Aviation Investigation Report A98H0003
1.11.4 Lack of CVR Information
The CVR in the occurrence aircraft had a 30-minute recording capacity; this met the existing regulatory requirements. The requirements were predicated upon the technology available in the early 1960s, and 30 minutes represented the amount of recording tape that could reasonably be crash protected. Current technology easily accommodates increased CVR recording capacity. The majority of newly manufactured, solid-state memory CVRs have a two-hour recording capacity; however, regulations pertaining to HB-IWF at the time of the accident did not require more than the 30-minute CVR recording capacity.
The earliest information on the SR 111 CVR was recorded approximately 17 minutes before the unusual smell was detected by the pilots. Conversations and cockpit sounds prior to the beginning of the CVR recording would have been useful in looking for potential initiating or precursor events that led to the in-flight fire.
Aircraft electrical power to the SR 111 flight recorders was interrupted at about 10 000 feet, which resulted in the FDR and the CVR recording stoppage. The aircraft continued to fly for about 5.5 minutes with no information being recorded.
Modern, maintenance-free, independent power sources and new-technology CVRs make it feasible to provide independent CVR and CAM power for at least several minutes. This would allow the continued recording of the acoustic environment of the cockpit, including cockpit conversations and ambient noises, in the event of the loss of aircraft power sources.
Current battery technology would not provide sufficient independent power to allow for the same option for FDR information. The multiple sensors and wiring that feed information to the DFDAU require aircraft power.
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