(2)
Signal inputs to the GPWC consist of radio altitude information from LRRA No. 1, mach and altitude rate information from central air data computer No. 1. The radio altitude signal is a dc voltage which is a function of airplane height above ground level and is useful to approximately 2500 feet. The barometric rate signal is ac with a scale of 250 mv/1000 fpm altitude change. This rate signal is in phase with the 26-volt ac reference from the CADC during ascent and out-of-phase during descent. The glide slope deviation signal provides a low level input with a sensitivity of 75 mv/deviation dot. The mach signal is a three wire synchro output calibrated from zero degrees for a 0.2 mach indication and increasing to one synchro revolution for a 1.2 mach indication.
(3)
Binary inputs to the GPWC consist of a landing gear and landing flap position signal and 28-volt dc radio altimeter valid, glide slope valid, and air data computer valid signals. The landing gear position signal is open when the landing gear is in any position other than down and locked and ground potential when the landing gear is down and locked. The landing flap position signal is ground potential when the flaps are not in landing range, and open when the flaps are in landing range.
EFFECTIVITY
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(4) The GPWC provides nine different voice messages. With the possibility of more than one warning occurring at the same time, the following priority has been established with the associated modes. The highest priority message is always provided. If a higher priority warning occurs, the message will immediately switch to the higher priority message. If a higher priority warning stops, the high priority message will complete before switching to any lower priority message.
Priority________ Message_______ Mode
1 WHOOP WHOOP PULL UP 1 and 2 2 TERRAIN 2 3 TOO LOW - TERRAIN 4 4 TOO LOW - GEAR 4A 5 TOO LOW - FLAPS 4B 6 MINIMUM 6 7 SINK RATE 1 8 DON'T SINK 3 9 GLIDE SLOPE 5
(5) The GPWC processes the input signals to provide warning outputs during the following flight conditions:
(a) Excessive Sink Rate Warning (Mode 1)
1) The computer provides the pilots with a warning if the airplane exceeds the barometric sink rate with respect to terrain clearance as shown in Fig. 3, Sheet 1. The warning is visual and audible and is continuous while the airplane is within the warning area. The aural warning is SINK RATE, and is repeated every 1.5 seconds.
2) The aural warning changes to PULL UP if the airplane sink rate continuous and penetrated the warning area as shown in Fig. 3, Sheet 1. The PULL UP warning boundary is below the SINK RATE warning boundary.
(b) Closure Warning (Mode 2)
1) With the flaps not in landing configuration (airplane in cruise), the computer will provide the pilots with a warning if the airplane exceeds the terrain closure rates with respect to the terrain clearance shown in Fig. 1, Sheet 2. The GPWS indicator and two cycles of aural WARNING TERRAIN come on. If the airplane remains within the curve boundary, the aural warning will change to PULL UP, repeated every 1.5 seconds. Upon leaving the curve boundary, due to either terrain change or pull up maneuver the aural warning will change to TERRAIN, repeated every
1.5 seconds. The warning will remain on until the barometric altitude has increased by 300 feet. During high speed operation, the upper curve boundary is increased lineraly between 0.35 and 0.45 mach to provide early warning.
EFFECTIVITY
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DC
STALL WARNING COMPUTER (E1-3) X85 GROUND PROXIMITY WARNING COMPUTER (E2-1)
Ground Proximity Warning System Simplified Schematic
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