Re: 757 flight recorder located

From:         msb@sq.com (Mark Brader)
Organization: SoftQuad Inc., Toronto, Canada
Date:         07 Mar 96 02:04:43 
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Robert Ashcroft (rna@gsb-birr.Stanford.EDU) wrote:
> > News item in the newspaper today (Feb 16) said that the flight
> > recorder from the Alas/Birgenair 757 had been located on the seabed...

John Bay (bay@daacdev1.stx.com) writes:
> Would it be possible to make a flight recorder that would transmit all
> its stored data upon request, thereby eliminating the necessity to
> physically recover the box?

This is unlikely to be an issue for a crash on land, so I assume we're
talking about the ocean (or a big lake), as with this particular
crash.  In that case, the same problems would be faced that submarines
have in communicating when submerged.  Water is practically opaque to
radio waves, and while it will transmit sound waves, they get distorted
over long distances.

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.  To activate it in the case of a
crash into water, a pressure-sensitive switch could be used -- to trip
when the ambient pressure reaches, say, 3 atmospheres, indicating that
the device is about 65 feet (20 m) underwater.  But the beacon would need
battery power, and to be heard at a sufficient distance, maybe more power
than it's feasible to provide.

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.

--
Mark Brader          \ "The occasional accidents had been much overemphasized,
msb@sq.com            \  and later investigations ... revealed that nearly 90%
SoftQuad Inc., Toronto \  ... could have been prevented."   --Wiley Post, 1931

My text in this article is in the public domain.