The Role of Flight Recorders

Further regulations were issued in 1947 but were cancelled the following year due to the lack of suitable recorders. It was not until 1958 that the first significant amendment was introduced which require all aircraft over 12,500 pounds operated by air carriers above 25,000ft to record pressure altitude in feet, indicated airspeed in knots, magnetic heading in degrees, vertical acceleration in G’s and elapsed time. A further amendment the following year required the retention of recorded data for 60 days and for the recorder to operate from the beginning of the takeoff roll, during the entire flight and until the end of the landing roll.

1969 saw the introduction of a requirement to record an expanded number of parameters and in 1974 it became mandatory that the recorder be equipped with an underwater locator beacon (ULB).

Finally, in October 1991 the latest regulations went into effect in the US requiring 28 parameter digital FDR’s in all Air Carrier and Charter aircraft, and significantly, FDR’s in GA multi engine turbine aircraft and helicopters with a seating capacity of 10 or more excluding the pilots.

At the same time regulations were introduced requiring Cockpit Voice Recorders (CVR’s) to be hot microphoned on all new Air carrier and Charter aircraft, and again significantly, all GA aircraft with six or more passenger seats requiring two pilots.

Use of FDR’S in Accident Investigation

Increasingly, FDR’s are proving their worth in the investigation of incidents and occurrences. Modern high technology electronic aircraft have the capability to record hundreds of parameters and analysis of recorded data has helped determine what happened, particularly with computer malfunctions in “glass cockpit” aircraft.

In a recent case, the Transportation Safety Board of Canada (TSB) was able to determine precisely what happened when an Air Canada A320 left its assigned altitude after the crew had reportedly pulled the wrong circuit breaker in response to a computer malfunction. Examination of the recorded data showed that the failure was transient, but that the warning of failure had remained latched with the result that the crew failed a “good” computer, however the other computer did not take over operation. When the system was reengaged, the crew failed to notice that the computer had set itself to 100kts, and with auto- thrust restored, the engines were commanded to reduce to flight idle. After discovering the 100kts dialled in by the computer, the crew had further problems with the autothrottle control which did not respond as they expected. Finally, however, they sorted out their problems and the aircraft was returned to it’s assigned level. The point of the story is that without full analysis of all the events, the incident would have been put down to crew error. More importantly perhaps, analysis of the incident helped to highlight the fact that many crews did not have a detailed knowledge of the operation of the throttle system on the A320, Airbus has since corrected minor anomalies in the computer system and Crews have been educated on the exact operation of the throttle system. (However, as one 767 captain was heard to remark, there is a lot to be said for having a throttle system which gives you power when you put the levers forward!)

A320 Accident Bangalore, India

At the request of the Indian Government, the TSB analysed the FDR and CVR readouts for the A320 accident at Bangalore, India. Although there were over two hundred parameters recorded, several which would have been highly desirable were not. Two such parameters, “selected speed” and “selected alti-tude” as chosen by the crew, were not recorded. These parameters would have been extremely valuable in the given circumstances of the accident.

Shortly after the Bangalore investigation, Airbus met with investigators and regulatory bodies associated with A320 operations and reviewed the parameter list to reprioritise requirements. As the recorder was already full, some give and take was necessary, not without objections from some operators who were concerned that their maintenance needs would suffer. However, it was the view of the investigators that flight data must have priority over maintenance, a view that most would support.

Use of FDR’s for Performance Monitoring

Captain John Faulkner, Manager Fight Safety, Qantas reported that Qantas has been using Quick Access recorders for a little over three years to monitor some 2,000 parameters on the 747-400. The data obtained is used to monitor the operating standards of the airline and to identify any undesirable trends that may develop. The data is also used to monitor aircraft systems and performance, engineering problems that may be developing, constraints imposed by other agencies eg ATC, and as an audit that training and route procedures are achieving their objectives.

An interesting development has been the monitoring of piloting exceedences. An example quoted was the discovery that shortly after lift off, aircraft speeds were bleeding back to V2 and sometimes under. Examination of all rotations across the fleet confirmed there was a trend. It was then established that the problem was partly caused by new instrumentation and that pilots were not sufficiently aware of the “raw” correct pitch angles and were tending to over pitch on rotation. The problem was publicised within the airline and quickly resolved.

Flight Data Analysis and Presentation

Both Canada and France have developed sophisticated flight data playback centres in which CVR’s, solid state digital and analog FRD’s, air traffic control tapes and video tapes can be played back for analysis. The concept is for technical experts in the various fields associated with the collection, processing and presentation of the data, to provide all the technical support necessary for the investigators to carry out their task. The French laboratory was designed in close consultation with the Canadian TSB and consists of functional modules directed towards a central meeting room. The modules are the recorder opening work shop, the image processing module, the FDR computer room, the CVR acoustic studio and finally a module handling ATC information.

The investigators are freed from the need to have detailed computer knowledge and can, after consultation amongst themselves call for the information they require. This will be provided to them through the image processing module in the form of video, digitalised computer files, paper printouts or overhead projection. Colour adjustment, Intelligent zooming, scaling or other functions can be provided.

Finally, as an example of the advances made in alds to accident investigation, the latest development, “Reconstruction Animation Graphics Software” provides a video presentation of an aircraft’s fight path and manoeuvres using the information extracted from the FDR. The presentation gives a 3D plus time graphical reconstruction of events. Computer imaging gives a presentation similar to an animated cartoon with a trace behind the aircraft showing it’s flight path. To the right of the screen are displayed the aircraft’s flight instruments showing the actual readings associated with the manoeuvre being performed. Below the screen are linear scales showing control deflections, engine readouts and flaps and undercarriage states.

MrAntoine, Head of the Laboratories, Bureau Enquetes-Acci, France completed his presentation with a video reconstruction of a stall incident involving a wide body jet at Moscow airport. This proved to be a most vivid and explicit demonstration of the worth of this latest development. The aircraft was seen to execute a series of stalls involving over vertical manoeuvres, with the aircraft self recovering each time. It was possible to follow the sequence of events through the flight instruments and to note the control deflections at each attempted recovery. The whole incident took place over a period of five minutes which must have been a nightmare for the passengers!

The Way Ahead

Developments in FDR’s have been almost exponential over the last decade with the latest development being solid state recorders. The introduction of solid state recorders has many advantages for the user.

Firstly for the accident investigator there is better accident survivability of the FDR combined with ease of retrieval of data which is already in digital format for computer analysis.

For the aircraft operator the major factor is low maintenance (fit and forget), with a MTBF of 15,000 to 20,000 hours. In addition this latest development provides a quick access recorder with data easily dumped to a simple data retrieval unit without the need to remove the recorder from the aircraft. This provides maintenance and performance monitoring plus rapid incident evaluation.

Perhaps the proof of the value of solid state recorders lies in the fact that many operators are updating older aircraft with this latest development.

Summary

FDR’s will not directly stop aircraft accidents, but their intelligent use will detect divergent trends In aircraft operation and maintenance which in turn may help to prevent the accident of the future.