A98H0003 - Interim Aviation Safety Recommendations for Flight Recorder Duration and Power Supply

Duration of Cockpit Voice Recorder Information

The CVR installed on SWR 111 employed a continuous-loop magnetic tape of 30 minutes duration. The earliest information on the SWR 111 CVR was recorded approximately 15 minutes before the unusual smell was noted by the crew. Crew conversations and cockpit sounds prior to the beginning of the CVR recording may have provided substantial insight into any initiating or precursor events that led to the accident.

Approximately 38 minutes prior to the unusual smell, Boston Center gave SWR 111 a radio frequency change. During the following 13 minutes Boston Center made repeated attempts to contact SWR 111, without establishing contact. Any cockpit conversations, flight deck noises, or attempted crew transmissions that occurred during this period were subsequently overwritten on the CVR, and therefore could not be assessed.

The 30-minute CVR recording capacity was predicated upon the technology available in the early 1960s; this was the amount of tape that could be crash-protected. The Board is concerned that 30 minutes of recording time is not adequate to capture the initiating events and important background information to many accidents. For example, in accidents involving in-flight fire or progressive structural failure, the initiating events typically develop over a period of time longer than 30 minutes. Longer CVR recording capacity also facilitates the investigation of non-catastrophic occurrences, occurrences in which current 30-minute recordings are often overwritten by the time the aircraft has safely stopped on the ground.

Current technology easily accommodates increased CVR recording capacity. In fact, the majority of newly manufactured solid-state memory CVRs have a two-hour recording capacity, and there is a worldwide industry move towards two-hour CVRs. The European Joint Airworthiness Requirements specify that aircraft first certified after 01 April 1998 be fitted with two-hour CVRs. There is also a proposal to include such a requirement in the Standards and Recommended Practices of the International Civil Aviation Organization (ICAO). The ICAO Flight Recorder Panel, consisting of experts from a number of States, met on 12-20 November 1998, and recommended to ICAO's Air Navigation Commission that aircraft manufactured after 01 January 2003 be fitted with two-hour CVRs.

The TSB is aware that many operators are voluntarily replacing their old technology (tape) data and voice recorders with modern, solid-state recorders. The use of these new recorders not only serves safety but also benefits operators directly, as they avoid the high costs and technical problems associated with maintaining outdated old-technology recorders. Additionally, tape recorders no longer meet the most recent United States Technical Standard Orders (TSO) C123a and TSO C124a crashworthiness standards. This industry trend to solid-state recorders makes it timely to require two-hour CVRs.

A lack of recorded voice and other aural information can inhibit safety investigations and delay or prevent the identification of safety deficiencies. Given the need for longer periods of recorded sound to capture the initiating events of aviation accidents and the availability of two-hour CVRs, the Board believes that such recorders should be mandated by regulatory authorities worldwide. However, it also recognizes that a period of several years may be reasonably required for manufacturers and operators to implement this change. Therefore, for newly manufactured aircraft, the Board recommends that:

As of 01 January 2003, any CVR installed on an aircraft as a condition of that aircraft receiving an original certificate of airworthiness be required to have a recording capacity of at least two hours. (A99-01)

Transport Canada's Response:

Transport Canada fully supports this recommendation and notes that it is similar to an amendment to ICAO Annex 6 proposed by the ICAO Flight Recorder Panel to the Air Navigation Commission. A Notice of Proposed Amendment encompassing this recommendation will be made to the Canadian Aviation Regulatory Advisory Council (CARAC).

Further, the Board believes that, with appropriate lead time, a retrofit program is warranted for aircraft already in service. Therefore the Board recommends that:

As of 01 January 2005, all aircraft that require both an FDR and a CVR be required to be fitted with a CVR having a recording capacity of at least two hours. (A99-02)

Transport Canada's Response:

Transport Canada will introduce an appropriate Notice of Proposed Amendment into the CARAC process. The Department supports this recommendation with the provision that U.S. and Canadian requirements are harmonized.

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