EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. BEJ 101-999 ú

 31-24-01
 ú ú 04A Page 18 ú Mar 12/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (3)  
The data is sequentially recorded on eight channels. The read/write channels are operated by the track select circuit and the tape transport by the microprocessor. During recording, the tape moves two steps forward and one step back. The tape speed stabilizes on the initial step. Recording takes place on the second step which is followed by a back stroke for verification. The data recorded on the preceding second forward step is read for playback and verification during the current first forward step.

 (4)  
The tape passes through the erase head first. Consequently, that portion of the tape is erased before reaching the write head where the new data is recorded. Seperate erase heads and write heads are used for opposite directions of tape travel. At the end of the tape, an EOT/BOT sensor detects the clear window in the tape and switches both the tape travel direction and the recording track.

 D. BITE Functions
 (1)  
The BITE (Built-In Test Equipment) monitors DFDR functions while providing status reports. The status reports are generated in two ways:

 (a)  
Directly by hardware, resulting in the DFDR FAIL light on FDAU illuminating.

 (b)  
Indirectly by providing outputs used by the software which controls the DFDR light and writes status on tape.

 (2)  
The following functions are monitored by BITE:

 (a)  
Power supply functions

 (b)  
Write data presence

 (c)  
Read data presence

 (d)  
Track change (the fault is latched until power is reset)

 (e)  
System clock

 (3)  
When a failure is detected, BITE circuitry in DFDR sends a maintenance flag discrete signal to the DFDR FAIL light on the FDAU. Depending on the type of fault there could be a delay of 0 to 32 seconds before the DFDR FAIL light comes on.

 E. Control
 (1)  
To operate the flight recorder, close Flight Recorder AC, Flight Recorder DC and Position Sensors circuit breakers on P18 circuit breaker panel and place the TEST NORMAL switch in the TEST position.

 (2)  
During normal operation, the flight recorder TEST NORMAL switch is kept in the NORMAL position and the flight recorder is turned on by having either engine running or the ground sensing relay in the AIR position.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. BEJ 101-999 ú

 31-24-01
 ú ú 05A Page 19 ú Mar 12/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 FLIGHT DATA RECORDER SYSTEM - TROUBLE SHOOTING
______________________________________________
 1.  General_______
 A.  The following trouble shooting procedures are based on performing the system operational test and are presented in tree-type format to aid in rapid fault isolation.
 B.  When a test step does not check out, find the box containing the trouble symptom and perform the stated action. Continue to follow a single line by analyzing the results of each test step until the required corrective action is determined. Perform the specified corrective action, then repeat the step at which the failure was encountered and complete the test to check out the system.
 C.  All trouble shooting procedures are based on the assumption that wiring is OK and that electrical power is available. If the corrective action in the procedure does not correct the problem, check wiring using the wiring diagram.
 D.  The flight recorder accepts and records data from other systems in the airplane. Because the flight recorder functions depend on inputs from other systems, these systems should be operationally tested before assuming that an incorrect recording is the result of a defective flight recorder.
 E.  A defect in the acceleration recording system cannot be isolated to either the accelerometer or the flight recorder unit without using an accelerometer simulator. Failure in the flight recorder unit is more probable, and should be replaced first or the two units should be replaced together.
　
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