4.  Accelerometer
A.  The accelerometer is a self-contained sealed unit mounted on the aft side of the forward wall of the left wheel well and is accessible through the wheel well. The accelerometer sensitive axis is oriented to detect vertical acceleration forces within a range of minus 4.3 to plus 6.3G. The unit supplies the recorder with a 400-Hz amplitude modulated signal, which is a function of vertical acceleration of the airplane. A 26-volt, 400-Hz ac excitation voltage is provided to the accelerometer from the flight recorder.
5.  Flight Recorder
A.  The flight recorder provides a digitally recorded tape file of the previous 25 hours of airplane flight (normally engine start to engine shutdown). The unit is a long; half ATR box painted international orange with black stripes. The tape transport mechanism in the unit is crash and fire protected. The unit records the required parameters or can be interfaced with a flight data acquisition unit to provide expanded parameter recording of required plus optional signals. The unit contains plug-in circuit cards, which configure the various signals for recording.
B.  The signal format for the recorder is shown in figure 2. The recording rate is 10 words per second. Nine of these words have 12 bits in Harvard biphase code and the tenth word is blank. In order to reduce the bits recorded, each 4 binary data bits are converted into a 5-bit group termed group code recording. This reduces the bits per second recording rate, which in turn permits the slow tape speed and 25 hour data retention while maintaining system accuracy.
6.  Operation (Figure 3)
A.  System operation begins automatically when 115 vac is applied. The trip and date encoder is powered with the recorder and initiates the transmission of the selected codes. The interfacing signals are 3-wire synchro, two-wire analog or discretes.
5C9 
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ARINC 542 Data Format  5C9 
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H31597
5C9 Flight Recorder Block DiagramFeb 20/84 Figure 3 31-24-03 Page 7/8BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

B.  The synchro signals from altitude, airspeed and heading are multiplexed into sine cosine functions in the analog input multiplex card, then converted into digital words in the analog/digital converter card. The signal is provided on the digital bus to the data control interface card.
C.  The vertical accelerometer phase and acceleration relationship are converted into digital words in an analog/digital converter. This data is provided on the digital bus by sync data from the interface card.
D.  The digital data is level shifted and synchronized with discrete data in the interface card and the data bus signal is transmitted to the computer processor card. The CPU card contains the master clock and programmable read-only memory. The CPU provides data and control signals to other devices. CPU data is provided to write amplifier and write head for recording and the read amplifier provides signals back to the CPU and for an external test set. The data is verified within the CPU and status information is sent to the status monitor interface card.
E.  The status monitor interface card provides the monitor function of overall recorder operation. Continuous BITE is performed by this card to verify proper recorder operation. Fault detection operates the monitor status relay, which will illuminate the fault light on the trip and date encoder panel.
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FLIGHT RECORDER SYSTEM - TROUBLE SHOOTING
EFFECTIVITY
Airplanes With Fairchild Digital Flight Recorder (DFR)
1. General
A.  The following trouble shooting procedures are based on performance of 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.
　
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