Pressurization and oxygen
The cabin altitude, the differential limit, decompression, and the 91.211 oxygen rules.
14 min read · The complex airplane
After this lesson you can
- Explain why airplanes are pressurized and what limits how much they can be pressurized.
- Distinguish isobaric operation from differential operation and interpret a cabin pressure differential.
- Distinguish explosive from rapid decompression and describe why time of useful consciousness drops so sharply with altitude.
- Apply the 14 CFR 91.211 oxygen requirements at the correct altitude thresholds.
Airplanes fly high for two concrete reasons: less drag for a given airspeed makes cruise more efficient, and altitude puts weather and turbulence below rather than in the way. Both reasons run straight into the same problem — above roughly 12,000 to 15,000 feet, the atmosphere no longer supports normal human function. Pressurization is the engineering answer, and it introduces a specific new risk that has no equivalent at lower altitude: the sudden loss of a breathable environment, with only seconds to respond correctly.
For a commercial pilot, the goal of this lesson is not to memorize the plumbing of a pressurization system. It is to read a cabin altitude correctly, recognize a decompression in the first few seconds, and know the oxygen thresholds in 14 CFR 91.211 by number, because at these altitudes there is no time to look them up.
The rest of this lesson
- 1.The circuit
- 2.Differential pressure and the two operating modes
- 3.Decompression
- 4.What exists for the seconds right after
- 5.What 14 CFR 91.211 actually requires
- 6.Choosing and using the equipment
- 7.Managing the compressed gas: the cylinder itself
- 8.Rapid decompression: what it does to the people, and what a malfunction looks like
These 8 sections, their figures, the checks along the way and the end-of-lesson quiz come with the CPL track. Paid once, yours for good.
Key terms
Try to recall each definition before turning the card.