Last
week, (early September), nine people, including the pilot, were believed to have been killed
in the plane while it made a flight at 25,000 feet across Australia from Perth, until
it ran out of fuel and crashed 3200 km away on the shores of the Gulf of
Capentaria in Queensland. The circumstances of the accident appear
to be similar to the crash of the Lear Jet which took the life of the
famous golfer, Payne Stewart in the United States a few months ago. Although
there are no official confirmation of the cause from the Civil Aviation
Authority until it has completed the investigation, a likely scenario
would be a slow depressurization of the aircraft cockpit and cabin.
This will consequently result in hypoxia - a lack of oxygen in the blood.
Can
you recognize hypoxia ? The answer is no.. you may become euphoric (happy) and gradually loose consciousness. Can you feel the
depressurization ? The answer is yes.. if it is a rapid
depressurization because your ears will pop out ! If the
depressurization is very slow, then you may not be aware unless you look
at the cabin altitude indicator. All modern aircraft, including the
Boeing 777, has a cabin warning system, in the form of a warning horn,
that sounds in the cockpit when the cabin altitude exceeds 10,000 feet.
If
the cabin in the aircraft continues to depressurize to above 13,500
feet, the passenger oxygen masks automatically deploy and a pre-recorded
emergency announcement activates. (Now you know why you have to pay
careful attention to the emergency briefings every time you fly !
). In the Boeing 777, up to about 43,000 feet, the
aircraft can still maintain a comfortable cabin altitude of 8000
feet.
Airline
pilots have been trained and tested regularly on depressurization
procedures. Amongst other steps, they have been trained to don their
oxygen masks immediately and descent to 10,000 subject to terrain
clearance. If you are sitting quietly, your time of useful
consciousness will be 30 seconds at 40,000 feet, 75 seconds at 30,000 feet
and three minutes at 25,000 feet. This is the period between the
individual being deprived of his oxygen supply and becoming so affected by
hypoxia that he is unable to cope with an emergency.
Note:
This is a personal view. Kindly refer to my Disclaimer
The
above answer partly arose from a question by Daniel McAloon from Perth,
Australia. (he asked me about pressurization problems just days before the King Air tragedy)
