Since my practical exam is coming closer, I'm also reviewing the theory lessons. Since a part of the ULM exam is questions on those subjects.

Today I was reviewing "Human Factors". So I'll just write some summaries for myself. Human Factors deal with how the act of flying influences your body and judgment.

Warning: always double check the stuff I write here ... it's my personal notes.


Hypoxia is an oxigen shortage in the blood. At its worst, it is deadly. At its lightest it impacts your nigh vision.

Most of the issues occur when flying at altitudes of 5000 ft and higher. As the air pressure gets lower so does the oxygen pressure (21%), which means the blood gets less oxygen to carry through the body.

The first symptoms occur usually at 10.000 ft, when no additional oxygen is provided. Apparently you experience euphoria and you feel like you are performing optimally, but in fact this feeling is unjustified and your ability to perform tasks has already diminished.

If the hypoxia continues, it will become harder to breath, you'll get head-aches and even worse you can get "cyanosis" (blue discoloration) and eventuelly unconsiousness.

It's important to recognize hypoxia fast and take corrective measures by providing additional oxygen and reducing altitude.

If a person has trouble breathing at lower altitudes (< 5000 ft), it's more likely to be an issue of hyperventilation. But when in doubt, always assume it's hypoxia:

  • Hypoxia -> Unconsiousness -> Death
  • Hyperventilationo -> Unconsiousness (worst case) -> Recovery

Hypoxia gets worse as your altitude increases. It's estimated that over 40.000 ft you have only about 12 seconds of time to react before you are unconsious. But it 30.000 ft this is already about 40 seconds. At 20.000 ft this is 5 to 10 minutes.

If a decompression happens in an airliner cruising at 38.000 ft, the pilots would need to apply oxygen masks quickly, but the passengers as well. The pilots will have to descend as quickly as possible.

As sudden decompression is normally easy to spot, there will be wind, mist, pain, ... slow decompression is even more dangerous since you might slowly spiral into hypoxia and judgment may be impaired before you realise what is happening.

All that said, for flying an ULM, at least for what I plan, this won't really be an issue. We rarely go over 2.500 ft.

Decompression sickness

A sudden pressure loss causes issues in your body because nitrogen that is solved in the blood suddenly becomes small bubbles (think about opening a champagne bottle).

The various symptoms have names:

  • The Bends: bubbles in the joints cause pain. A tendency is to move, but better is to remain still
  • Creeps: small bubbles under the skin, giving itches
  • Chokes: bubbles in the lungs, caughing
  • Staggers: impact of the bubbles on the nervous system. Can cause nausia, vision problems, ...
  • Collapse: general malaise

More stuff

I'll try to write some summaries on the various courses now and then. For myself, mostly.