Flight data recorders

From:         hoel@umiacs.umd.edu (Erik Hoel)
Organization: UMIACS, University of Maryland, College Park, MD 20742
Date:         20 Nov 94 01:59:02 
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Given all the recent downed airliner tragedies, I became curious as to
how the flight data recorders actually work. Basically, how are they able
to record 30 minutes (??) worth of instrument data in such a fashion as to
be able to withstand a terrific impact and fire? 

My uneducated guess is that they "record" the data onto thin metal "tape" 
in a physical manner (i.e., such as scratching). Of course, the basic 
problem here is how to rerecord the tape, etc. during the next flight. 
Perhaps there is a type of magnetic tape that can withstand the heat of a 
fire - this would be a better solution.

Another question - what information is actually recorded?

Finally, is it ever the case that the impact is so severe as to destroy the 
information contained in the black boxes?

In any event, I would enjoy hearing more about flight data recorders (and
cockpit voice recorders) from the experts in this newsgroup.

Signed,

Curious in College Park

(Erik Hoel:hoel@cs.umd.edu)