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Mission Statement 

The purpose of FLAPS-2-APPROACH is two-fold:  To document the construction of a Boeing 737 flight simulator, and to act as a platform to share aviation-related articles pertaining to the Boeing 737; thereby, providing a source of inspiration and reference to like-minded individuals.

I am not a professional journalist.  Writing for a cross section of readers from differing cultures and languages with varying degrees of technical ability, can at times be challenging. I hope there are not too many spelling and grammatical mistakes.


Note:   I have NO affiliation with ANY manufacturer or reseller.  All reviews and content are 'frank and fearless' - I tell it as I see it.  Do not complain if you do not like what you read.

I use the words 'modules & panels' and 'CDU & FMC' interchangeably.  The definition of the acronym 'OEM' is Original Equipment Manufacturer (aka real aicraft part).


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Journal Archive (Newest First)

Entries in Real Aircraft Parts (5)


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

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

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

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.  Certain reproduction korrys are not that bright when annunciated and are diffiucult 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.

Anatomy of a Annunciator

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

There are two types of annunciators used in the Boeing aircraft, the 318 and the 319 which are either a Type 1 circuit or a 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 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.    Typically, a Boeing 737 uses Type 1 circuits.

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.

LEFT:  A disassembled annunciator showing the main components (click to enlarge).

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 Next Generation series of aircraft use 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: provides a 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.

Disassembling a Korry

It is important to understand how to disassemble the annunciator.  

LEFT: The individual indexing can be observed on the top surface of the upper assembly.  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 (click to enlarge).

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

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.

LEFT:  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).

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.

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.

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.

LEFT:  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 (click to enlarge).

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

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 unique multi-segment system that the OEM toggle switch provides and the ability of the relay to handle high amperages from multiple aircraft systems.

LEFT:  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 pedestal.

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.


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 (200 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.


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. 

LEFT:  25843 B737-400 in service with British Airways (click to enlarge).

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.


OEM - Original Equipment Manufacturer (aka real B737 aircraft part)


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

It probably seems an oddity to install into the center pedestal a switch manufactured in 1967 that in all probability was used in a an early model Boeing 737 or more lilely a B727.

My reasoning is quite simple; I enjoy flying using VORS and NDBS, and implementation of this switch allows the stand-by RMI gauge to be used more effectively when using these “older style” navigational aids.  

LEFT:  RMI Switch Assembly dated stamped 1967.  RMI switch has been custom fitted to blanking plate (click image for larger view).

VOR and NDB Flying (NG)

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

The navigation output is duplicated and shown as dual needle movement on the RMI gauge which is the third gauge within the stand-by instrument cluster.  In the real B737 aircraft, the mode of the RMI gauge can be toggled between VOR 1/2 and ADF 1/2 or a combination by the small knobs on the front of the RMI that protrude through the Main Instrument Panel (MIP).  

RMI Knobs

It’s unfortunate that many manufacturers of reproduction Main Instrument Panels (MIPS) do not include functionality to these two small knobs and provide only a 'rough' facsimile of an original knob.   We will will look further at the NG RMI knobs in the next post.

The use of the older style 737 Switch Assembly duplicates the functionality ( if it existed) of the stand-by RMI buttons on the MIP.

Interfacing, Wiring and Blanking Plate

The card was interfaced to Flight Simulator using a PoKeys55 interface card.  In my set-up the PoKeys card resides in the System Interface Module (SIM) and the five wires from the 737 switch were run through a piece of conduit (plastic piping) beneath the platform to the System Interface Module (SIM)  located forward of the MIP.

LEFT:  Early Boeing N737 RMI Switch Assembly showing detail of two switches, Canon plug, wiring harness and front panel (click image for larger view).

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

Canon Plugs - Why Change a Perfect System

The switch assembly included a male Canon plug in very good condition; therefore, it was decided to use the Canon plug system rather than wire separately.  A female Canon plug was purchased from E-Bay and to determine the correct pin outs for the plug a multimeter was used to determine conductivity from each pin in relation to the mode toggled.   A longer wire harness was made to allow the harness to reach the System nterface Module forward of the MIP.  Using Canon plugs keeps the wiring very neat and allows for an easy disconnect should you need to remove the panel from the pedestal.

Blanking Plate

In the Boeing 727 and earlier 737 airframes, the RMI Switch Assembly is mounted within the Main Instrument Panel (from memory).  In this era (circa 1967) modern-style EFIS units had yet to be developed. 

As such, the switch does not require a blanking plate as it’s attached to the MIP by four screws.  To facilitate the switch being installed to the center pedestal, a blanking plate had the center portion cut out using a  dremil cutter.  The switch assembly could then by placed in the cut hole and attached directly into the blaking plate via the four screws.

LEFT:  The RMI Switch Assembly installed to the center pedestal.  Selection can be either ADF1/2, VOR1/2 or a combination.  Switches and panel are backlit by 5 Volts which is the standard voltage used in many panels. In the "real world" this panel would never be seen in three-bay center pedestal.

Mapping Functions

To configure the functionality of the Switch Assembly to ProSim737 was straightforward, as the functions have already been mapped within ProSim's configuration menu.  This is one of the major advantages to using ProSim737 as the avionics suite; many functions have been pre-mapped and you do not need to "delve" into the world of FSUPIC offsets in an attempt to get something working.

Not Standard Airline Order

Although it's not standard NG equipment -  "you would NEVER see this switch panel in a B737 NG", the Switch Assembly is very enjoyable to use and makes using the alternate RMI gauge more user friendly - at least until I add functionality to the NG RMI knobs or aquire a OEM RMI guage. 

In the next post we'll discuss the Next Generation (NG) RMI knobs.

Acronyms & Glossary

ADF – Automatic Direction Finder
Blanking Plate - An aluminium plate used to cover a gap in the pedestal or overhead.  The plate is equipped with DZUS fasteners for attachment to the DZUS rail VOR - Omni Directional Radio Range
EFIS – Electronic Flight Instrument System
IMM – Interface Master Module
MIP – Main Instrument Panel
NDB – Non Directional Beacon
PANEL – Refers to actual avionics module.  Panel and module are interchangeable
RMI – Radio Magnetic Indicator.  The gauge that displays VOR and ADF mode.  Part of B737 NG stand-by instrument cluster


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

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

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

The EVAC panel is from a B737-800 NG and incorporates an arming/off switch, flashing red coloured EVAC annunciation, alarm cancelling pull knob and a piecing alarm (horn). 

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

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

The EVAC panel is an airline option and is not stock standard to the aircraft.

Below is a video showing the panel’s use.


Weber Captain & First Officer Pilot Seats 

A call from DHL Freight logistics alerted me to the fact that another large crate had arrived at the local airport for pick-up.  It was too early for the consignment to be the MIP, so the next contender was cockpit seats.

I wasn’t going to purchase pilot seats until the project was nearing its final phase.  However, genuine B737 seats are becoming more difficult to find in good condition, and when I was offered these seats, I decided to “grab them” for the simulator. 

Boeing aircraft use for the most part two types of aircraft seats: Ipeco and Weber; the former being the more modern seat design with adjustable J-rails.  Personally, I find the Ipeco seats to be rather uncomfortable and the configuring of J-rails can be painful.  Weber seats bolt directly to the floor, so as long as you have the correct measurements for the bolt down locations, there shouldn’t be any further problems.  Both the Ipeco and Weber seats have several seat levers to allow for correct and comfortable positioning.

Weber seat cushions are either manufactured from cloth, which are the seats I have, or they have sheepskin covers sewn over and into the cloth.  At some stage in the future, I may have sheepskins installed over the seats, but at the moment this is a secondary issue.

Apart from some very minor cosmetic issues associated with the plastic molding on the rear of one seat, both seats are in excellent condition.  You have to remember that seats are always in used condition and probably have flown thousands of hours of flight time.  Before their new home in the simulator, they were fitted to a 737-500 series aircraft belonging to South West Airlines. 

LEFT:  I had to collect the seats from DHL Freight.  They were screwed to a pallet and it must have looked a little odd driving home with two cockpit seats in a box trailer.

Minor Overhaul of Flight Officer Seat

Although cosmetically the seats look OK, the right hand seat (flight officer) didn't seem to be operating correctly.  Inverting the seat, I was shocked to see a built up of dirt, grim and dust over the mechanisms that control the movement of seat.  Disassembling the components, I also discovered a broken split pin which was stopping the connecting cable, which controls the vertical rise in the seat, from working.  After cleaning and replacing the broken split pin, I lubricated all the areas requiring lubrication.  PRESTO, the seat now works as it should.

Leg Attachment Points - Four Seat Movements

I was surprised to learn that each seat has 16 attachment points to secure the seat to the floor.  When you alter the position of a Weber seat, especially forward and aft, the pressures exerted on the seat legs are quite severe.  The seat has four movements: back reclining (like in a motor car), vertical rise (upwards lift of about a foot or so in height), under leg lifting and forward and aft seat control.  The last movement is needed as Weber seats do not use rails.

CASA Approved?

I was inspecting the seat feet (called duck feet because of their shape.  You can see these triangular style feet in the upper photograph), when my girlfriend came into the room - she commented "I hope their CASA approved".  The first snipe - no doubt more will come  :)  I dare not try the seat harness....   (CASA is the Civil Aviation Safety Authority in Australia)

Oh and before you ask - yes the seats are very comfortable...

To see more detailed pictures of the seats, navigate to the image gallery.

I will post a separate Journal entry explaining how I intend to attach the seats to the platform base.  I'll also post a short video showing how the seats operate.


"Sticky" Auto Throttle Button - Repaired

I noticed soon after the TQ arrived that the engine number one auto throttle button was a bit “sticky”.  Depressing the button, it would stay pressed in for a few seconds even though pressure had been released.  The A/T buttons are one-way buttons meaning that they are click buttons – click in, release, and click out.  It’s probable that after many hours of service, sweat, dead skin cells and dirt has built up on the inner button behind the spring mechanism; a friend suggested that DNA analysis of the built up debris would probably provide a list of suspect pilots!

Whilst the button was still in place, I attempted to loosen the built up material using a can of pressurised electronic cleaner fluid.  The fluid, I hoped would dislodge any loose material before evaporating.  Unfortunately, this didn’t work in the long run, although once lubricated with the evaporative solvent, the button operated correctly for a short time.


The button is held in place within the throttle handle by a ½ inch circlip.  Beneath the circlip and button there is a spring mechanism that pushes the button out after being depressed.  Using a pair of specialised circlip pliers, I very carefully removed the circlip making sure that the spring mechanism of the circlip didn’t propel my A/T button out the window and into the garden! 

With the circlip removed, the inner portion of the throttle handle slides out revealing the button and attached wiring.  The button is a modular design (shaped to fit inside the thorottle handle) and unfortunately cannot be disassembled further, Therefore, I reassembled the button and sprayed a small amount of silicone spray around the button, allowing the silicone solution to penetrate around the the edge of the button. 

The silicon lubricant (which is non conductive, so there is no issue with power shorting) seems to have solved the problem as the button no longer sticks, however, this is only an interim solution.  I'll search for a replacement button module.  Sometimes the most simple solution will fix your problem!!

No doubt I can purchase a new replacement from Boeing for errr $800.00....  I think not.  Eventually I'll find a disused button module in my travels.   If you find a B737 on the line and note the captain side A/T button has been removed - you know who "stole" it  :)