(6)
Decision Height Warning (Mode 6) (Not Used)
(7)
Windshear (Mode 7)
(a)
The windshear comparator receives data inputs from the ARINC 429 receiver, in addition to flap position information. Using an algorithm which provides different gain and threshold levels for takeoff and approach modes, and which also provides altitude-dependant gain levels, the windshear comparator computes both vertical and horizontal windshear components.
(b)
The vertical windshear component is computed from data from the stall warning computer (vane AOA), the digital air data computer (true airspeed), and the IRS (body pitch rate). These data are combined with inertial vertical speed, pitch attitude, and roll attitude in order to determine the total vertical component of windshear.
(c)
Horizontal windshear is computed by utilizing DADC true airspeed and flight path acceleration from the IRS.
(d)
The audio message for a windshear condition consists of one cycle of the siren audio (250 and 950 Hz) followed by the distinct word WINDSHEAR.
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737-300/400/500MAINTENANCE MANUAL
(e) When the GPWC is in a windshear alert mode, all other GPWS modes are inhibited.
F. System self-test may be initiated by pressing the SYS TEST switch on the GPWS control module. Two self-tests are available, a confidence test and a full vocabulary test. The confidence test may be initiated either on the ground or in the air (inhibited between lift off and 1000 feet radio altitude) to give the pilots an indication of system operation. The full vocabulary test, which may be initiated only on the ground, is used as an operational test of the system.
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GROUND PROXIMITY WARNING SYSTEM - TROUBLE SHOOTING
__________________________________________________
1. General
_______
A. The trouble shooting has BITE procedures to examine the status of the system.
B. The present status procedure gives a front panel readout of the present status of the system.
C. The flight history procedure gives a front panel readout of the functional status of the system during the last ten flight segments.
D. If a failure shows on the GPWC front panel, refer to the failure code chart (Fig. 101) for an explanation and possible cause.
E. Do the specified procedure to correct the failure and do the BITE procedure again.
F. To cancel the INOP light on the ground, you must correct all failures and do a Flight History BITE.
G. The GPWC INOP lamp has two general modes of operation; IN AIR, and ON GROUND. Each mode monitors different inputs. If the INOP light comes on in the air, the fault is critical to GPWS operation. For less critical flight failures, the INOP light will not come on until the airplane is on the ground. The INOP lamp goes on when failures occur (such as data input failures, invalid program pin conditions, or GPWC hardware or software failures). Failure messages can be identified through the PRESENT STATUS or FLIGHT HISTORY displays on the front panel of the GPWC.
H. The procedures that follow think that all the wiring is OK.
I. If the corrective action does not correct the failure, use the appropriate wiring diagram to make sure all wiring and connections are correct.
2. Prepare for Trouble-Shooting
____________________________
A. Make sure that the following circuit breakers are closed:
NOTE: If a circuit breaker cannot be (or is not) closed, a failure
____
indication will be given for the related system.
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