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 policy for FDR maintenance and record-keeping. In 1997, after a series of accidents that involved problems with extracting data from retrofitted FDRs, the Safety Board issued a safety recommendation (A-97-30) that asked the FAA to publish an AC addressing the certification and maintenance of FDRs.

Safety Recommendation A-91-23 asked the FAA to

{{Smaller|Issue permanent policy and guidance material for the continued airworthiness of digital flight data recorder systems, stating that the make and model of the flight data recorder and the make and model of the flight data acquisition unit, if installed, must be maintained as part of each aircraft's records, as well as at least the following information for each parameter recorded:
 * Location of parameter word (2 through 64 or 128). * Assigned bits (1 through 12).
 * Range (in engineering units when applicable).
 * Sign convention (for example, trailing edge up = +). * Type sensor (for example, synchro or low-level DC). * Accuracy limits (sensor input).
 * FAA requirement (that is, mandatory or not mandatory).
 * Subframe/superframe assignment: Documentation for engineering unit conversion.
 * General equation: Provide A0, A1, A2, and A3 for the equation Y = A0 + A1X + A2X2 + A3X3, where Y = output in engineering units and X = input in decimal or converted counts.
 * Nonlinear parameters: Provide a sufficient number of data samples (engineering units versus recorded decimal counts) to develop a conversion algorithm that will accurately define the full range of the parameter.
 * Discrete parameters: Status (that is, 1 = on, 0 = off).

Safety Recommendation A-91-24 asked the FAA to

{{Smaller|Require operators to maintain current information for each unique digital flight data recorder configuration in its inventory using a single, universally adopted format, such as that described in the standard being developed by Aeronautical Radio, Inc.}} {{rule}}{{Smallrefs}}