Re: 757 flight recorder located

From:         ehahn@wren.mitre.org (Ed Hahn)
Organization: The MITRE Corporation, McLean, Va.
Date:         14 Mar 96 17:49:32 
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In article <airliners.1996.348@ohare.Chicago.COM> msb@sq.com (Mark Brader) writes:

<snip about downloading info from FDR via RF link>

> I wonder if it might be feasible, though, to attach something to the
> recorders to make them easier to recover in case of a crash into water.
> I'm thinking of two possibilities.  One is a sonic beacon, to be audible
> from a passing submarine, or a hydrophone on a surface ship; that ought
> to cut the search time quite a bit.  <snip>

Um, that's essentially how things work now.  The FDR and CVR each have
an Underwater Locator Beacon.  They activate via a switch which water
activates due to the mineral (or salt) content.  They ping at about
1/sec at an ultrasonic frequency which has good propogation
characteristics through water, and recovery ships use pinger locators.

Recall that the reason the FDR's and CVR's were located very quickly
after the US Navy brought in locating equipment.  There were other
reasons for delaying the actual recovery of these units (funding, if I
recall).

> The second idea is a float.  Attach to the recorder a sturdy, brightly
> colored balloon and a bottle of a suitable compressed gas.  Again trip
> on a high ambient pressure, being sure to provide enough gas to inflate
> the balloon against that presssure.  This apparatus could be entirely
> mechanical, so power is not an issue.  A drawback is that it might not
> work -- the crash must destroy the plane sufficiently that the recorder
> and balloon can float free.  (I have no idea how firmly the recorders
> are fastened down in normal operation, I must admit.)  But if they don't,
> well, we're no worse off than we would be today.

Both of these boxes are well-bolted to the structure of the aircraft.
The damage necessary to free the CVR would be rather extreme  (i.e.
explosion between the unit and the tray.)  In addition, the presense
of a compressed gas unit in an aircraft would probably be a
significant safety hazard in itself.  (The only compressed gas I'm
aware of inside the fuselage on newer model aircraft are the pilot's
oxygen bottles, and they are treated with great respect.  Passenger
emergency oxygen on more recent aircraft are provided by perchlorate
candles, similar to emergency oxygen systems on submarines.)

Finally, it's probably useful to have the units remain located with the
wreckage of an aircraft, in order to allow recovery of other aircraft
components.

Hope this helps,
ed

--------   Ed Hahn | ehahn@mitre.org | (703) 883-5988   --------
The above comment reflects the opinions of the author, and does not
constitute endorsement or implied warranty by the MITRE Corporation.
Really, I wouldn't kid you about a thing like this.