POSTED: Sunday, August
14, 2005 12:00:00 AM
UPDATED: Monday, August 15, 2005
An American Trans Air jet was
cruising over the Midwest at 33,000 feet
on May 12, 1996, when a blaring horn
sounded in the cockpit. The Boeing 727
was rapidly losing cabin air pressure.
Within seconds, the captain and the
flight engineer lost consciousness,
victims of a lack of oxygen. Only the
co-pilot, who had donned an oxygen mask
at the first sign of trouble, remained
conscious and able to fly the plane,
according to an official account of the
incident by the National Transportation
The plane, carrying 112 passengers
and crew, landed safely in Indianapolis
after diving to lower altitudes.
The incident demonstrated how quickly
a loss of pressure on a high-flying jet
can put lives in jeopardy.
Preliminary evidence from Sunday's
crash of a 737 in Greece suggests that
passengers and crew aboard Helios
Airways Flight ZU522 were not as lucky.
Two Greek air force F-16 pilots who
flew alongside the Helios jet saw the
co-pilot slumped over his controls. A
man told Greece's Alpha television that
he received a text message from his
cousin aboard the jet saying that the
pilots were unconscious.
Aviation experts say it's too early
to say why the flight from Cyprus to
Athens slammed into a mountain, killing
all 121 aboard. But investigators will
be focusing on whether the jet lost the
air pressure that allows people to fly
in comfort above 30,000 feet.
John Purvis, a former accident
investigator at Boeing, says jets have
lost pressure because of pilot errors,
improper repairs, corroded metal or
The puzzling thing for investigators
and pilots is that jets are designed to
withstand a loss of pressure. All
airline jets are equipped with pure
oxygen for pilots and passengers to
breathe in an emergency. Flight
attendants remind passengers of this
before every flight.
From the moment they learn to fly at
high altitude, pilots are trained how to
respond if pressure is lost. A warning
horn sounds if cabin pressure falls to
dangerous levels. Jets are designed to
allow pilots to rapidly descend to safe
altitudes in case of a problem.
Pilots repeatedly practice the
The NTSB's list of accidents since
1962 does not contain a single case of
mass fatalities on an airliner caused by
a loss of cabin air pressure alone. In
several cases, jets have broken open in
flight, but pilots always have been able
to descend and land if the plane stayed
in one piece.
``If it did decompress, I would not
expect it to result in the loss of the
airplane,'' says John Cox, a retired 737
pilot who works as an aviation safety
But events such as the American Trans
Air flight in 1996 show how quickly
pilots can get into trouble if they
don't have emergency oxygen when jets
People rapidly lose good judgment at
altitudes above 20,000 feet.
Above 35,000 feet, the air is so thin
that people can pass out in seconds.
Retired airline pilot Patrick Clyne
recalls training in a simulated
high-altitude chamber. At the equivalent
of 25,000 feet, he was asked to play
tic-tac-toe. ``It's insidious,'' Clyne
says. ``You start off real well. In a
matter of a very few seconds, you can't
even draw the box.''
On the 1996 flight, the NTSB
concluded that the captain did not
follow the checklist requiring that he
don an oxygen mask as soon as the
emergency horn sounded. The flight
engineer's mask apparently came off his
face, and he passed out.
The co-pilot, who had only flown in
that model of jet for 10 hours, few them
By ALAN LEVIN, USA