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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.


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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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Entries in Master Caution System (1)


Below G/S P-Inhibit Annunciator (korry)


The Below Glideslope (G/S) P-Inhibit annunciator (korry) is located on the Main Instrument Panel (MIP).  There are two identical korrys; one on the Captain and the other on the First Officer-side.

LEFT:  Captain-side G/S P-Inhibit korry illuminated during daylight operations.  All OEM korrys can easily be seen during the day, as they are powered by 28 volts that energise two incandescent bulbs.  This korry came from a B737-500 (click to enlarge).

All korrys have a push to test functionality and the G/S P-Inhibit korry is no different in this regard; however, what makes this korry different is its additional ability to inhibit an aural warning and extinguish an annunciator, when the light plate is depressed.  This is what the P of P-Inhibit stands for (P=push).

The korry 318 indicator operates by a dry set of momentary contacts, which are controlled by pressing the annunciator light plate.  The part number for this korry is 318-630-1012-002.

Below G/S P-Inhibit Annunciator - Function

The Below G/S P-Inhibit korry is a radio altitude alert and annunciates when there is deviation in the glideslope during an ILS approach.  If the aircraft deviates more than 1.3 dots below the glideslope, the korry will illuminate amber, followed shortly thereafter by an aural warning ‘glideslope’.

This alerts the flight crew to a deviation in glideslope and a possible fly into terrain situation.  The volume and repetition rate of the aural and visual warning will increase as the deviation from glide slope increases.
However, at times the aural warning is not necessary; therefore, a flight crew can silence the aural warning by pressing the korry.  This will cancel or inhibit the alert if the aircraft is at or below 1000 feet Radio Altitude, but is above 50 feet Radio Altitude (RA).

Warning Lights - GPWS and MCS

The korry is part of the Ground Proximity Warning System (GPWS) which provides for several ground proximity alerts for potentially hazardous flight conditions (modes) involving imminent impact with the ground.  The G/S P-Inhibit korry is addressed in MODE 5 of the GPWS modes.

The GPWS loosely falls within the Master Caution System (MCS) in which various coloured warning lights and aural warnings are generated to reflect certain conditions.  The key to the condition colours are as follows:

•    Red lights – Warning:  Indicate a critical condition that requires immediate action.
•    Amber lights – Caution:  Require a timely corrective action.
•    Blue Lights – Advisory:  Do not require any action by flight crew.
•    Green lights – OK: Indicate a satisfactory or on condition.

The Below G/S P-Inhibit korry is amber coloured; therefore, the caution condition generates a priority of 18 (according to the MCS).


The Below G/S P-Inhibit korry is triggered when the following conditions are met:

•    Excessive deviation below the glideslope.
•    Armed when number 1 glideslope receiver has a valid signal and the aircraft is less than 1000 feet RA.
•    Excessive deviation (1.3 dots) below of an ILS Glideslope between 1000 feet and 150 feet.

Simulation and Configuration

The 318 korry is an OEM aircraft part and must be connected to an interface card that supports 28 volts to enable illumination of the korry.  I have used a Phidget 0/16/16 interface card.  This link will provide information on how to connect the korry to the Phidget card.

There are four aspects that need to be addressed when configuring this korry to operate in the flight simulator.

•    The initial connection of the OEM annunciator to a interface card and power supply;
•    The illumination of the annunciator (amber warning);
•    The playing of the aural call-out (glideslope); and,
•    The cancellation (inhibit) of the illumination and the aural call-out.

Whether the korry operates as intended in the simulator depends primarily upon the avionics suite used.  Certainly, ProSim-AR (using User-Offsets) and Sim Avioincs (using FSUIPC offsets) can be configured to allow the korry to illuminate.  The the push to test and push to inhibit function can also be configured.

However, there is a high probability that only the illumination will work if a reproduction annunciator is used.  The reason being, that stock standard annunciators do not replicate the push to test and push to inhibit functions.

ProSim-AR Configuration

The following instruction should provide enough information for you to configure the 318 korry in ProSim-AR.

  • configuration/switches - Register the korry by pressing the annunciator and recording the number displayed (*).
  • open Phidgets library - Open the correct Phidgets card - Click (check) each of the outputs until the korry illuminates.  Remember this output number (**)
  • configuration/indicators - Scroll until you find the glideslope function.  From the menu call-out box select the correct Phidget card number and then select the correct output number (from earlier step marked**).
  • configuration/gates - Scroll to you find the audio call-out 'Glideslope'.  Open the menu call-out box and select the correct Phidget card and the correct output (*).

Classic and NG Differences

The function of the korry used in the classic and NG series airframes is identical.  However, there are differences in appearance.  The classic has a yellow bulb colour when activated and the lens displays G/S INHIBIT on two lines.  The NG korry has a more orange coloured hue, and displays BELOW G/S P/INHIBIT on two lines.

LEFT:  Captain-side NG compliant korry (click to enlarge).

Further Information

To read more about OEM annunciators, how to wire them, and the main differences between OEM and reproduction units:

OEM Annunciators Replace Reproduction Annunciators in MIP.