8. Warning Speaker
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A. Aural Warning from the computer is audible through the control cabin interphone speakers, located on captain's and first officer's lower auxiliary panels. The speaker provides an aural indication that the GPWC has generated a warning of an unsafe flight path.
9. Operation
_________
A. Functional Description (Fig. 2 and 3)
(1) The GPWS is operational when load control centers P7 and P12 are energized and the CADC, GPWS, LRRA, VOR, GS, landing gear, and inboard trailing edge flaps position circuit breakers are closed.
EFFECTIVITY
AF ALL;LH ALL;SN ALL; CONFIG 1 AT ALL;GN ALL;MD ALL; ATG Page 3 VM ALL Dec 25/87
34-46-00
AIRPLANES INCORPORATING(E2-1) SB 34-2171 Ground Proximity Warning System Simplified Schematic Figure 2 (Sheet 9)
EFFECTIVITY
AF ALL; SN ALL; GN ALL;
CONFIG 1 MD ALL; VM ALL
799 Page 12
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Apr 25/85
.......XA
(2)
Signal inputs to the GPWC consist of radio altitude information from LRRA No. 1, altitude rate information from CADC No. 1 and glide slope deviation information from the VOR/ILS systems. 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, and a high level sensitivity of 1 volt/deviation dot.
(3)
Binary inputs to the GPWC consists of a landing gear position, landing flaps position, 28-volt dc radio altimeter valid, air data computer valid, stall warning/overrotation, ILS truned and 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 position signal is ground potential when the flags are not in landing range, and open when the flaps are in landing range.
(4)
The GPWC processes the input signals to provide warning outputs during the following flight conditions:
(a) Excessive sink rate warning (Mode 1)
1) The barometric sink rate and the 2400-foot radio altitude detector signal to switch the gate on and indicate excessive sink rate.
2) The system provides a minimum warning time of approximately 30 seconds prior to predicted terrain impact at radio altitude between 1180 and 2450 feet. Less warning time is provided below 1180 feet of radio altitude.
(b)
Closure warning (Mode 2)
1) The terrain closure rate detector combines the output of the radio altitude (linearized), flap logic, and the unsafe descent rate to provide a warning as shown in the curve.
(c)
Negative climb rate warning (Mode 3)
1) A warning is provided when the airplane is at a less than 700-foot terrain clearance, landing gear or flaps up in takeoff/landing mode, and a barometric altitude loss is detected. The altitude loss required to activate the GPWS warning varies with the height of the airplane at the time of inadvertent descent occurs. At a climbout altitude of 100 feet, any loss of altitude will activate the warning. At 700 feet, an altitude loss of 70 feet will activate the warning.
2) The flip-flop is set to takeoff/landing mode when the radio altitude is less than 700 feet, with landing gears down and flaps down.
(d) Unsafe terrain clearance warning (Mode 4)
EFFECTIVITY
AF ALL;LH ALL;SN ALL; CONFIG 1 AT ALL;GN ALL;MD ALL; 01 Page 16 VM ALL Apr 25/86
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1) A warning is provided when the airplane is in cruise mode
500 feet with gears up, or in cruise mode with gears down,
flaps up between 200 and 500 feet of radio altitude and a
unsafe descent rate is detected, or in cruise mode at a
radio altitude below 200 feet with gears down and flaps
not in landing range.
2) The flip-flop is set to cruise mode when the radio
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