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The Safety Board was unable to validate data from 11 retrofitted sensors on the accident airplane's FDR because Korean Air lacked complete and accurate documentation information for them. Although the data from the retrofitted sensors were not critical in the investigation of this accident, the data might have been important under other accident circumstances. For FDR data to be useful during an accident investigation, accurate documentation that is readily available to investigators after an accident is needed.

After taking delivery of an airplane from a manufacturer, many airlines provide additional data to be recorded on the FDR by retrofitting the airplane with additional sensors or recording additional data from a flight data acquisition unit. Such retrofits are often mandated by the governing CAA. In addition to the flight 801 accident, the Safety Board has investigated several other recent accidents in which airlines were unable to provide accurate and complete information from a retrofitted FDR because the airlines were unable to provide FDR documentation necessary for a complete and thorough readout. Thus, the Safety Board often lacked critical data for a reconstruction of the airplane's motion and the flight crew's performance, which prolonged some investigations.

The Safety Board has long been concerned about inadequate FDR documentation. Since the early 1970s, the Board has made recommendations to improve FDR data verification and documentation. In 1991, concerns about the airworthiness of FDRs resulted in two safety recommendations to the FAA (A-91-23 and -24) aimed at developing a permanent policy for FDR maintenance and record-keeping. Safety Recommendation A-97-30 asked the FAA to publish, by January 1998, a promised AC addressing the installation and maintenance of FDRs.

On October 5, 1999, the FAA issued AC 20-141, "Airworthiness and Operational Approval of Digital Flight Data Recorder Systems." The purpose of the AC is to provide "guidance on design, installation, and continued airworthiness of Digital Flight Data Recorder Systems." Appendix 1 to the AC, "Standard Data Format for Digital Flight Data Recorder Data Stream Format and Correlation Documentation," provides "a standard for the data stream format and correlation documentation that operators must maintain to aid accident investigators in interpreting recorded flight data." The appendix details how to develop a document for each airplane that would provide the detailed information needed by Safety Board investigators to transcribe each parameter recorded by an FDR.