Re: Swissair MD-11 (SR 111, JFK-GVA) crash off Nova Scotia

Date:         05 Oct 98 00:27:06 
From:         ehahn@mitre.org (Edward Hahn)
Organization: The MITRE Corporation
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In article <airliners.1998.1463@ohare.Chicago.COM>, "S.L." <look@the.sig> wrote:
>Pete Mellor wrote:
>>(The CVR is still to be located, although signals from
>>it have been detected by sonar.)
>
>Do CVR's have acoustic beacons or pingers? I assume they have RF
>beacons, but I didn't know they had pingers.

They do have ultrasonic beacons, but do *not* have RF beacons.

>> Unfortunately, the DFDR was found to have stopped recording at
>> the point at which the aircraft descended below 10,000 feet,
>> i.e., it does not cover the last 6 minutes of the flight, during
>> which the behaviour of the plane is the most mysterious!
>> Investigators speculate that this is due to a total loss of
>> power at that time.
>
>Do DFDR's and CVR's not have internal backup batteries to continue
>powering the recorders for a while after a power failure? Lithium cells
>with service lives of 10 years or more are common as dirt (in personal
>computers and other electronic systems) now, so this shouldn't pose a
>huge maintenance problem

Even if there was internal battery backup for these systems, it would
be of limited use if none of the systems they were hooked up to had
lost power - no input source data would be transmitted to the Flight
Data Acquisition Unit (FDAU) or the FDR.

It should be noted that the aircraft does have a battery bus for
essential systems, and that the FDAU, FDR and CVR are part of these
systems.  For the FDAU, FDR and CVR to have lost power would imply
that the battery bus itself was damaged.  Without an understanding of
exactly where and how much wiring was damaged, it is impossible to
determine one way or another whether an internal battery would have
been of any use.

ed

>>>>  Ed Hahn    |    ehahn@mitre.org    |    (703) 883-5988  <<<<
The above statement is the opinion of the author.  No endorsement
or warranty by the MITRE Corporation is expressed or implied.
Really, I wouldn't kid you about a thing like this.