2A-31-30: Digital Flight Data Recorder System
1. General Description:
The digital flight data recorder (DFDR) system receives digitized dynamic aircraft
flight environmental data received from the Modular Avionics Units (MAUs). In
addition to the environmental data, the recorder tracks control column, control
wheel forces, and has an accelerometer input. The data is transmitted to the
DFDR and stored in digital memory. The DFDR is located in the tail compartment
aft of the cockpit voice recorder (CVR). See Figure 6.
DFDR operation is limited by integrated relays to record data only when the
aircraft engines are running and the weight-on-wheels (WOW) switches are in the
air mode. A maintenance override switch installed on the monitor and test panel
will bypass the engine fuel pressure and WOW relays to allow maintenance on
the DFDR system while the aircraft is static. The switch is illustrated in Figure 5.
The flight crew may imprint an event stamp on the recorded data in the DFDR to
note a significant instance of flight operations that may warrant subsequent
review, for example, encountering severe air turbulence. The combined DFDR/
CMC EVENT button is located on the cockpit overhead panel above the display
system switching controls as shown in Figure 8.
Like the CVR, the DFDR has an impact switch that closes at 2.5 G to stop the
recording process and preserve recorded data. When the impact switch has been
activated, an adjacent indicator light illuminates signalling that the DFDR has
ceased recording. The impact switch may be reset on the ground. See the
illustration in Figure 7.
An underwater locator device (see Figure 6) is attached to the DFDR to facilitate
recovering the recorder if the aircraft is lost over water.
2. Description of Subsystems, Units and Components:
A. Digital Flight Data Recorder (FDR):
The DFDR records and stores digitized MAU data. The data can be
retrieved to assist in reconstruction of events relevant to an incident. The
DFDR continuously records a minimum of 25 hours of flight data and
retains data in a crash survivable memory unit (CSMU). With electrical
power removed, recorded data is retained for a minimum of two years. The
DFDR is located in the tail compartment aft of the CVR. It is international
orange in color for high visibility and the attached CSMU has two reflective
stripes.
B. DFDR Impact Switch:
The DFDR impact switch, which activates at an acceleration of 2.5 G,
removes power from the DFDR and preserves the data in the CSMU. The
impact switch is mounted in the tail compartment underneath the CVR
mounting shelf. Activation of the impact switch also causes an annunciator
on the switch housing to illuminate until the impact switch is reset. A reset
switch is located on the switch housing.
C. Underwater Locating Beacon (ULB):
An acoustic underwater locating beacon (ULB) is attached to the DFDR.
When activated by contact with water, it transmits an audible signal to aid
underwater location of the aircraft and/or DFDR. The ULB receives power
from a self-contained battery that has an expected life of six years. The
protective casings of the DFDR and CSMU are designed to protect data
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS
2A-31-00
Page 9
July 15/04
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