Punctured pressure cabin.

On Wed, 31 Dec 2003 23:06:55 +0000, "M. J. Powell"
wrote:


There has been a bit of a furore over here concerning the new US
requirement to airlines to supply air marshals when requested. The
concern is mainly over the possible puncture of a pressure cabin.
What do readers think is the result of decompression via a bullet hole?

A little more noise in the cabin, at least near the hole.

Mary

--
Mary Shafer Retired aerospace research engineer

When you consider the source of the air for pressurization, LP/HP air
bled from the engines' compressors, and note that just one engine or,
on most transports, the APU as a last resort, can supply enough air
for normal operation of the pressurization system, it becomes obvious
several bullet holes will not materially affect cabin altitude. Note
also that there is constant flow through the pressurization/dump
valves; they will normally never be fully closed. In sum, the valves'
normal open area could be compared to the aggregate area of the bullet
holes so that when the p/d valves do fully close trying to maintain
pressure one could calculate the number of bullet holes they could
compensate for. A nice experiment waiting to be accomplished. BTW keep
your seat belt fastened and carry a nice sharp 6H drafting pencil in
your kit.
Walt BJ

"M. J. Powell" wrote:

What do readers think is the result of decompression via a bullet hole?


While I try to never say never, I think there's no such
thing...or damned near no such thing at least.
--

-Gord.

What do readers think is the result of decompression via a bullet hole?

While I try to never say never, I think there's no such
thing...or damned near no such thing at least.

Yeah, one is reluctant to say "never" when random violence and complex
systems come together. The obvious counterexample to the
"convertible 737" that landed safely is the DC-10 that didn't do so
after loss of its cargo door.

However, with bullet holes, hopefully we're not talking about
catastrophic failures of large chunks of airplane.[1] And as for air
loss through bullet holes or even a failed window, consider WaltBJ's
calculation in light of the fact that you don't have to maintain
pressure in a holed cabin[2] *indefinitely* -- just long enough to
keep everybody breathing while you divert.


Finally, consider all this in post 9/11 perspective. We now know that
the bad guys' goal might be to destroy a ground target with the
aircraft. If the consequence of doing nothing is the loss of the
aircraft and all souls aboard anyway, PLUS great death or destruction
on the ground, that changes the sorts of risks you are willing to take
in the name of prevention.


If there is an armed marshal on board, you open the door not only for
cases of intermediate severity (e.g., plane crashes but does not
strike its target), but also for the best case -- he stops the bad
guys, maybe if you're lucky one or more of them survive (dead people
are hard to interrogate), and the aircraft makes a safe landing with
all the good guys still in one piece. And it strikes me as a better
than hand-to-hand by unarmed passengers -- which is still Plan B
should the marshal fail.


Hoping the deterrent effect will be enough,
--Joe

[1] I wonder how much of the popular imagination on this subject comes
straight from "Goldfinger," whose eponymous villain (if memory serves)
goes through the shot-out cabin window of a Lockheed Jetstar. I'd have
thought someone of his luxuriant specifications would've self-patched
almost anything short of complete loss of a door, but no. Whereupon
our hero and the lady du jour set some kind of record for egress under
duress. But I digress.

[2] I think a reasonable further assumption is that the amount of ammo
involved is modest. If there are a LOT of bad guys in one plane, or
they have guns of their own and can fort up for an extended shootout,
we have bigger problems than calculating the number of holes you can
poke in an airplane before somebody hits something important that the
flight crew can't settle with switchology.

"Ad absurdum per aspera" wrote in message
om...
What do readers think is the result of decompression via a bullet
hole?

While I try to never say never, I think there's no such
thing...or damned near no such thing at least.

Yeah, one is reluctant to say "never" when random violence and complex
systems come together. The obvious counterexample to the
"convertible 737" that landed safely is the DC-10 that didn't do so
after loss of its cargo door.


The problem here was not the depressurisation but the collapse
of the floor through which control cables were routed. Subsequent
to that incident changes were mandated to prevent such
recurrences.

However, with bullet holes, hopefully we're not talking about
catastrophic failures of large chunks of airplane.[1] And as for air
loss through bullet holes or even a failed window, consider WaltBJ's
calculation in light of the fact that you don't have to maintain
pressure in a holed cabin[2] *indefinitely* -- just long enough to
keep everybody breathing while you divert.


Not even that long, just long enought to reduce altitude to
10,000 ft or so.

Keith

"Ad absurdum per aspera" wrote

[1] I wonder how much of the popular imagination on this subject comes
straight from "Goldfinger," whose eponymous villain (if memory serves)
goes through the shot-out cabin window of a Lockheed Jetstar.

And one of the "Airplane" disaster movies. George Kennedy describing loss of
a window, or hole in the skin as 'catastrophic'.

Pete