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 consider circadian rhythms and human sleep and rest requirements. Seek Congressional authority, if necessary, for the modal administrations to establish these regulations.

Safety Recommendation A-99-45 asked the FAA to

Establish within 2 years scientifically based hours-of-service regulations that set limits on hours of service, provide predictable work and rest schedules, and consider circadian rhythms and human sleep and rest requirements.

On July 15, 1999, the FAA indicated that it agreed with the intent of Safety Recommendation A-99-45 and stated that, on December 11, 1998, it had issued NPRM 95-18, which proposed amending existing regulations to establish one set of duty period limitations, flight time limitations, and rest requirements for flight crewmembers engaged in air transportation. The FAA stated that the NPRM considered scientific data from studies conducted by NASA relating to flight crewmember duty periods, flight times, and rest and that Safety Recommendation A-99-45 would be included in this rulemaking project. The FAA further indicated that its Aviation Rulemaking Advisory Committee was tasked to review reserve issues related to the NPRM but was unable to agree on a recommendation. The FAA indicated that it was conducting a risk assessment to determine the probability of preventing future incidents related to fatigue and did not know when a supplemental NPRM would be issued. However, the FAA stated that, in the interim, it published a notice on June 15, 1999, indicating its intent to enforce the regulations concerning flight time limitations and rest requirements. At an October 7, 1999, meeting with the Safety Board's Chairman, the FAA Administrator indicated that a final rule would not be issued within the next 2 years.

A digital flight data recorder (DFDR) records values for parameters related to the operation of an airplane (for example, altitude, airspeed, and heading). The values are recorded in a serial binary digital data stream that must be converted either to engineering units or discrete states. The arrangement of the recorded values often varies among DFDR systems; consequently, accurate conversion of the recorded values to their corresponding engineering units or discrete states can be accomplished only when the configuration of the data has been thoroughly documented.

1.18.7.1 Previous Safety Board Recommendations on Flight Data Recorder Parameter Verification and Documentation

In the early 1970s, the Safety Board began issuing safety recommendations to improve FDR parameter verification and documentation. In 1991, the Safety Board issued two safety recommendations (A-91-23 and -24) to the FAA for developing a permanent