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The Enhanced Ground Proximity Warning Computer (EGPWC)

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Flight deck audio systems (speaker and interphone)

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Alert lamps and/or EFIS or EICAS displays (for alert and system status messages)

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EFIS Navigation Display (ND), Multi-Function Display (MFD), or Weather Radar Indicator for display of terrain

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Switching relay(s) when required for switching display inputs from weather display to terrain display

2.1.1 ENHANCED GROUND PROXIMITY WARNING COMPUTER (EGPWC)
All EGPWS functions are processed by a single Line Replaceable Unit (LRU) called the Enhanced Ground Proximity Warning Computer (EGPWC).
The MK V and MK VII EGPWC are digitally controlled computers housed in a 2 MCU ARINC 600-6 form factor chassis intended for Air Transport type aircraft.  Installation configuration is defined by program pin strapping in the aircraft.
The MK VI and MK VIII EGPWC are digitally controlled computers housed in a non-ARINC form factor chassis intended for Business and General Aviation and Regional Turboprop type aircraft.  These models have fewer interface and functional options.  The installation configuration is defined in a programmed Configuration Module installed in the aircraft.
The EGPWC receives information in AC, DC, discrete, and synchro analog formats, and RS-232, RS-422, ARINC 429 or ARINC 575 digital formats.  Discrete signals can be either ground or +28V discretes.  The EGPWC provides discrete, audio and ARINC 429 outputs for alerts and system status, and video (ARINC 453/708) for terrain display. The EGPWC is rack mounted and does not require any forced air cooling when operated within the normal operating temperature range given in the Table 1.

2.2 OPERATION
2.2.1 MODE 1 - EXCESSIVE DESCENT RATE
Mode 1 provides audio and visual alerts for excessive descent rates into terrain.  When the EGPWS caution alert
envelope is penetrated, the message “SINKRATE” is enunciated and EGPWS alert lights illuminate.  Continuing the excessive descent rate into the EGPWS warning alert envelope results in a “PULL-UP” enunciation and EGPWS alert lights illuminated.  Mode 1 is desensitized to eliminate unwanted (nuisance) alerts when the EGPWS determines that the aircraft is above a Glideslope beam.  In some applications, Mode 1 is also desensitized when Steep Approach or Flap Override is active.

2.2.2 MODE 2A/2B - TERRAIN CLOSURE RATE
Mode 2 provides audio and visual alerts for dangerously high terrain closure rates.  Two sub-modes, referred to as Mode 2A and 2B, are defined.  Mode 2A is active when flaps are not in the landing position and the aircraft is not on an ILS approach within ± 2 dots of glideslope center.  Mode 2B is active when the flaps are in the landing position or while on an ILS approach within ± 2 dots of glideslope deviation.  When the caution alert envelope is penetrated, the message “TERRAIN, TERRAIN” is enunciated and EGPWS alert lights illuminate.  Continuing the high terrain closure rate into the warning alert envelope results in a “PULL-UP” enunciation and EGPWS alert lights illuminated.
　
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