Saab 340B, Operation Manual, Page: 609 / 670

INSTRUMENTS AND RECORDERS, FLIGHT RECORDER SYSTEM
Description
Aircraft Operations Manual
12/3.1
S1
PAGE 1
Apr 01/15
STANDARD A/C 160 − 250
1. GENERAL
The Flight Recorder system consists of four units:
− The Flight Data Acquisition Unit (FDAU) that col-
lects and arranges the data;
− The Digital Flight Data Recorder (DFDR) that
records the data on a magnetic tape;
− The Flight Recorder panel with monitoring lights;
− The triaxial accelerometer.
The Flight Recorder system becomes powered and
and starts to operate as soon as one engine is run-
ning and one generator on line.
2. MAIN COMPONENTS AND SUBSYSTEMS
2.1 Flight Data Acquisition Unit (FDAU)
The FDAU, installed in the avionics rack, samples
data from various sensors and systems according
to a prearranged program which includes different
sampling rates for various parameters. Parameters
prone to high rate of change consequently have the
highest sampling rate while, for example, switch
positions are sampled with a low rate. Analogue
parameters are converted into digital numbers and
all parameters are formatted into a data stream in
which each data word has its fixed location. The
word can thus be easily found on the recorder tape
and recovered for analysis on ground, for example
transcribed into more conveniently readable form,
altitude in feet etc.
2.2 Digital Flight Data Recorder (DFDR)
This is a recorder with a crashproof tape magazine
installed in the rear compartment. The recorder
uses magnetic tape and is of the continuous type
which means that all data is recorded in a continu-
ous stream. However, the recorder can not hold
more data than that corresponding to approximately
25 flight hours. When the tape is filled up, the oldest
data is therefore automatically erased and new data
entered instead. The tape may therefore be looked
upon as an endless band, holding information from
the last 25 flight hours. To prevent unintentional
blanking of recorded data during ground stops or at
maintenance, a relay controlled by either engine oil
pressure switches off the Flight Recorder when en-
gines are not running. The recorder unit is provided
with an underwater locator beacon, automatically
started when submerged in water. It is battery pow-
ered and transmits an acoustic signal for 30 days.
The recorder has a feature that allows the tape to
be played back on ground for dumping of flight
data.
2.3 Flight Recorder Panel
The panel is provided with caution lights for DFDR
or FDAU failures and also an Event pushbutton to
mark events during aircraft operation.
2.4 Triaxial accelerometer
The accelerometer provides the system with data
for vertical, longitudinal and lateral axis.