Below G/S P-Inhibit Annunciator (korry)

OEM 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 power two incandescent bulbs. This korry came from a 737-500

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.

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 is displayed (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).

Triggering

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

Armed when number 1 glideslope receiver has a valid signal and the aircraft is less than 1000 feet RA.
Excessive deviation below the glideslope.
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.

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.

Glideslope Audio File

The glideslope aural call-out is part of the default sound suite that comes with ProSim737. To ensure you hear the call-out, open the ProSim737 audio program and scroll through the list of available sounds. Ensure you have the glideslope sound ticked (checked). The volume of the call-out can be adjusted in the same place.

ProSim-AR Configuration

The following instructions should provide enough information for you to configure the 318 korry in ProSim-AR. Configuration is done within the config menu of the ProSim737 main module (switches, indicators and audio). The Phidgets library is accessed to determine digital outputs.

config/configuration/combined config/mip/switch/Glideslope (push to inhibit pushed) - Register the output of the korry in ProSim by pressing the annunciator. This will display the output number. Either record the number by clicking the A letter, or manually input the Phidget card information and digital output number (*). Remember to do this for both the Captain and First Officer annunciators.

open Phidgets library - Select the correct Phidget card from the displayed list and open the digital outputs. Find the digital output that corresponds to the glideslope annunciator (work your way through the list of outputs clicking each digital output to you discover the correct entry). When found, click the Turn On command in the call-out box. If you have selected the correct digital output, the glideslope annunciator should now illuminate. Remember the digital output (**).

config/configuration/combined config/mip/indicator/Below GS CP & Below GS F/O - From the menu call-out box select the correct Phidget card number (you may have to scroll down) and select the correct output number (from earlier step marked**).

config/configuration/combined config/audio/glideslope - From the menu call-out box select the correct Phidget card number and then select the correct output number (from earlier step marked **).

OEM 737 Next Generation Captain-side korry

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 illuminated 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.

Further Information

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