In revisiting the recent crash/disappearance of an almost
new TBM900 many questions arise.
Perhaps the most cogent, why was there no perception of hypoxia/anoxia on the part of
the pilot? After reviewing communications between the pilot and ATC, there
never was a mention of a loss of cabin pressure, which leads to hypoxia etc.
An important question to answer is: why the pilot did not
acknowledge any of the indications of a high cabin altitude that should have
been available on his instrument panel? His actions indirectly confirm that he
didn’t consider anoxia an immediate threat. Was all the low cabin oxygen
detection equipment working properly?
A normal response by a trained, experienced pilot as he
was, would have been: declaration of an emergency and extremely rapid descent
to a lower altitude such as 10000 feet. Therefore one might conclude that
normal thought processes were compromised. This could have been secondary to
some degree of hypoxia. According to Harrison
et al, writing in Principles of Internal Medicine: “When hypoxia is
general, all parts of the body may suffer some impairment of function, but
those parts which are most sensitive to the effects of hypoxia give rise to
symptoms which dominate the clinical picture. The changes in the Central
Nervous System are especially important, and here the higher centers are
most sensitive. Acute hypoxia, therefore, produces impaired judgment,
motor incoordination and a clinical picture closely resembling acute
alcoholism.”
I remember well an
emergency decent that I experienced as a
passenger riding in the cockpit of an FAA Boeing 727 out of Oklahoma City in
1997. I was riding “up front” as a passenger while doing a summer internship at
The Aero-Medical Institute. We were at approximately 30,000 feet, when the
Captain announced loss of pressurization. There was a lot of hissing, oxygen
masks dropped like flies and we all struggled to place the masks on correctly
as rapidly as possible. The pilot advised us all through the intercom:” loss of
cabin pressure, put on masks”. The quick to don masks were on the flight crew
and me in seconds. That is all the time one has, in reality, before symptoms of
hypoxia will appear. The actual time depends to a great deal on the altitude
the decompression occurs.
The pilot deployed everything he could in seconds to get
us down rapidly. First the throttles retarded. Then flaps, spoilers and gear
deployed, essentially simultaneously. And we were headed down at more than
10,000 feet per minute in a continuous series of steep turns. I don’t know the
actual time, as I was holding on for dear life. Finally when we reached about
10,000 feet things slowed down. The
loose papers were gathered up and we could start to take off our masks. It was
a very valuable lesson for any pilot to experience. I had been through a simulated decompression
in the training area a few days previous to the flight. So I was somewhat
prepared, although the physical effects of all the actions of the rapidly
descending, corkscrewing airplane are hard to describe, and so much more
dramatic than in the simulator.
I had one other altitude adventure in the old days. As a
fairly newly licensed pilot, I was headed to Boston from Syracuse in an older
Cessna 182. As I was only licensed for VFR flight, I had to plan to avoid the
clouds, which were forecast to be broken along the route. By the time I was
halfway to Albany, the clouds began to thicken. I had to decide whether to keep
on going or keep dropping lower to get under the developing cloud layer, or
turn back. I decided to keep going and therefore began to climb to get on top.
That climb continued until I was well past Albany and ended up at 15,500 feet.
Although I knew about hypoxia, I never had really experienced it. That was
going to change on this flight. I noted that my breathing rate had increased,
and that I had developed a slight headache. My ability to function seemed ok
though. But I knew that I really couldn’t plan on going any higher. I probably
had also reached the service ceiling of the bird I was flying anyway. If I had
to continue much longer at 15,500 feet I decided that I would have to declare
an emergency and do an IFR descent as I had no Oxygen aboard. Fortunately as I
reached for the microphone, I noted that the clouds below starting to thin,
with glimpses of the ground. I immediately started to descend and was able to
land outside Boston at Hanscom Field under VFR conditions. That trip was a
major stimulus for my continuing with my IFR training and getting my ticket.
In summary. Hypoxia is a very real insidious hazard that threatens
every pilot. At the earliest sign of it, quickly put on your readily available
O2 mask if available. If not proceed to an immediate lower altitude if possible
and declare an emergency.
Happy, safe clear headed flying.
Reference: See FAR 91.211 Which goes further into anoxia and when supplemental Oxygen is to be used.
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