(f)

(g)

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737-300/400/500MAINTENANCE MANUAL
The flight data recorder tape transport is located inside a crash proof container. The container consists of two halves with a steel outer shell and a fire insulation and fiber glass liner. A gasket is used between the two halves. Expanded material lines the belt and wire entry holes. The container is mounted to the front panel/chassis assembly with vibration isolators.The data is sequentially recorded on eight channels. 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.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, an EOT/BOT sensor detects the clear window in the tape and switches both the tape travel direction and to the next recording track.BITE Functions 1) Recording System Controlling circuitry (RSC) accepts inputs
 from BITE (Built-in Test Equipment) and DATA CHECK circuitry, which provide verification of integrity of the system operation and the recorded data.
 2)  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
 3)  BITE also monitors track select, broken tape, record system lock-up (CPU function), invalid data, flight record mode, input data loss, and EOT (End Of Tape)/BOT (Beginning Of Tape) signals from EOT/BOT sensors.
 4)  When a failure is detected, BITE circuitry in flight data recorder sends a maintenance flag discrete signal to the BITE LED on the front panel of flight data recorder and OFF light on the flight data recorder test module.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 3.  Accelerometer (Fig. 1)
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 A.  The accelerometer is a self-contained sealed unit mounted on the aft side of the forward wall of the right wheel well at station 663, RBL50, WL188 and is accessible through the wheel well. The accelerometer sensitive axis is oriented to detect vertical acceleration forces with a range of minus 3 to plus 6 g's. The unit supplies the flight data recorder with a 400-Hz amplitude modulated signal which is a function of vertical acceleration of the airplane. The flight data recorder provides a 26-volt, 400-Hz ac excitation voltage to the accelerometer.
 4.  Underwater Locator Beacon (ULB) (Fig. 1)
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 A.  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.
 5.  Flight Recorder Test Module (Fig. 2)
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 A.  The test module, part of the FLIGHT RECORDER AND MACH AIRSPEED WARNING TEST MODULE, contains a TEST NORMAL switch and an OFF light.
 B.  The push-to-test OFF light, when illuminated, provides indication that the flight data recorder is inoperative. A ground for the light is completed through a de-energized power relay in the flight data recorder when flight data recorder power is not available, or when ground is completed by a 15-second time delay circuit if the tape in the flight data recorder is broken or fouled.
 C.  A transistorized auto-on-off circuit and relay provide 115 volts ac power to the flight data recorder. The transistor circuit is normally conducting when ground power is on the airplane and the airplane engines are not running. The relay is energized and power is not provided to the flight data recorder. The relay will become de-energized thus providing power to the flight data recorder, in any one of three ways. Starting either one of the airplane engines causes an engine oil pressure switch to close thus grounding the transistor and causing the relay to open. If the airplane is airborne and all engines should be shut down, a ground is provided through the ground sensing relay (AIR/GND), keeping the transistor circuit grounded and thus the flight data recorder still operating. A test switch on the test module may be used to operate the flight data recorder during ground maintenance checkout.
　
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