Air Transport World

Scrutiny in the sky.(flight recorders assume a new role, that of in-flight performance monitors)

Flight recorders, one used only in accident probes, assume a new role: in-flight performance monitors.

When accident investigators reach the site of a major plane crash, one of their first objectives is to locate two items that all large commercial aircraft carry: The recorders that the popular press insists on referring to as "black boxes," despite their orange paint. One recorder will tell investigators the sounds in the cockpit prior to impact. The other will reveal numerous details of the flight, such as altitude, airspeed, vertical acceleration and heading.

Since catastrophic crashes mercifully are rare, most recorders will absorb thousands of hours of data that never reach the hands of accident investigators. Could other purposes be found for this data? Are the details of flights that did not end in tragedy of use to anyone? They are of great use to

flight departments at SAS, British Airways, Swissair and about 17 other carriers. Each has instituted a program of flight-data analysis. Approximately 12 other airlines are developing such programs.

The purpose of flight-data analysis, as outlined to ATW by National Transportation Safety Board member John Lauber, is to identify operational problems that could lead to unsafe conditions and to correct those problems "before we have a reportable accident or incident."

The analysis does not include sound recordings from the cockpit. In the interest of privacy, audio tape in the cockpit voice recorder (CVR) is rerecorded in a continuous loop, so that at any moment, only the most recent 30 min. of conversation are preserved.

Federal regulations require installation of both a CVR and a flight-data recorder (FDR) on large transport-category aircraft. Customarily, the recorders are housed in containers able to withstand the fire, heat and impact forces of a crash. The regulations also specify the items to be recorded by the FDR-as few as 11 parameters for ones with older technology, up to 32 for the newest. Among these are autopilot status, landing-gear-selector position and flap angle.

When an airline undertakes a data analysis program, though, it can study a lot more than just the federally mandated parameters. Thanks to the advent of digital technology, huge volumes of data can be recorded and accessed. For each moment of the flight, the system can report on sensor findings throughout the aircraft, instrument readings, switch and control positions and much more. The device that collects all this data is the digital flight data acquisition unit (DFDAU).

Originally, flight-data recorders were analog devices, recording five or six parameters on metal foil. These were succeeded by digital units recording on magnetic tape and the transition now is under way to solid-state digital recording. The crash-protected digital flight-data recorder (DFDR) can store much of the data coming from the DFDAU but the Air Line Pilots Association (ALPA), among others, recommends that the accident investigation and data analysis functions be kept separate. …

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