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SR 111 Investigation Report

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1.11.2  Recorder Installation Power Requirements

The CVR was powered by the 115 V right emergency AC bus and the FDR was powered by the 115 V AC Bus 3. Both buses are part of the 115 V AC Generator Bus 3 distribution system.

FAR 25.1457 (CVR), FAR 25.1459 (FDR), and the equivalent JARs, require that recorders be installed so that they receive power from the electrical bus that provides the maximum reliability for operation without jeopardizing service to essential services or emergency loads. Transport Canada's Canadian Aviation Regulations Standards Part V – Airworthiness Manual, Chapter 551, Articles 551.100 and 551.101 state that the FDRs and the CVRs shall be installed in accordance with the European Organisation for Civil Aviation Equipment (EUROCAE) documents ED-55 and ED-56A respectively. Additionally, the EUROCAE[49] references suggest that the FDR and the CVR be powered by separate sources.

Initially on the DC-10, the FDR was electrically powered by the 115 V AC Bus 3, and the CVR from 115 V AC Bus 1. However, for JAA certification, the CVR had to be powered by the 115 V right emergency AC bus, which is in turn powered by Generator Bus 3. As a result, both recorders were powered by the same source: Generator Bus 3. The MD-11 emergency checklist dealing with smoke/fumes of unknown origin requires the use of the SMOKE ELEC/AIR selector. This selector is used to cut power to each of the three electrical buses, in turn, to isolate the source of the smoke/fumes. The nature of this troubleshooting procedure requires that the selector remain in each position for an indeterminate amount of time, typically at least a few minutes. When the SMOKE ELEC/AIR selector is placed in the first (3/1 OFF) position, AC Generator Bus 3 is turned off, thereby simultaneously disabling the FDR and the CVR. With both the CVR and the FDR on the same generator bus, a failure of that bus, or the intentional disabling of the bus (e.g., as a result of checklist actions in a smoke situation), will result in both recorders losing power simultaneously.

[49]    The European Organisation for Civil Aviation Equipment prepares minimum performance specifications for airborne electronic equipment; however, these specifications remain as guidelines for consideration until mandated by regulatory authorities.

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Updated: 2003-03-27

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Important Notices