> In a message dated 4/16/98 10:50:52 AM Central Daylight Time, mark@unicorn.com
> writes:
>
> << I've seen a serious proposal for a system which could bring down an
> entire 747 by parachute in a serious inflight emergency (or individual
> pieces if the plane should partially break up in flight). The problem is
> again cost and mass; AFAIR it requires fourteen large parachutes fitted
> to various parts of the plane.
> >>
> I seem to recall some time ago that one of the combat aircraft (?) was fitted
> with a system whereby the entire crew compartment ejected as a whole with
> built in parachutes...what would be the problem in having such a concept for
> commercial passenger aircraft?
The biggest problem with doing exactly that is political: how is it
going to look that the airlines buy that sort of protection for the
crew, but not the passengers?
Please note that the combat aircraft had an ejection mechanism for
the CREW compartment. Not the CARGO compartment.
And, for that matter, the combat aircraft did not have flight
attendants among its crew.
> That is: in the event of a "crash and burn"
> emergency the pilot could eject the passenger compartment.
And here you have changed the protection from the CREW compartment to
the CARGO compartment.
> It then descending
> on it's own automatically deployed chutes. Since said compartment would be
> much lighter than the entire airframe it would possible require less chutes.
Hm... it would lose the wings, wing anchor structure, cockpit, tail
assembly, and part of the undercarriage. Maybe as much as 2/3 of the
unloaded weight of the aircraft. It would also have no fuel tanks...
but it WOULD have PASSENGERS. And it WOULD still have to be
PRESSURIZED.
But there is a more fundamental problem.
Typical loss-of-airframe emergency situation involving a military
aircraft in wartime: the plane took damage from enemy fire while at
altitude. The highly-trained crew is thoroughly strapped in,
five-point harnesses minimum, to seats that are firmly attached to
the ejection assembly and don't adjust. Depending on the severity of
the situation, they can eject immediately or delay (somewhat) to a
more convenient location. If they have to eject immediately, a small
pod wrapped around the seat -- if that much -- ejects with them; the
seat is equipped with oxygen gear equivalent to pressurization, which
the crew is already wearing. And since they are already at altitude,
there is plenty of room for parachutes to deploy, not only cushioning
the fall but also disposing of any forward speed.
Typical loss-of-airframe emergency situation involving a commercial
airliner: the plane rams into the ground. That's how much warning
there is. The untrained passengers are in seats which adjust and are
in uncertain positions; the majority of them, but probably not all,
are wearing two-point safety harnesses (seat belts). Oxygen masks
are available but the passengers have near-zero training and
absolute-zero experience in their use, and they are not attached to
the passengers. If the passenger compartment must be ejected, it is
*huge* compared to the passengers it contains, and will take a very
high g-force acceleration to throw it clear of the impact. Then it
isn't really high enough for chutes to deploy and slow its forward
speed, so its own impact is nearly as bad as the impact of the
airframe.
>
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