Airliner Decompression Incidents (was Re: Denver in 2008) (long)

On Sun, 10 Sep 2006 20:54:19 GMT, Sea Wasp
<seawaspobvious@xxxxxxxxxxxxxxxxx> wrote:

Specifically, there is a LARGE difference between a pressurized
airliner hull sitting in a boneyard and one in the air. The one in the
air is moving at 500-600 miles per hour, and I am not QUITE so
sanguine about ignoring the chance that the COMBINATION of air
pressure difference *AND* super-tornado force winds acting on a
suddenly-appearing hole would not have some considerably worse effects.


Aloha Airlines 243, a 737, was probabaly the worst example of fuselage
failure in modern aircraft. While a large portion of the skin
stripped away, the underlying causes were found to be metal fatigue
(both from age and hard landings), "crevice corrosion" (the aircraft
operated in an over-ocean environment primarily, and salt got into
crevices from which standard washing procures failed to remove it.

A passenger reported - after the incident - that he had observed an
actual crack in the hull while boarding, but hadn't bothered to
mention it
..
{quote}

After the accident, a full-scale investigation was launched by the
United States National Transportation Safety Board (NTSB). It
concluded that the accident was caused by metal fatigue exacerbated by
crevice corrosion [3] (the plane operated in a salt water
environment). The root cause of the problem was failure of an epoxy
adhesive to bond the aluminium sheets of the fuselage together when
the B737 was manufactured. Where it failed to bond the two surfaces
together, water could enter the gap and start the corrosion process.
Since the corrosion products have a larger volume than the underlying
metal, the two sheets were forced apart, putting extra stress on the
rivets also used to hold them together. The age of the aircraft became
a key issue (it was 19 years old at the time of the accident and had
sustained a remarkable number of takeoff-landing cycles ? in excess of
80,000, well beyond the 75,000 trips it was designed to sustain).
Consequently, all major United States air carriers decided to retire
their oldest aircraft to prevent a recurrence. Also, aircraft now
receive additional maintenance checks as they age.

According to the official NTSB report of the investigation, a
passenger noticed a crack in the fuselage upon boarding the aircraft
prior to the ill-fated flight but did not notify anyone. The crack was
located aft of the front portside passenger door. This crack was
probably due to metal fatigue related to the over 89,000 compression
and decompression cycles experienced in the short hop flights by
Aloha, which was the second highest number of cycles in the worldwide
fleet of 737s at the time.

{end quote}

http://en.wikipedia.org/wiki/Aloha_Flight_243

United Airways flight 811 is a more likely example of a "worst case"
scenario. Where only one person was killed in the Aloha incident (a
flight attendant who was walking the aisle when the hull let go), 811
suffered several more casualties (body parts were found inside the #3
engine [which failed]).

However.

The cause of the faillure was a faulty door latch on a cargo door,
which allowed it to blow free.

Okay. We've got a great big stonking HOLE in the side of the airplane
- the door looks looks to be maybe four by eight foot in the pictures
i see - which is definitely bigger than the hole any conceivable
gandgun bullet is going to make, and, incidentally, involves actual
airframe damage, which the odds of a bullet hole causing are either
vanishingly small or nonextant.

And, apparently, as the door departed (i believe they hinge upward,
that's certainly the way i'd design cargo doors in a setting like
that) it peeled away a section of skin directly above it; i'd imagine
it was like a gigantic version of the older pull-type ringtab can,
where the tab pulls loose, and then strips out an ateched section of
metal.

(Here's a low-res but discernible picture of the damage
http://www.warman.demon.co.uk/anna/united.jpg, and here's an inside
view
http://en.wikipedia.org/wiki/Image:United_Flight_811_view_from_inside_hole.png)

But your "the COMBINATION of air pressure difference *AND*
super-tornado force winds acting on a suddenly-appearing hole" is
definitely present.

While i woudn't be very sanguine about repairing the fuselage and
operating that airframe again, please note that the damage was
confined to the hatch area and itsvicinity.

{quote}

As the 747 climbed to between 22,000 and 23,000 feet the R5 cargo door
tore open, decompressing the cabin and leaving a gaping hole. Five
rows of business class seats were blown out of the aircraft, along
with nine passengers, some of whom were drawn into engine three
(remains were later found in the engine)[1]. Severely injured, a
flight attendant was lying down beside the hole caused by the
decompression.

Because the cabin was no longer pressurized, the pilots initiated an
emergency descent to reach an altitude with breathable air. The
explosion had knocked the number three engine out and the number four
engine caught fire. Despite only partial flaps (a portion of the shed
fuselage damaged the flaps on one wing) and concerns over the plane's
landing gear and structural integrity, the crew made a perfect landing
and deployed all ten evacuation slides on the aircraft. The evacuation
was completed in 90 seconds, with no additional injuries occurring.
[edit]

Cause

The incident was most likely caused by improper wiring in the R5 cargo
door latching mechanism. At the time, the design of the 747-122
provided a small window situated flush against each of the cargo
doors, so that the ground crew could visually confirm that the doors'
latches were set to the locked position. There were, however, several
flaws in this design. It didn't allow a particularly close look at the
door latches, and it didn't show the entire latching mechanism, which
made the complete inspection of the latched door impossible.
Furthermore the circuit controlling electrical power to the doors was
faulty and could operate in flight, which caused the doors to unlock.
The R5 door, being an outward-opener, blew open and separated from the
fuselage. It took a large section of the aircraft's fuselage with it,
leaving the passenger cabin exposed to the elements at 22,000 feet. At
this point the aircraft was approximately 60 miles from Honolulu. It
managed to make a safe turnaround and a safe landing, after which an
evacuation was immediately carried out.

(end quote}

Note that, despite a goodly section of fuselage haveing been torn
offas the door ripped free, there was no further failure of the
airframe, nor was anyone other than those injured/killed in the
initial event particularly endangered.

And this was a LOT bigger hole than a bullet hole.

And now we come to American Airways flight 96, the so-called "Windsor
Incident".

Again, a cargo door blew out.

This is the one that falls into the "He couldn't do that again even in
an instant replay" category - with no rudder and limited elevator and
aileron control, the crew managed to turn the plane and land it
safely, using the throttles to steer and what little elevator
operation remained to maintain trim.

(http://en.wikipedia.org/wiki/American_Airlines_Flight_96)

This one was a DC-10 (Google Images couldn't come up with any pics),
and, in this case, replacing/upgrading the cargo door mechanism was
*not* made mandatory, and many airlines didn't apply it; two years
later (1974), Turkish Airlines Flight 981 was involved in a much worse
incident, resulting in the single worst air disaster until the
Tenerife 747 collision in 1977, and the worst single-aircraft fatal
until JAL 123 in '85.

However, what made this one so bad was that the door blew out during
climbout:

{quote}

a high speed crash into the forest at Ermenonville, France, only a few
minutes after take-off on the Paris-London leg. A defective latch on
the cargo door caused it to open in flight, resulting in an explosive
decompression. The decompression caused the cabin floor near the door
to fail, blowing six passengers out of the plane and severing the
control cables leading to the tail surfaces. With elevator control
lost, the plane lost horizontal stability and dived into the ground at
430 knots.

Although there was no radio contact made with the ground, ATC heard
the pilot Nejat Berkoz speaking with cabin crew in Turkish. On the
tape from the recovered cockpit voice recorder, an explosion was
heard, followed by a rush of air out of the plane. At this point
Berkoz asked "What has happened", and was told, "The fuselage has
burst!" During the 77 seconds after the decompression, the crew tried
desperately to control the plane, but the plane did not respond to any
of the attempts. At one point the crew did manage to raise the nose,
but it was too late, as the plane was just a few hundred feet above
the ground.

{end quote}

http://en.wikipedia.org/wiki/Turkish_Airlines_Flight_981

The problem (as with the Windsor Incident) was not so much the
decompression (and the damage apparently did not propagate
particularly far beyond the area of the hatch and the
immediately-attached skin/frame) but with the fact that the initial
damage knocked out the controls.

When it takes an entire cargo door ripping off to produce that kind of
damage, i would be quite willing to ride in a modern, well-maintained
airliner at cruising altitude and allow you to fire as many rounds
from standard handguns any old where you like inside the cabin (except
into me or into the flight crew).

--
mike weber (fairportfan@xxxxxxxxx)
============================
My Website: http://electronictiger.com
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