Newsgroups: sci.aeronautics.airliners
Date: 06 Jan 2000 01:26:07
From: Mary Shafer <shafer@rigel.dfrc.nasa.gov>
Subject: Re: Cabin Depressurization

"P. Wezeman" <pwezeman@blue.weeg.uiowa.edu> writes:

> 	Following the ValueJet fire and crash in Florida there was
> an article published in a magazine, it might have been the Atlantic
> Monthly, in which the author stated that at any given time there
> was a maximum atainable level of safety in aviation. There was
> a point of diminishing returns in adding safety features and
> equipment, since the safety equipment could itself malfunction,
> as had happened in the case of the ValueJet.
>
> 	The author also stated that emergency oxygen systems
> on airliners had never saved a single life. Is this true? Any
> counterexamples? I know of at least three explosive decompressions
> where most of the passengers survived: the DC-10 where the cargo
> door blew out over Canada, the Aloha Air 737 where the top of the
> forward fuselage came off, and the 747 that lost a cargo door
> over the Pacific. Did oxygen systems help in any of these cases?

This was in the Atlantic Monthly and can still be accessed, I
believe.  The author is the son (or possibly the grandson) of the man
who wrote the definitive book on how to fly an airplane ("Stick and
Rudder").  Their surname is Langewiesche (the elder is Wolfgang and I
think the Atlantic author is Richard).

I read this same article and was similarly surprised by the claim, so
I did a little looking around.  I checked the FAA, NTSB, and a couple
of non-US accident databases.  I have been able to find no case of the
emergency oxygen system on an airliner saving a single life or the
absence of one causing a fatality.  That Aloha Air 737 was too low for
it to be needed, as I recall (it occurred right after takeoff, at the
beginning of the beverage service, which starts at 10,000 ft MSL).
The two cargo door losses depressurized the airplanes slowly enough
that the emergency descent got them down before anyone died of hypoxia
or anoxia.  The closest I could come to an emergency O2-related
accident was one where the masks didn't drop as they should have, and
there were no fatalities.  I've got a query into a friend at the FAA,
though.

However, there are two important caveats to make.  The first is that
the absence of evidence isn't evidence of absence.  The second is that
complex accidents (say, for example, where the aircraft broke up in
flight and fell to the ground) are excluded; the O2 may have kept
someone alive long enough to die from the ground impact, for example,
but there's no evidence of this.

The DC-10 at Paris that crashed when the cabin floor collapsed onto
the control cables, jamming them, because of a decompression in the
cargo compartment, is an example.  It was just high enough for
the pressure differential to cause the structural failure, but not for
long enough for supplemental O2 to do anything more than keep
passengers conscious all the way to the ground, if (and that's a big
_if_) the masks deployed and the passengers were able to overcome g
forces and don them.

Airliners usually fly long flights at or below 40,000 ft.  Although
the time of useful consciousness is fairly short, death takes quite a
bit longer.  The emergency descent will get the airplane down into
breathable air long before people run out of O2.  Obviously, the
amount of O2 in the air increases constantly through the descent,
stringing out the time of useful consciousness.  After all, it's
something like more than twice as long at 30,000 ft as it is at
40,000 ft.

Of course, there have undoubtedly been cases where the bottled O2 on
board an airliner has saved a life, but this isn't the mass emergency
"masks will deploy" O2 system but just a standard O2 bottle and mask,
carried for individual use.  The O2 is there for people having heart
attacks or difficulty breathing or some other problem that O2 will
help.  That is, it's there for an individual emergency, not an
aircraft emergency.

None of this applies to military aircraft, particularly the aircraft
with canopies, not windows.  There are innumerable cases of the O2
system (either in normal or emergency mode) saving all aboard.
However, the assumption is that the pressurization is going to fail,
as the US military requires fighter and attack crew to use O2
throughout the flight.  Aircraft with canopies have latches that hold
the canopy down to the canopy rail, with a tube that fills with air
and seals the gap.  A faulty latch or leaky tube can render a cockpit
unpressurizable, which is why the crew of such aircraft are on O2 all
the time.  In addition, there's an O2 bottle in every ejection seat,
to tide the crew over during the freefall until the baro altimeter
takes control and throws the crewmember out of the seat and opens the
parachute at about 15,000 ft MSL.  In more extreme cases, with
aircraft cruising high enough that there are other dangers, the crew
wear pressure suits, even though the cockpit is pressurized as
described.

--
Mary Shafer    http://www.dfrc.nasa.gov/People/Shafer/mary.html
shafer@rigel.dfrc.nasa.gov     Of course I don't speak for NASA
Lead Handling Qualities Engineer, SR-71/LASRE
NASA Dryden Flight Research Center, Edwards, CA
For non-aerospace mail, use shafer@ursa-major.spdcc.com please

Newsgroups: sci.aeronautics.airliners
Date: 06 Jan 2000 01:26:08
From: kls@ohare.Chicago.COM (Karl Swartz)
Subject: Re: Cabin Depressurization

>> I know of at least three explosive decompressions
>> where most of the passengers survived: the DC-10 where the cargo
>> door blew out over Canada, the Aloha Air 737 where the top of the
>> forward fuselage came off, and the 747 that lost a cargo door
>> over the Pacific. Did oxygen systems help in any of these cases?

> That Aloha Air 737 was too low for
> it to be needed, as I recall (it occurred right after takeoff, at the
> beginning of the beverage service, which starts at 10,000 ft MSL).

Not quite.  They had just leveled off at their cruise altitude, though
that was only at FL240 so the air wasn't too thin.  They immediately
donned their oxygen masks and began an emergency descent at 4000 fpm or
so.  (This actually led to a suggestion by the NTSB that the FAA issue
an Operations Bulletin reminding operators of the admonishment in the
737 FCOM to "limit airspeed as much as possible and avoid high
manuvering loads" if structural integrity is in doubt.  Clearly, in this
case there was plenty of doubt about the remaining structural integrity!)

The Aloha 737 was equipped with a manifold-based oxygen system for
depressurization emergencies, and this was severed so it obviously did
not help.  Had there been oxygen generators (the sort which triggered
the ValuJet crash), I suppose they might have helped some passengers.

-- 28 Apr 1988; 737-297 N73711; AQ 243 ITO-HNL
  (details from Macarthur Job's Air Disaster, volume 2)

>The two cargo door losses depressurized the airplanes slowly enough
>that the emergency descent got them down before anyone died of hypoxia
>or anoxia.

The 747 over the Pacific was climbing between 22,000 and 23,000 feet
at the time of the initial event.  Again, not all that high, but with
a 10 x 15 foot hole I doubt that the rate of depressurization could be
characterized as "slowly."  The pilots donned their oxygen masks but
found no oxygen -- the supply and fill lines for the flightcrew oxygen,
as well as the supply line for the passenger oxygen system, ran below
the cabin floor and had been severed in the vicinity of the missing
cargo door.

-- 24 Feb 1989; 747-122 N4713U; UA 811 HNL-AKL
  (details from NTSB report NTSB/AAR-90/01)

Pete mentioned "over Canada" in conjunction with the DC-10 cargo door,
so presumably he was referring to the 1972 Windsor, Ontario incident and
not the 1974 crash near Paris.  Those accidents initiated at about 12,000
feet and 12,000-13,000 feet, respectively, both low enough for hypoxia
to not be an issue.  I can't find anything which mentions whether or
not the emergency oxygen systems were deployed in either accident, but
in the Windsor case an emergency descent was NOT executed because the
pilots were afraid of losing what little control they had.

In the Paris case, 77 seconds elapsed between decompression and impact,
so even if oxygen had been a factor, it wouldn't have been one for long.

-- 12 Jun 1972; DC-10-10 N103AA AA 96 BUF-LGA
-- 03 Mar 1974; DC-10-10 TC-JAV; TK 981 ORY-LON
  (details from Macarthur Job's Air Disaster, volume 1, and from The
  DC-10 Case: A Study in Applied Ethics, Technology, and Society)

--
Karl Swartz	|Home	kls@chicago.com		http://www.chicago.com/~kls/
		|Work	kls@netapp.com		http://www.netapp.com/
"The average dog is a nicer person than the average person."
  - Andrew A. Rooney

Newsgroups: sci.aeronautics.airliners
Date: 06 Jan 2000 01:26:09
From: kts@socrates.berkeley.edu (Katie Schwarz)
Subject: Re: Cabin Depressurization

P. Wezeman <pwezeman@blue.weeg.uiowa.edu> wrote:
>	Following the ValueJet fire and crash in Florida there was
>an article published in a magazine, it might have been the Atlantic
>Monthly, in which the author stated that at any given time there
>was a maximum atainable level of safety in aviation. There was
>a point of diminishing returns in adding safety features and
>equipment, since the safety equipment could itself malfunction,
>as had happened in the case of the ValueJet.

It was the Atlantic, and the author was William Langewiesche, son of
the _Stick and Rudder_ author.  You can read it online at
http://www.theatlantic.com//issues/98mar/valujet1.htm

--
Katie Schwarz
"There's no need to look for a Chimera, or a cat with three legs."
                         -- Jorge Luis Borges, "Death and the Compass"

Newsgroups: sci.aeronautics.airliners
Date: 06 Jan 2000 01:26:10
From: glpilotsrv@aol.com (GLPILOTSRV)
Subject: Re: Cabin Depressurization

In article <airliners.1999.1301@ohare.Chicago.COM>, "P. Wezeman"
<pwezeman@blue.weeg.uiowa.edu> writes:

>The author also stated that emergency oxygen systems
>on airliners had never saved a single life. Is this true? Any
>counterexamples? I know of at least three explosive decompressions
>where most of the passengers survived: the DC-10 where the cargo
>door blew out over Canada, the Aloha Air 737 where the top of the
>forward fuselage came off, and the 747 that lost a cargo door
>over the Pacific. Did oxygen systems help in any of these cases?

I would not doubt the statement. Drop down oxygen systems do not supply
oxygen under pressure. Above approximately 25,000 feet, oxygen needs to
be supplied under pressure, otherwise the hemoglobin will not absorb the
oxygen present.

The flight crews will have quick donning masks that will supply the
oxygen under pressure. The mask will actually inflate the lungs and the
user will have to forcibly exhale.

It was noted at the High Altitude and Flight Physiology training at ADW,
that unless the crew already was using oxygen, the best outcome of an
explosive decompression at high altitudes (35,000 feet+) would be the
crew would gray out during the process of donning the masks. Of course,
the worst outcome is the crew taking longer than the few seconds of
useful consciousness they have to don the masks and blacking out.

This is the reason that above 25,000 feet, if one crew member leaves the
flight deck, the remaining crew member is required to use supplemental
oxygen. Above 35,000 feet, regardless of number of crew members on the
flight deck, one crew member must utilize supplemental oxygen.

If you are on an aircraft when the overhead masks deploy, go ahead and
quickly pull the mask fully down (this starts the oxygen flow) and place
the mask over your nose and mouth. If this occurs at high altitude, just
plan on waking up with a slight headache after the crew has completed
the emergency descent.

Garrr