Punctured pressure cabin.

From: "M. J. Powell"


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?
M.J.Powell

What do you think will decompress an airliner cabin faster: An errant round
fired by an air marshal puncturing the cabin skin, or, the detonation of a
Richard Reid type jihadi nut case's shoe bomb because the air marshal wasn't
armed and couldn't drill him right between his beady eyes at the first
opportunity?

I'll take my chances with the air marshal's gun thanks.
Dave

Cub Driver wrote:

A normal bullet hole would be no problem. There's already a much
larger vent to the outside, which stabilizes cabin pressure against
the fresh & heated air being pumped in from the engines. People
smarter than I say that this hole is about three inches in diameter.



Dunno about smart but yes the 'hole' is indeed 3 or 4 inches wide
(and there's two usually) but they're not wide open all the time
(only when 'dump' is selected). They have another valve portion
which mates with them and regulates the 'outflow' to regulate the
cabin pressure which controls the 'cabin altitude'.

The pressurization regulator normally allows the cabin altitude
to slowly climb to roughly 8,000 - 9,000 feet while the a/c is
climbing to 35,000 - 40,000 feet. This puts the 'differential
pressure' (between the cabin and the outside pressure at roughly
8.5 PSID. (Pounds Per Square Inch Differential). This may not
sound like much but with a huge area such as a 747's cabin
there's a tremendous potential force there. That's why a small
explosion that rips a good sized hole in the skin can have
disastrous effect (No, a bullet hole is no problem as several
have mentioned)
--

-Gord.

"B2431" wrote in message
...
From: Cub Driver

snip

As to the possibility of explosive decompression, as I understand the
matter, it could happen if a bullet fractured a window

It would still be only annoying. A few ear aches and a lot of noise along
with
oxygen masks dropping. The person sitting next to the window might lose
his
reading material or dinner.

This has been discussed here before and a Google search would turn up a
lot of
information.

Dan, you are forgetting that there was indeed documented evidence of a
passenger being sucked out of a blown window brought out during that
discussion--a TAM Fokker F28 turboprop somwhere over Brazil (see:
www.crashdatabase.com/cgi-bin/
webdata_crashdatabase.cgi?cgifunction=Search&Airli ne=%5ETAM%24 ). There was
also a fatality during a 1989 Piedmont Airlines 737 rapid decompression
(www.canard.com/ntsb/ATL/89A099.htm ). As to the non-fatal effexcts, the
experience of an Aer Lingus 737 tends to point to some rather significant
injuries during a 1999 depressurization accident, with lots of ruptured
eardrums and severe nosebleeds, etc. I would not disagree that these
potential problems are far outweighed by the threat of some whacko with a
knife/bomb/etc., said whacko being dispatched by an air marshal, even with
the remote potential of causing a rapid decompression being preferrable to
the alternative. But the effect of such a decompression is likely going to a
bit worse than cleaning your tray table off and causing a few earaches.

Brooks



Dan, U. S. Air Force, retired

From: "Kevin Brooks"
Date: 1/1/2004 1:01 AM Central Standard Time
Message-id:


"B2431" wrote in message
...
From: Cub Driver

snip

As to the possibility of explosive decompression, as I understand the
matter, it could happen if a bullet fractured a window

It would still be only annoying. A few ear aches and a lot of noise along
with
oxygen masks dropping. The person sitting next to the window might lose
his
reading material or dinner.

This has been discussed here before and a Google search would turn up a
lot of
information.

Dan, you are forgetting that there was indeed documented evidence of a
passenger being sucked out of a blown window brought out during that
discussion--a TAM Fokker F28 turboprop somwhere over Brazil (see:
www.crashdatabase.com/cgi-bin/
webdata_crashdatabase.cgi?cgifunction=Search&Airl ine=%5ETAM%24 ). There was
also a fatality during a 1989 Piedmont Airlines 737 rapid decompression
(www.canard.com/ntsb/ATL/89A099.htm ). As to the non-fatal effexcts, the
experience of an Aer Lingus 737 tends to point to some rather significant
injuries during a 1999 depressurization accident, with lots of ruptured
eardrums and severe nosebleeds, etc. I would not disagree that these
potential problems are far outweighed by the threat of some whacko with a
knife/bomb/etc., said whacko being dispatched by an air marshal, even with
the remote potential of causing a rapid decompression being preferrable to
the alternative. But the effect of such a decompression is likely going to a
bit worse than cleaning your tray table off and causing a few earaches.

Brooks



Dan, U. S. Air Force, retired

I was referring to the blown out window. The passenger you refer to was blown
out a six foot hole according to your cite.

I agree a big chunk of skin suddenly departing the aircraft can cause major
damage and fatalities like the Hawaii Air stewardess deplaning prematurely.
There was also a case in the 1970s of a DC-10(?) where the aft cargo hatch blew
and took a row or two of seats with it.

On the other hand in the late 1980s a C-141B departed Eglin AFB and a hatch
over the cargo compartment blew. One of my men was standing directly below it
at the time. He noticed sudden day light, very loud noise and a bit of pain. I
believe the aircraft was at approximately 30 kilofeet at the time. It returned
to Eglin, made a safe landing and everyone sent to the base hospital for
evaluation.

Dan, U. S. Air Force, retired

A normal bullet hole would be no problem. There's already a much
larger vent to the outside, which stabilizes cabin pressure against
the fresh & heated air being pumped in from the engines. People
smarter than I say that this hole is about three inches in diameter.

More detail on this: over on rec.aviation.piloting, there's a parallel
and very busy thread on this same subject. Here's what a Big Spam Can
Driver had to say on the subject of the vent hole(s):

"Actually, a little bigger. There are two outflow valves that work in
tandem. On the 747 they're located on the aft belly, and each is a
touch smaller in area than one aircraft window -- an oval about 4in by
12in. There are also two relief valves on the left side of the
airplane, and they are about 8" in diameter."

So upon reflection it doesn't seem that even the blow-out of a window
could cause more than terror and discomfort, especially since it would
almost certainly be followed by an emergency descent to lower
altitude.

One of the pilots commented: "I always wear my seat-belt when flying.
Don't you?" Something to add to your resolutions for 2004


all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

Dan, you are forgetting that there was indeed documented evidence of a
passenger being sucked out of a blown window brought out during that
discussion--a TAM Fokker F28 turboprop somwhere over Brazil

I'd rather give up the guy in the window seat than go down with the
airplane onto Times Square.

Again I say: fasten your seat-belt when flying!

all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

Another question is if the terrorist is female will she still get the 72
virgins when she is "martyred?"

Perhaps she gets multiplied into 72 virgins.
all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

And more detail yet. This too from rec.aviation.piloting:

************************************************** **********************

The comments below are applicable to modern commercial Pax A/C. Anyone
familiar with the structure of an A/C will immediately ROFL at the
idea of a 9mm bullet penetrating the external skin if fired from
inside the cabin.

It would take a substantially more powerful weapon than a 9mm to cause
a "Window Failure", even then impact would have to be near 90 degrees
because of their "Plug design, plus they are thicker in the center
than the edge This curvature is on the inside.

The same applies to a bullet exiting through the A/C skin. Consider
between what is seen as the interior cabin wall & the "External Skin"
of the A/C is a layer of insulation, assorted wiring, plumbing in
some places, plus untold ribs, stiffeners, & other assorted structural
components all of which have some "Curvature" to them. All these
components are riveted together through "Lap Joints". All
joints/connections are sealed with "Sealant" of varying strengths.

The structure of an A/C is designed to flex, expand, & contract as the
A/C goes thru pressurization/de-pressurization cycles.

There are a few places a "Very High Velocity Bullet" of large caliber
could possibly exit the external skin if it the internal point of
impact was at a "very specific angle, very close to 90 degrees to
external skin" if fired from close range internally. Consider all the
materials described above a bullet would have to impact/penetrate,
without its path being diverted by some degree of ricochet.

************************************************** ******

(Again: the above is quoted from rec.aviation.piloting)


all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

B2431 wrote:

: I agree a big chunk of skin suddenly departing the aircraft can cause major
: damage and fatalities like the Hawaii Air stewardess deplaning prematurely.
: There was also a case in the 1970s of a DC-10(?) where the aft cargo hatch blew
: and took a row or two of seats with it.

IIRC there have been incidents with the cargo hatches of DC-10s,
but not limited to the loss of a number of seats; the entire
aircraft was lost --- depressurisation of the cargo bay
caused the cabin floor to collapse, destroying the control
runs.

As a result, modern aircraft were designed to have vents around
the cabin floor.

Emmanuel Gustin

In message , Cub Driver
writes

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

snip

So are you worse off risking explosive decompression, or of crashing
into Times Square at midnight?

As to the possibility of explosive decompression, as I understand the
matter, it could happen if a bullet fractured a window (though not if
it went through the skin). That's a mere possibility, as opposed to
the certainty of a suicide dive, absent the sky marshal.

A normal bullet hole would be no problem. There's already a much
larger vent to the outside, which stabilizes cabin pressure against
the fresh & heated air being pumped in from the engines. People
smarter than I say that this hole is about three inches in diameter.

I'm glad you mentioned 3" in diameter. During my RAF service my wireless
mechanics had to pass a camera cable from a bomb bay into the pressure
cabin in a Valiant. To my surprise they found a hole about 3" diameter
in a convenient place.

I said 'surprise' because I was in Signals and knew nothing about the
structural properties of the aircraft. I imagined that the pressure
cabin would be tightly sealed.

What about the loss of a window due to bullet strike? Would there be
structural failure?

Mike
--
M.J.Powell