Newsgroups: comp.risks
X-issue: 5.76
Date: Thu, 10 Dec 87 13:11:29 EST
From: mnetor!utzoo!henry@uunet.UU.NET
To: RISKS@kl.sri.com
Subject: Re: F4 in 'Nam (Reversed signal polarity causing accidents)

> ...the low-tech means that the pilots developed to deal with the problem...
> was to wire a pair of bayonets to the "rails" on either side of the ejection
> seat so that the points projected above the pilot's head.

There are ejection-seat systems nowadays, in fact, that rely on such "canopy
breakers" rather than using a canopy-ejection system.  This does depend on
having a relatively thin canopy; it wouldn't work on the thick one-piece
canopies used on most new US fighters.  But it's certainly simpler and more
reliable than automatic canopy ejection.

Mind you, there is a negative side to having a relatively thin canopy.  There
was a recent accident in Britain, not yet explained in detail, which *might*
have been due to the parachute-deployment system of an ejection seat firing
*through* the canopy by accident (i.e. not as part of an ejection) and pulling
the pilot out of the plane after it.  The plane (a Harrier) unfortunately
kept on flying and eventually ran out of fuel over deep ocean.  Recovering
it will be difficult, but may be tried because more information is badly
needed.

(In case you're wondering why a parachute-deployment system should operate
so violently:  in an ejection at low altitude, getting the parachute out and
inflated *immediately* is very important.)

Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,decvax,pyramid}!utzoo!henry

Newsgroups: comp.risks
X-issue: 6.79
Date: Fri, 6 May 88 15:49:10 EDT
From: mnetor!utzoo!henry@uunet.UU.NET
Subject: Harrier ejection-seat accident

A while ago I mentioned the incident in which a Harrier pilot was apparently
pulled out of his aircraft after the parachute-deployment system on his
ejection seat fired through the canopy.  Flight International just printed
a summary of the final report on the accident.

The problem does indeed appear to have been an accidental firing of the
parachute-deployment system, which is powerful enough to punch its way
through the canopy.  The question is why it fired.  The Harrier flew west
on autopilot until it ran out of fuel, and went down in deep ocean; the
wreckage has not been located despite an extensive search.  (The general
nature of the accident is known because air traffic control, after being
unable to raise the pilot, had another aircraft take a look.)

The inquiry came up with three hypotheses.  In the absence of wreckage,
there is no way to be sure of the answer.  However, two of the hypotheses
require multiple errors and/or multiple failures.  The third is considered
most plausible:  if the seat was lowered, and there was a foreign object
underneath it in just the right place, a connecting linkage on the seat's
underside could have been bent enough to fire the deployment system.  The
Harrier cockpit equipment includes a utility light on a coiled cable; it
is strong enough and large enough to have done the trick, and could have
ended up in the right place if it fell off its bracket.  Also, there is
reason to suspect that the pilot may have lowered the seat at about the
right time:  he was to perform some tests that required a clear view of
the instrument panel, and he was flying into the setting sun, so once he
was flying safely on autopilot he might well have lowered the seat for
a better view of the panel.

Martin-Baker, manufacturers of the ejection seat (with a generally very high
reputation for quality products), are adding a guard over the linkage.  (I'm a
bit surprised that this wasn't done in the original design; somebody assumed
that the cockpit was a controlled environment in which such things couldn't
happen.)  The utility lights have been removed from the Harriers until this is
done.

Henry Spencer @ U of Toronto Zoology   {ihnp4,decvax,uunet!mnetor}!utzoo!henry

Subject: Re: Ejection Seat UL
From: shafer@ferhino.dfrc.nasa.gov (Mary Shafer)
Date: Aug 08 1996
Newsgroups: rec.aviation.military

On 7 Aug 1996 17:14:19 GMT, paul@wit387304.student.utwente.nl (Paul
Boven) said:

P> In article <baldwinDvrtA5.9Dy@netcom.com>, baldwin@netcom.com (J.D.
P> Baldwin) writes:

> Ejection seats are of wide general interest--people just think they're
> *cool*, I guess--so there was once a bit of UL content here, but the
> rest of the discussion belongs in rec.aviation.military.  So ordered.

P> Cool? Perhaps, though I'd rather not use one: one of the ejectees
P> was more than an inch shorter when measured after they picked him
P> up.

This may not be entirely due to the e-seat and it may well be only
temporary.  I'm enough shorter by the end of the workday that I have
to readjust my rear-view mirror; it's claimed that the average adult
loses as much as a half inch of height during the day, due to the
spinal disks compressing.  The effect is small in young people,
increasing as one ages.  However, the disks fluff up during the night,
once lying down removes the g load.

So I'd like to hear how much shorter the ejectee was the next morning,
after a good night's sleep.
--
Mary Shafer               NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer     Of course I don't speak for NASA 
shafer@ferhino.dfrc.nasa.gov                               DoD #362 KotFR   
URL http://www.dfrc.nasa.gov/People/Shafer/mary.html
For personal messages, please use shafer@ursa-major.spdcc.com