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basis before the recording capacity was reached and data was lost. The cartridge/disk was then
transferred to the readout facility (typically the flight safety department) where each
cartridge/disk was individually handled and replayed. After replay, the cartridges/disks were
stored for a sufficiently long period to allow for any necessary follow-up analysis, then
reformatted and sent to stores for eventual return to an aircraft. There was an obvious cost in
23 PCMCIA: Portable Computer Memory Card International Association.
24 CF: Compact Flash.
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acquiring sufficient cartridges/disks for this cycle and the manpower involved in retrieval and
replay. There was also the opportunity for cartridges/disks to be lost with the loss of valuable
data. The media handling statistics for one airline were:
o international aircraft: 168 (15,270 legs/month)
o average of 124 tapes or disks per day
o domestic aircraft: 70 (11,266 legs/month)
o average 43 disks per day
Wireless technology is now being used to transmit QAR data without the need for manual
handling. This will lower the cost of data recovery and increase the timeliness and availability
of data.
Figure 14: Description of Teledyne Wireless QAR25
25 http://www.teledyne-controls.com/pdf/GroundLink.pdf
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4.2 FDR data recovery
While in-flight telemetry has been used for decades for missile launches and space travel it is
unlikely to replace a fixed onboard FDR (or CVR). The reasons are:
• Cost - all in-flight data transmissions have to be paid for by the operator. While it is
cost-effective to transmit snapshots of important data e.g. ACARS26 it would be
expensive to continuously transmit large amounts of data in-flight.
• Reliability - a satellite link would be needed to transmit data during oceanic cruise.
Would this be reliable if the aircraft was experiencing electrical problems or had
experienced a loss of control?
• Sovereignty issues - transmitted data may be held in a third state and not the state of
occurrence or the state of the operator as defined in ICAO Annex 13. Would this data be
under the control of the investigation team?
Storing data in an onboard recorder is still the cheapest and most reliable storage technique
even allowing for the occasional deep-sea underwater recovery.
Data recovery, from an undamaged solid-state FDR, is performed by connecting a PC to the
FDR and downloading the crash-survivable memory unit contents as shown in Figure 15.
Figure 15: Downloading data from a solid-state FDR
Damaged recorders require specialist recovery techniques that vary according to the FDR
model and type of recording medium.
26 ACARS: Aircraft Communications, Addressing and Reporting System.
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4.3 FDR system documentation
Figure 16 shows the data flow through an FDR system. An essential step in data recovery is the
engineering unit conversion where the raw binary data is mathematically processed to obtain
the relevant engineering unit eg. the raw data recorded for indicated airspeed is converted to
knots. For modern airliners, recording hundreds or thousands of parameters, it is a huge task to
obtain accurate system documentation, develop the parameter conversion equations and
validate the results. Figure 17 shows the documentation for a Boeing 777.
Figure 16: Data acquisition, recording, recovery and analysis
Figure 17: Boeing B777 FDR system documentation
To aid this process, a specification for Flight Recorder Electronic Documentation (FRED) is
being developed with the aim of storing the documentation within the recorder memory itself.
An XML format is being proposed with the documentation being able to be read by a browser.
This would end the situation of investigation agencies struggling to find up-to-date system
documentation in a timely way after an accident.
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5. READOUT EQUIPMENT
The first generation of FDR’s were analogue devices that recorded data by engraving traces on
a metal foil. To readout the data, the foil was placed on a microscope table where distances
could be accurately measured, correction factors applied and the parameter values derived. It
was a laborious process. Figure 18 shows an example of such a microscope table.
Figure 18: Early Australian readout equipment for analogue FDR’s
The first generation of digital FDR’s appeared in the 1970’s and an example of a readout station
is shown in Figure 19. It was capable of producing data listings and plots.
Figure 19: An early UK readout station for digital FDR’s27
27 W.H. Tench (1973), Read-out and analysis of Flight Data Recordings, Accidents Investigation Branch, UK.
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The first flight recorder readout system for commercial aircraft in Australia was acquired in
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