Honeywell MK VIII, MK XXII manual Fault Isolation Troubleshooting General, Troubleshooting Guide

EGPWS LINE MAINTENANCE MANUAL

3 FAULT ISOLATION (TROUBLESHOOTING)

3.1 GENERAL

The troubleshooting methods provided in this section identify system and sensor or subsystem faults to the lowest level possible. Additional fault isolation in the installation or associated sensors or subsystem should be performed using the aircraft installation and wiring diagrams and other supporting documentation in accordance with established maintenance procedures.

Do not remove or replace the EGPWC until all associated sensors or subsystems and their interfaces have been verified per established maintenance procedures and the fault is isolated to the EGPWC. If the troubleshooting methods determine that the EGPWC is faulty, then the EGPWC should be replaced per Section 6. Route the faulty EGPWC to an authorized repair facility for repair.

3.2 TROUBLESHOOTING GUIDE

In general, if any EGPWS Inoperative status is indicated, the EGPWC front panel LED’s should be checked. The following table shows the recommended maintenance action in response to the front panel LED’s.

EXTERNAL	COMPUTER	COMPUTER
FAULT	OK	FAIL	CORRECTIVE ACTION
OFF	GREEN	OFF	Normal operation.
YELLOW	GREEN	OFF	Troubleshoot external faults using the Level 2 Self-
			Test. DO NOT REMOVE OR REPLACE THE EGPWC
OFF	OFF	OFF	Ensure that the EGPWC is installed in the rack
			correctly and power to the EGPWC is turned on.
OFF	OFF	RED	Record the Level 2 Self-Test, if possible. Remove and
			replace the EGPWC if required.
OFF	GREEN	RED	Record the Level 2 Self-Test, if possible. Remove and
			replace the EGPWC if required.
YELLOW	OFF	OFF	Troubleshoot external faults using the Level 2 Self-
			Test. DO NOT REMOVE OR REPLACE THE EGPWC
YELLOW	OFF	RED	Troubleshoot external faults using the Level 2 Self-
			Test. Remove and replace the EGPWC if required.
YELLOW	GREEN	RED	Record the Level 2 Self-Test, if possible. Troubleshoot
			external faults using the Level 2 Self-Test. Remove
			and replace the EGPWC if required.

A Terrain INOP light rarely implies an external or internal failure of the EGPWC. The Terrain INOP light may turn on if the required accuracy of the position information is not being received from the GPS, IRS, or the FMC. Therefore, if the Terrain INOP light is reported to be on (or was on), perform a Level 2 Self-Test. If no faults are present, verify that position data from the GPS, IRS, or FMC is correct (note: this sentence does not apply to internal GPS engines).

NOTE: The Computer Fail Light will illuminate during some ground test procedures that use the WinVIEWS Software utility, even although no fault exists. The EGPWS Computer Fail Light will extinguish after testing has completed.

The following sections detail the operation of the EGPWS Self-Test and its use in troubleshooting EGPWS faults, when initiated by EGPWS Self-Test switches in the aircraft. Reference is made to a “short cancel” and a “long cancel”. A “short cancel” is defined as depressing the Self-Test switch (either in the cockpit or on the EGPWC front panel) for less than 2 seconds. A “long cancel” is defined as depressing the Self-Test switch (either in the cockpit or on the EGPWC front panel) for more than 2 seconds (but not longer than 59 seconds or a fault is indicated and Self- Test is exited). The affect of these is indicated in each section.

CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO.: 060-4199-180 REV: G SHEET 23 of 68