Letters to the Editor

Subject: CVR/FDR Backup Power
From: Gary Watson watsong@home.com

I've been installing (designing interfaces, fabricating harness and installing the racks etc.) and maintaining CVRs and FDRs since 1970. I agree totally with the Editor of AirlineSafety.Com, regarding the folly of using a backup battery.

In an electrical failure, such as possibly happened on SR 111, there would be nothing to record on the FDR or from the mic audio channels with the possible exception of the area mic. And, if the wiring had burned through, it too would have been unserviceable.

In the other 99.9% of crashes, the chance that the recorders would continue to run after the crash on their own batteries, is significant in that it could erase all existing information. The recorders run on a continuous write/erase cycle. Thirty minutes for the older tape mechanism machines, two hours for the new solid state CVRs and usually 25 hours for the FDRs.

I have witnessed a great deal of testing and improvements on these devices, since 1970. The comments about lack of proper design are groundless. [See Flight Recorders Need Battery Back-Ups]

The vast majority of airline units are 115 VAC powered. Normally, only the General Aviation units run on 28VDC.

[Mr. Watson has 35 years in the avionics maintenance business as a bench technician, aircraft installer, aircraft installation designer and is a Canadian Transport Canada certified Aircraft Maintenance Engineer with licenses for both avionics and mechanical -- Ed. ]

December, 1998

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