Re: Cabin Depressurization

Date:         06 Jan 2000 01:26:08 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
References:   1 2
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>> 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/
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"The average dog is a nicer person than the average person."
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