(6)  
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. Separate erase heads and write heads are used for opposite directions of tape travel. At the end of the tape, the EOT/BOT sensor detects the clear window in the tape and switches both the tape travel direction and to the next recording track.

(7)  
The BITE data processing. Data samples of the same segment are taken at the time the data is received (transmitted to the write head) and when data is played back from the tape. These data samples are compared to verify the following functions.

(a)  
Write driver and write head current

(b) 
 Tape motion

(c) 
 Read/write circuits

(d)  
Generated power supply voltages

(e)  
Playback amplifiers

(8)  
The BITE also monitors EOT/BOT sensors operation, track select, CPU, and data validity.

(9)  
When a failure is detected, fault gate output is a logic 1 which sends a maintenance flag discrete signal to the BITE LED on the UFDR front panel and the OFF light on the flight recorder panel.

5C8 
Jun 20/88  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  31-24-0 Page 5 

Flight Data Recorder System Block Diagram  5C9 
31-24-0  Figure 2  Jun 20/88 
Page 6 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

B.  Power Distribution and Control (Fig. 2)
(1)  
The UFDR receives 115 volts ac power from the FLIGHT RECORDER AC circuit breakers on the P18-2 panel. Power is supplied automatically by the AIR/GND relay thru the control panel when the airplane is in flight. When the airplane is on the ground, power is automatically supplied through the left or right flight recorder control relay when one of the engines is running.

(2)  
Power is manually supplied through the FLIGHT RECORDER CONTROL PANEL TEST-NORMAL switch when set to TEST.

C.  Underwater Locator Beacon (Fig. 1)
(1)  The underwater locator beacon is a battery operated unit that transmits pulses when immersed in water. The ULB has a detection range of 2,000 to 4,000 yards and an operating life of approximately 30 days.
5E1 
Jun 20/84  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  31-24-0 Page 7 

FLIGHT RECORDER SYSTEM - TROUBLE SHOOTING
EFFECTIVITY
Airplanes with Sundstrand Universal Flight Data Recorder (UFDR)
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 are dependent upon inputs from the compass system and the air data computer, these systems should be operationally tested before assuming that an incorrect heading, altitude or airspeed recording is the result of a defective flight recorder.
E.  A defect in the acceleration recording servosystem 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.
2.  Prepare for Trouble Shooting
A.  Before starting the trouble shooting procedure, ensure that operating power is available, that the FLIGHT RECORDER AC and DC circuit breakers on panel P18 are closed, and that data inputs are operating. Check panel lights operation.
5C8
Feb 20/85 31-24-0 Page 101

5C8 
31-24-0 Page 102  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Feb 20/85 

DIGITAL FLIGHT DATA RECORDER - MAINTENANCE PRACTICES
EFFECTIVITY
Airplanes with Digital Flight Data Recorder
1. General
A.  The following paragraphs include procedures for reading data from the DFDR using a copy recorder. The copy tape is used for data analysis off the airplane without having to remove the DFDR or its tape reel from the airplane.
　
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