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Flight Recorder Report 


James A. Furr (EAL)

The following article, adapted from a paper presented by the author at the 1962-63 Air Safety Forum, is the fourth of the Forum papers to be published by THE AIR LINE PILOT. "Flight Recorder Report" takes on added significance at this time because of the FAA's recent Notice of Proposed Rule Making concerning the installation of cockpit voice recorders. 

The pressing need for information in aircraft accidents, makes it appear to us closely involved, that before the dust settles a hue and cry is raised by press, public and Government for the information contained in the flight recorder. Obviously the initial requirement is to locate the recorder - a feat sometimes similar to the proverbial needle in the haystack. 

Once we have the equipment, the ensuing tedious, time consuming and highly technical job of interpreting the hieroglyphics begins. The main thrust of my effort will be directed toward informing you of the methods and procedures used in accomplishing the readout;
The time and effort involved -
Value of the readout -
Recorder capabilities -
Effects on tape condition from fire, 
immersion, impact, etc. 
In addition to these I will cover the need for improvement as to the amount of information or, Additional Parameters -. For more desirable location in the aircraft and my own interpretation of the Government and industry thinking on flight recorders and the new gadget called Voice, Sound or Cockpit Recorders, depending on your viewpoint. 
The three most used flight recorders imprint information on a metal foil. Two use a steel foil, the other aluminum. There is one recorder in use that uses a magnetic tape. This discussion will deal primarily however with the types using the metal foil. Information is recorded by the use of a stylus, which scribes a mark on the foil in accordance with information it receives from the actuator to which it is coupled. The parameters recorded are altitude, vertical acceleration, airspeed and heading in relation to time. the altitude and A/S styli are actuated by self-contained bellows, similar to those used in A/C instruments. Generally they receive both pitot and static information from a source supplying the First Officer's instruments. Vertical acceleration is obtained in one recorder by having a self-contained weight having a stylus attached and supported by a price of spring steel. Another model uses a remote accelerometer located in the center of gravity of the aircraft, and by means of a transducer the information is electrically transmitted to the recorder and there inscribed. Heading is taken off the fluxgate compass, and is fed to the recorder and there inscribed by the stylus driven by a cam arrangement. 

Time in one model is recorded by a cam arrangement on the other types by exact spacing of perforations along both edges of the foil driving the tape at a constant speed stabilized by 400 cycle A/C. A fixed stylus records a straight reference line at the bottom of the foil. This line is used for basic reference from which a measurement in fractions of an inch is made vertically to the various parameters. When applying these values to an accurate calibration chart, increments of altitude, A/S, "G" forces and heading can be obtained. 

I would like to review, very briefly the FAA TSO C51 dealing with flight data recorders. Recorders are required to operate in a suitable temperature range, a humidity requirement and a vibration requirement. They must emit no objectional radio interference, or no magnetic effect. The recording spped should be no less than 6 inches per hour. The recorder must be able to withstand impact forces of 100 "G"s, sustain a temperature of 1100°C for 30 minutes on type one or 15 minutes on type two, these depending on the location of the recorder. It must be able to withstand 36 hours