.  Opening Configuration/Gates, the same USER number is found (USER 1).  In the tab beside USER 1 the output from the Phidgets 0/8/8 card is entered.  Therefore, whenever USER 1 is triggered, there will be a corresponding output.

When the toe brakes are depressed, the software will read the movement and send a signal to the Phidget card to engage the relay.  This in turn will enable the busbar to be powered and the micro-switch to receive power.  Whether the parking brake lever is engaged (UP) or disengaged (DOWN) will open or close the micro-switch (closing or opening the circuit).  

The actuator will be engaged (circuit closed) only if the micro-switch (located on the vertical rod mentioned earlier) connection is severed (parking brake lever is in the raised position closing the circuit).

Actuator Power and Caution LED

The actuator, powered by 12 volts is connected to the 12 volt busbar in the Throttle Communication Module (TCM) and then, via a straight-through cable, to the Throttle Interface Module (TIM).  The relay for the parking brake mechanism is located in the TIM.

The design of an actuator is such, that if power is continuously applied to the mechanism, it will burn out.  If operating correctly, the actuator will onlt receive power when the toe brakes are depressed and the parking brake lever is raised at the same time.

To combat against the unforeseen event of power being continuously supplied to the actuator, for example by a relay that is stuck in the open (on) position, a coloured LED has been incorporated into the three LEDs that are fitted to the front of the Throttle Communication Module (TCM).  This flashing purple coloured LED illuminates only when the circuit is closed and the actuator is receiving 12 volt power.

Important Point:

  • Two terms often confused are open circuit and closed in relation to an electrical circuit.

Any circuit which is not complete is considered an open circuit.  Conversely, a circuit is considered to be a closed circuit when electricity flows from an energy source to the desired endpoint of the circuit.

Conversely, a closed relay means it allows voltage to travel through it, while an open relay is the opposite.

Additional Information

Like many things, there are several ways to accomplish the same or a similar task.  The following posts located in the ProSim737 forum discuss the conversion of the parking brake lever.

  • This article is one of several pertaining to the conversion of the OEM Throttle Quadrant. 

  • NOTE:  Since publication, ProSim-AR has incorporated into their software a parking brake release 'command'.  This by-passes the need to use the USER OUT settings mentioned above.  The command is set to the output on the Phidget 0/0/8 card.  The parking brake release can be found in the Configuration/Gates menu.  (MORE TO COME - in construction).

Throttle Quadrant Rebuild - Speedbrake Motor and Clutch Assembly Replacement

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The motor that provides the power to move the speedbrake lever is attached via a slipper clutch to the speedbrake control rod. The slipper clutch can easily be adjusted and if set correctly provides the correct torque required for the speedbrake lever to move.   Below the motor is the Throttle Communication Module (TCM) that accommodates, amongst other things, the relays that are used by the logic to control the speedbrake lever's movemen

The mechanics of the speedbrake system has been completely overhauled, however, the logic that controls the speedbrake has remained ss it was. 

Several problems developed in the earlier conversion that could not be successfully rectified.  In particular, the speed of the speedbrake lever when deployed was either too fast, too slow, or did not move at all, and the clutch mechanism frequently became loose. 

Other minor issues related to the condition korrys that illuminate when the speedbrake is either armed or extended; these korrys did not always illuminate at the correct times.

The slipper clutch can easily be adjusted and if set correctly provides the correct torque required for the speedbrake lever to move.   Below the motor is the Throttle Communication Module (TCM) that accommodates, amongst other things, the relays that are used by the logic to control the speedbrake lever's movement.

Rather than continually‘tweak the earlier system, it was decided to replace the motor and clutch assembly with a more advanced and reliable system. To solve the arming issue, a linear throw potentiometer has been used to enable accurate calibration of the speedbrake lever in Prosim737.

Important Point:

  • To read about the first conversion and learn a little more about closed-loop systems and how the speedbrake works, please read the companion article PRIOR to reading this article.  This article only addresses the changes made to the system and builds on information discussed in the other article: 737 Throttle Quadrant  Speedbrake Conversion and Use. 

Motor and Clutch Assembly

A 12 volt motor is used to power the speed brake.  The motor is mounted forward of the throttle unit above the Throttle Communication Module (TCM).  The wiring from the motor is routed, in a lumen through the throttle firewall to a 12 volt busbar and relays.  The relays, mounted inside the TCM, are dedicated to the speedbrake. 

Attached to the 12 volt motor is a slipper-clutch assembly, similar in design to the slipper clutches used in the movement of the two throttle thrust levers.  The clutch can easily be loosed or tightened (using a pair of padded pliers) to provide the correct torque on the speedbrake lever, and once set will not become loose (unless exposed to constant vibration). 

diagram 1: slipper clutch cross section

The slipper clutch and bearings have been commercially made.

A linear throw potentiometer has been mounted on the Captain-sid of the quadrant.  The potentiometer enables the movement of the speedbrake lever to be finely calibrated in ProSim737

Speedbrake Mechanics

In the real Boeing 737 aircraft, buttons are located beneath the metal arc that the speedbrake travels.  If you listen carefully you can hear the buttons clicking as the lever moves over the button.  These on/off buttons activate as the speedbrake lever travels over them, triggering logic that causes the speedbrake to move.

This system has been replicated by using strategically placed micro-buttons beneath the speedbrake lever arc.  As the speedbrake lever moves over one of the buttons, the button will trigger a relay to either open or close (on/off).  The four relays, which are mounted in the Throttle Communication Module (TCM) trigger whether the speedbrake will be armed, stowed, engaged on landing, or placed in the UP position.

Speedbrake Korry (armed and extended)

The speedbrake system is a closed system, meaning it does not require any interaction with the avionics suite (ProSim737), however, the illumination of the condition lights (speedbrake armed and extended on the MIP) is not part of the closed loop system.  As such, the korrys must be configured in ProSim737 (switches/indicators). 

An easy workaround to include the arm korry to the closed loop system is to install a micro-switch under the speedbrake lever arc to correspond to the position of the lever when moved to the armed position.  Everytime the level over the micro-switch the arm korry will illuminate.

Speedbrake Operation

To connect the mechanical system to the avionics (ProSim737), a linear throw potentiometer has been connected to a Leo Bodnar BU0836A Joystick Controller card.  This enables the movement of the speedbrake lever to be calibrated in such a way that corresponds to the illumination of the korrys and the extension of the spoilers on the flight model.  The potentiometer has been mounted to the throttle superstructure on the Captain-side.

Using a potentiometer enables the DOWN and ARM positon to be precisely calibrated in ProSim737 (config/configuration/combined config/throttle/mcp/Levers).

The following conditions will cause the speedbrake lever to deploy from the DOWN to the UP position.

  1. When the aircraft lands and the squat switch is activated;

  2. During a Rejected Takeoff (RTO).  Assuming the autobrake selector switch has been set to RTO, there is active wheel spin, and the groundspeed exceeds 80 knots; and,

  3. If the reverse thrust is engaged with a positive wheel spin and a ground speed in excess of 100 knots.

Point (iii) is worth expanding upon.  The speedbrake system (in the real aircraft) has a built-in redundancy in that if the flight crew forget to arm the speedbrake system and make a landing, the system will automatically engage the spoilers when reverse thrust is engaged.  This redundant system was installed into the Next Generation airframe after several occurrences of pilots forgetting to arm the speedbrake prior to landing.  

Therefore, the speedbrake will deploy on landing either by activation of the squat switch (if the speedbrake was armed), or when reverse thrust is applied.

Speedbrake Logic ( programmed variables)

The following variables have been programmed into the logic that controls the operation of the speedbrake.

  1. Rejected Take Off (RTO).  This will occur after 80 knots call-out.  Spoilers will extend to the UP position  when reverse thrust is applied.  The speedbrake lever moves to UP position on throttle quadrant.  RTO must be armed prior to takeoff roll;

  2. Spoilers extend on landing when the squat switch is activated.  For this to occur, both throttle thrust levers must be at idle (at the stops).  The speedbrake lever also must be in the armed position prior to landing.  The speedbrake lever moves to UP position on throttle quadrant;

  3. Spoilers extend automatically and the speedbrake lever moves to the UP position when reverse thrust is applied;

  4. Spoilers close and the speedbrake lever moves to the DOWN position on throttle quadrant when the thrust levers are advanced after landing (auto-stow); and,

  5. Speedbrakes extend incrementally in the air dependent on lever position (flight detent).

The logic for the speedbrake is 'hardwired' into the Alpha Quadrant card.  The logic has not changed from what it was previously.

Speedbrake Lever Speed

When the speedbrake lever is engaged, the speed at which lever moves is quite fast.  The term ‘biscuit cutter’ best describes the energy that is generated when the lever is moving; it certainly will break a biscuit in two as well as a lead pencil.  Speaking of lead pencils, I have been told a favorite trick of pilots from yesteryear, was to rest a pencil on the throttle so that when the speedbrake engaged the pencil would be snapped in two by the lever!

The actuator that controls the movement of the speedbrake.  This image was taken from beneath the floor structure of a Boeing 600 aircraft.  Image copyright to Karl Penrose

In the real Boeing 737 aircraft the movement of the lever is marginally slower and is controlled by an electrically operated actuator (28 volts DC). 

In theory, the moderate speed that the speedbrake lever moves in the real aircraft should be able to be duplicated; for example, by suppressing the voltage from the 12 volt motor by the use of a capacitor, using a power supply lower than 12 volts, or by using speed controllers.  These alternatives have yet to be trailed.

It is unfortunate, that most throttle quadrants for sale do not include the actuator.  The actuator is not part of the throttle unit itself, but is located in the forward section under the flight deck.  The actuator is then connected to the speedbrake mechanism unit via a mechanical linkage.

In the real aircraft, the speedbrake lever and actuator provide the input via cables, that in-turn actuate the speedbrakes.  There is no feedback directly from the hydraulics and all operation is achieved via the manual or electric input of the speedbrake lever.

Actuator Sound

The sound of the actuator engaging can easily heard in the flight deck when the speedbrake engages (listen to the below video).  To replicate this sound, a recording of the actuator engaging was acquired.  The .wav sound file was then uploaded into the ProSim737 audio file library and configured to play when the speedbrake is commanded to move (squat switch).  

The .wav file can be shortened or lengthened to match the speed that the lever moves. 

Synopsis

I realize this and the companion article are probably confusing to understand.  In essence this is how the speedbrake operates:

  • A potentiometer enables accurate calibration (in ProSim737) of the DOWN and ARM position of the speedbreak lever.  This enables the condition korrys to illuminate at the correct time.

  • Micro-buttons have been installed below the arc that the speedbrake lever travels.  The position of each button, is in the same position as the on/off buttons used by Boeing  (the buttons are still present and you can hear them click as the speedbrake lever moves across a button).

  • The speedbrake system is a closed-loop system and does not require ProSim737 to operate.

  • The logic for the system has been programmed directly into the Alpha Quadrant card mounted in the Throttle Interface Module (TIM).  This logic triggers relays, located in the Throttle Communication Module (TCM) to turn either on or off as the speedbrake lever travels over the micro-buttons.  This is exactly how it's done in the real aircraft.

  • The micro-buttons are connected to a Phidget 0/0/8 relay card (4 relays).  The relay card is located within the Throttle Communication Module (TCM).

  • The speedbrake moves from the ARM position to the UP position when the squat switch is triggered (when the landing gear touches the runway).  The squat switch is a configured in ProSim737 (configuration/combined configuration/gate/squat switch).

Video

The upper video demonstrates the movement of the speedbrake lever.    The lower video, courtesy of U-Tube, shows the actual movement of the lever in a real Boeing aircraft.

The video is not intended for operational use, but has been shown to demonstrate the features of the speedbrake system.

If you listen carefully to both videos, you will note a difference in the noise that the actuator generates.  I have been informed that the 'whine' noise made by the actuator is slightly different depending upon the aircraft frame; the actuator in the older classic series Boeing being more of a high whine in comparison to the actuator in the Next Generation aircraft.

 

737-500 automated speedbrake deployment

 
 
 

Glossary

  • Condition(s) - A term referring to a specific parameter that is required to enable an action to occur.

  • FSUIPC - Flight Simulator Universal Inter-Process Communication.  A fancy term for software that interfaces between the flight simulator programme and other outside programmes.

  • Speedbrake Lever Arc - The curved arc that the speedbrake lever travels along.

  • Updated 11 July 2020.

B737 Original Equipment Manufacture RMI Knobs Fully Functional

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oem rmi knobs mounted to the potentiometers that control the rmi

In two previous posts, I documented the installation of two bespoke reproduction RMI knobs and aN OEM ADF/VOR switch assembly mounted in the center pedestal.  The purpose of the switch assembly, which originally was used in a Boeing 727 airframe, was to provide an easy method to switch between ADF and VOR as the two knobs mounted on the RMI were non-functional.

With the acquisition of OEM RMI knobs, the next step was to implement the functionality of these knobs by installing micro-rotary switches to the RMI frame behind each knob.  The non Next Generation compliant RMI Switch Assembly panel would then be superfluous and removed from the center pedestal.

Installing the Micro-rotary Switches to the RMI Frame

The first step was to remove the RMI frame from the MIP and enlarge the holes that the RMI knobs reside.  This is to allow the installation of the two micro-rotary switches. To do this, a Dremel rotary tool was used.   

To enable the wires from the rotary switches to be routed neatly behind the RMI frame, a very narrow trench was cut into the rear of the plastic frame.  It is very important that this task is done with due diligence as the RMI frame produced by Flight Deck Solutions (FDS) is manufactured from ABS plastic and not metal – if the cut is too deep or too much pressure is applied to the Dremel, then the frame will be damaged.

The wires from the the RMI knobs are then laid inside the earlier cut trench and aluminum-based tape is  applied over the wires.  This ensures the wires are secure and do not dislodge from the RMI frame.

The micro-rotary switches used in this conversion are 1 cm in length (depth); therefore, to use these rotaries successfully you will need to have a certain amount of airspace between the rear of the RMI frame and front of the computer screen (central display unit).  Whether there is enough room to facilitate the installation of the rotary switch, will depend upon the manufacturer of the MIP and RMI frame – some manufacturers have allowed a centimeter or so of space behind the RMI frame while others have the frame more or less flush to the center display unit screen.  If the air space is minimal, the rear of the rotary may rub against the display unit.

RMI frame and OEM knobs connected to small rotary potentiometers.  Note the metal sleeve and grub screw in the knob.

There are several methods that can be used to secure the rotaries to the RMI frame.  By far the easiest is to enlarge the hole in the RMI frame to a diameter that the rotary can be firmly pushed through the hole and not work its way loose.  Another method, more permanent, is to glue the rotary inside the hole.  No matter which method used, the rotary must be secured inside the hole otherwise when the RMI knob is turned the rotary will swivel within the hole.

Once the rotaries are installed to the frame, the OEM knobs are carefully pushed over the rotaries and the metal grub screws on the knob tightened.  One of the benefits of using OEM knobs is that the inside of the knob has a metal sleeve which ensures that the knob will not wear out and slip with continual use – reproduction knobs rarely are manufactured with an inside metal sleeve.

Interface Card and Configuration

To enable functionality, the wires from the rotaries are carefully threaded through the MIP wall and routed to an interface card; A PoKeys card, mounted in the System Interface Module (SIM), has been used.  It is not necessary to use a large gauge wire to connect the rotaries to the interface card.  This is because the electrical impulse that travels through the wire is only when the RMI knob is turned, and then it is only for a scone or so.  

The functionality for the RMI knobs is configured within the ProSim737 avionics suite in the configuration/switches area of the software.

Micro-rotary Switches

There are several micro-rotary switches available in the market.  This conversion uses A6A sealed rotary DIP switches; they are compact and inexpensive.

When selecting a rotary, bear in mind that many rotaries are either two, three or four clicks in design.  This means that for a 90 degree turn, such as required when altering the RMI from VOR to ADF, the rotary will need to travel through a number of clicks to correspond with the visual position of the switch.

The A6A type mentioned above are a two click type.  The first click will change the designation (VOR to ADF or back again), however, for realism two clicks are made (90 degree turn).  At the time of the conversion it was not possible to find a small enough rotary that was one click.  Despite this shortcoming, the physical clicks are not very noticeable.

This conversion is very simple and is probably one of the easiest conversions that can be done to implement the use of OEM knobs.  There is minimal technical skill needed, but a steady hand and a good eye is needed to ensure the RMI frame is not damaged when preparing the frame for the installation of the two rotary switches.

oem rmi knobs in original plastic bag. note metal inner sleeve and grub screw

OEM RMI Gauge

This  conversion uses two OEM RMI knobs and rotaries to interface with the standard virtual RMI gauge provided within the ProSim737 avionics suite.  Converting an OEM RMI gauge for standalone operation is possible and has been accomplished by other enthusiasts; however, whether a full RMI conversion can be done very much depends upon your particular simulation set-up.

If a OEM RMI gauge is installed, there may be a spacing issue with the other alternate gauges.  In particular, the Integrated Standby Flight Display (ISFD) will require a smaller dedicated display screen.  Likewise, the EICAS display screen will need to be smaller so as to fit between the RMI gauge and the landing gear assembly.  Also, an extra display port will be required for the computer to read the ISFD display screen. 

Certainly, a complete conversion of a RMI gauge is the best way to proceed, if you already own a OEM RMI unit, and if the set-up problems are not too difficult to overcome.

Acronyms

  • MIP – Main Instrument Panel

  • OEM – Original Equipment Manufacturer

  • RMI – Radio Magnetic Indicator

OEM Annunciators Replace Reproduction Korrys in Main Instrument Panel (MIP)

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There can be little doubt that OEM annunciators shine far brighter than their reproduction counterparts.  The korrys are lit during the lights test. OEM Flaps gauge yet to be installed

A task completed recently has been the replacement of the reproduction annunciators located on the Main Instrument Panel (MIP) with OEM annunciators. 

The reason for changing to OEM annunciators was several-fold.  First, anything OEM is superior to a reproduction item.  Second, I wanted to reproduce the same korry annuciation  lighting observed in the OEM panels in the center pedestal, fire suppression panel, and when fitted, the forward and aft overhead panels.  Additionally, it was also to enable the push-to-test functionality and to provide better illuminance during daylight.  Some reproduction korrys are not that bright when annunciated and are difficult to see during the day.

This post will explain the anatomy of the annunciators that are fitted to the Main Instrument Panel (MIP).  It will also detail how the annunciators are wired and configured in ProSim737, and provide incite into some of the advantages and functionality that can be expected when using OEM annunciators.

The individual indexing can be observed on the top surface of the upper assembly (3 groves).  To separate the two assemblies a hex screw must be used to loosen the hex screw located inside the brass-coloured circular fitting.  Note that this is a new style LED korry which does not support the older incandescent bulbs

Anatomy of a Annunciator (Korry)

An annunciator is a light which is illuminated when a specific function occurs on the aircraft.  Annunciators are often called by the generic name ‘Korry’, as Korry is the registered trademark used by a company called Esterline that manufactures annunciators for the aero and space industry. 

There are two types of annunciators used in the Boeing aircraft, the 318 and the 319 which are either a Type 1 or Type 2 circuit. 

The 318 and 319 Korrys are not interchangeable.  Each Korry has a different style of bulb, differing electrical circuits, and a different method of internal attachment (captive hex screw verses two blade-style screws).  The only similarity between the 318 and 319 korrys is that the hole needed to house the korry in the MIP is identical in size - .440” x .940”.  The 318 Korry replaced the 319 Korry.

The circuit type refers to the electrical circuit used in the Korry.    Both circuit types require a ground-controlled circuit to turn it on, however, Type 1 circuits are ground-seeking while Type 2 circuits are power-seeking.    Visually (when installed to the MIP) the 318 and 319 korrys are indiscernible.

Annunciators have five parts that comprise:

(i)     The lower assembly and terminals (usually four terminals in number);

(ii)    The upper assembly;

(iii)    The outer housing/sleeve which has a lip to allow a firm connection with the MIP;

(iv)    The push-in light plate which includes the bulbs; and,

(v)    The legend, which incorporates a replaceable coloured lens.

The four terminal connections on the rear of each annunciator are specific to the functionality of the unit.  Each will exhibit a differing circuit dependent upon its function.  Likewise, each annunciator is individually indexed to ensure that the upper assembly cannot be inadvertently mated with the incorrect lower assembly.

Annunciators typically are powered by 28 Volts, use two incandescent ‘push-in style’ bulbs, and dependent upon the korry’s function, may have a light plate coloured amber, white red or green.  The legend is the name plate, and legends are usually laser engraved into the light plate to ensure ease of reading.  The engraved letters are in-filled with colour to allow the printing to stand out from the light plate’s lens colour.

Specialised Korry

The Boeing 737 aircraft uses a Korry, a type 318, that is slightly different to the standard Korry. This Korry enables the functionality for the BELOW G/S – P-Inhibit function.  

The Type 318 differs from other korrys used in the MIP in that it has a dry set of momentary contacts which are controlled by pressing the light plate.  Pressing the illuminated light plate extinguishes the annunciator and cancels the aural ‘Below Glideslope’ caution.

Reproduction Verses Original Equipment Manufacture (OEM)

The four biggest differences between reproduction and OEM annunciators are:

(i)     The ability to depress the light plate in the OEM unit for Push-To-Test function;

(ii)    The ability to replicate specific functions, for example the Below G/S P-Inhibit korry;

(iii)    The hue (colour) of the lens and crispness of the legend; and,

(iv)    The brightness of the annunciator when illuminated (5 volts verses 28 volts).

Reproduction Korry Shortfalls

Two areas lacking in reproduction units is the brightness of the annunciator when illuminated, and poorly defined legends.  

For the most part, reproductions use 5 volts to illuminate two LEDS located behind the lens.  Whilst it is true that the use of LED technology minimises power consumption and heat generation, the brightness of the LEDS, especially during the day,  may not be as bright as the two 28 volt incandescent bulbs used in an OEM annunciator.   Moreover, 5 volts does not allow the successful use of DIM functionality.  

It is unfortunate that many lower priced annunciators also lack well defined engraved lens plates making the ability to read the annunciator legend difficult at best.

Shortfalls notwithstanding, most high-end reproduction annunciators are of high quality and do the job very well.  

 

Table 1: quick reference to determine the main differences between OEM and reproduction annunciators. Note that the appearance of the annunciator can alter markedly between different manufacturers of reproduction units

 

Installation, Interfacing and Configuration of OEM Annunciators

Replacing a reproduction annunciator with its OEM counterpart is straightforward if the Main Instrument Panel (MIP) has been produced 1:1; however, reproduction MIPs are rarely exactly 1:1 and in all probability you may need to enlarge the hole that the annunciator resides.  If this is the case, ensure you use a fine-grade aluminum file and gentle abrade the hole to enlarge it.  When enlarging the hole, ensure you continually check the hole size by inserting the korry – if the hole is enlarged too much, the korry will be loose and will require additional methods to secure to the MIP.

korry system 318 type 1

Disassembling a Korry

It is important to understand how to unassemble the annunciator.  

First, the light plate has to be gently pried loose from the upper assembly.  Once this is done, the upper and lower assemblies must be separated to allow the outer/sleeve to be removed.  The Type 318 annunciators have a hex screw, located in the lower assembly unit, which needs to be loosened with a 5/64th hex wrench to allow separation, while the Type 319 annunciators are secured by two standard screws that require a small blade screwdriver.  

Once the two parts are separated, it should be noted that the upper assembly has a flange at the forward end; this flange enables the annunciator to be firmly connected to the MIP.   

Attaching a Korry to the MIP

Is your MIP 1:1 and will it fit OEM korrys without further to do?  Click the diagram to see the dimensions of korrys (with thanks to Mongoose for diagram)

Insert the upper assembly into the MIP flange facing forward.  Next, slide the housing over the rear of the mechanism from the rear of the MIP.  Rejoin the lower section and tighten the hex screw.    If the MIP is 1:1, the annunciator should now be firmly secured to the MIP wall. The light plate can now be pushed into the mechanism.

If the annunciator does not fit firmly into the MIP, it can be secured by using silastic or a glue/metal compound.  (I do not recommend this.  It is best to ensure the hole is the correct size or a tad too small.  This will guarantee that the annunciator will have a firm fit).

Provided the mechanism is not faulty or does not break, the chance that it will need to remove it is very remote.  If the bulbs fail, they are easily replaced as they are contained within the light plate.

Wiring - Procedure

Wiring the MIP annunciators is a convoluted and repetitious process that involves daisy-chaining the various annunciators together.  Because wiring is to and from four terminals, it can be difficult to remember which wire goes where.  As such, it is recommended to use coloured wire, label each wire and keep meticulous notes.  

Each annunciator has four terminals located on the rear of the unit that corresponds to:

(i)      Positive (28 volts);

(ii)     Logic for the function of the korry;

(iii)    Lights test; and,

(iv)    Push-To-Test.  

To crosscheck the above, each Type 2 korry has a circuit diagram stenciled on the side of the assembly.

 

Figure 1: A schematic of the three types of korrys used in the Boeing 737.  The left diagram is from the 318 push to inhibit korry (diagram copyright David C. Allen

 

For the OEM korrys to function correctly, they need to be connected with an interface card (I/O card).  An example of such a card is a Phidget 0/16/16 card.

(i)    Designate the annunciator closest the I/O card and power supply as the lead annunciator (alpha).  

(ii)    Terminal 1 and Terminal 4 are the power terminals for each korry.  Connect to the alpha korry the positive wire from the 28 Volt power supply to terminal 1 and the 28 Volt negative wire to terminal 4.  The wires from these two terminals are then daisy-chained to the identical terminals on the other korrys in the system.

(iii)    Terminal 2 controls the logic behind the function for each korry.  A wire must connect from terminal 2 of each korry to the output side of the I/O card.  To close the loop in the I/O card, a wire is placed from 28 Volts negative to the ground terminal on the card (input).

(iv)    Terminal 3 controls the logic behind the light test toggle.  A wire is daisy-chained from terminal 3 of the alpha korry to all other korrys in the system.  A wire is then extended from the final korry to the lights test toggle switch.  This switch has been discussed in detail in a separate post.

Quite a bit of wire will be needed to connect the thirteen or more annunciators and it is a good idea to try and keep the wire neat and tidy by using a lumen to secure it to the rear of the MIP.

Mounting and Brackets

Every simulator design is different, and what is suitable for one set-up may not be applicable to another.  

The I/O card that is used to control the MIP annunciators is mounted within the System Interface Module (SIM).  To this a straight-through cable is securely attached that connects to a D-Sub connector mounted on an aluminum bracket.  The bracket and two terminal blocks are strategically mounted on the rear of the MIP and enable the various wires from the korrys to connect with the straight-through cable.

Interfacing and Configuration Using ProSim737

To interface the annunciators, follow the directions on how to wire your I/O card.

This article provides information on the Phidget 21 Manager (software) and how a Phidget interface card is used.

If the annunciators have been correctly daisy-chained together, only the wires from terminal 2 of each korry will need to be connected to Phidget card.  When power is applied, the Phidgets software will automatically assign outputs to any device (korry) attached to the 0/16/16 card.  

To determine the digital output number for each annunciator, open the Phidgets 21 Manager, push the light plate on a chosen annunciator and record the allocated output number.  The output numbers are used by ProSim737 to allocate that annunciator to a specific software command line.  

Configuring the MIP annunciators in ProSim737 is a two-step process.  First, the annunciator must be assigned as a switch (for the puhs- to-test function to operate), then as an indicator (for the annunciator to illuminate).  Before commencing, check that Phidgets have been assigned in the driver section of the configuration section of the main ProSim737 menu.  

Open the configuration screen and select switches and scroll downwards until you find the appropriate switch that corresponds to the annunciator.  Assign this switch to the output number assigned by the Phidgets software (If you have multiple Phidget cards installed ensure the correct card is assigned).  

After this has been completed, continue the configuration process by assigning each annunciator to the appropriate indicator in the configuration/indicators section.

Lights Test

A lights test is used to determine whether all the annunciators are operating correctly.  A lights test can be accomplished two ways. 

The first method is to press the light plate of an annunciator which operates a momentary switch that causes the light to illuminate (push-to-test).  This is an ideal way to determine if an individual annunciator is working correctly.

The second method is to use the MIP toggle switch.  Engaging the toggle switch to the on position will illuminate all the annunciators that are connected to the toggle switch.  This is an excellent way to ensure all the annunciators are operational and is standard practice before beginning a flight.

It should be noted that for all the annunciators to illuminate, each korry must be connected to the toggle switch. 

An earlier post explained the conversion and use of a OEM Lights Test Toggle Switch.

The fire suppression panel annunciators are also korrys.  Like their MIP sisters, the korrys are very bright when illuminated as they are powered by 28 volts

Korry Systems

This post has discussed the main annunciators on the MIP which is but one system.  Other systems include the annunciators for the forward and aft overhead annunciators, fire suppression panel and several other panels.

To connect additional systems to the enable a full lights test to be done, an OEM aircraft high amperage relay can be used.  

OEM multi-relay device.  The relay from a Boeing aircraft is not necessary; any aircraft relay will suffice.  It's wise to choose a relay that has multiple connection posts as this will enable different systems to be connected to the relay.  The relay is easily fitted to the rear of the MIP or to the inside of the center pedesta

Depending upon the type of relay device used (there are several types), it may be possible to connect up to three systems to the one relay.  This is made possible by the OEM toggle switches unique multi-segment system, and the ability of the relay to handle high amperage from multiple aircraft systems.

A benefit of using an OEM relay is that it provides a central point for all wires from the various systems to attach, before connecting to the lights test toggle switch.  Note that 28 volts bmust be connected directly to the relay for correct operation.

The relay will, depending upon the throw of the toggle switch (lights test), open or close the circuit of the relay.  Opening rhe relay circuit (when the light test toggle is thrown) enables 28 volts to flow through the relay and illuminate any annunciators connected to the system.

Availability

The Korrys originally were used in British Airways 737-400 Airframe 25843

Fortunately, apart from a few functions, there is little difference between older style annunciators used in the classic series airframes and those used in the Next Generation aircraft - an annunciator is an annunciator no matter from what airframe (100 series, Classic or Next Generation).

Annunciators are relatively common and are often found ion e-Bay.  However, to acquire a complete collection that is NG compliant can be time consuming, unless a complete panel is purchased and the annunciators removed.

Lineage

The annunciators used in the simulator came from a B737-400 airframe.   This aircraft - serial number N843BB and construction number 25843 had a rather interesting lineage. 

It began service life in March 1992 with British Airways as G-DOCM before being transferred to Fly Dubai and Air One in 2004.  Late 2004 the airframe was purchased by Ryan International and the registration changed to N843BB.  Between 2005 and 2010 the aircraft was leased to the Sundowner LCC who at the time was contracted to the US Dept. of Justice.   The aircraft was returned to Ryan International mid 2010 and subsequently scrapped.

Acronyms