FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsMedium
During cruise at FL390, a transport aircraft experiences a rapid (explosive) decompression due to a structural failure. What is the most urgent physiological hazard requiring the crew to don oxygen masks without delay?
- ARapid cabin temperature increase leading to hyperthermia
- BRapid increase in cabin altitude producing hypoxia within a very short time of useful consciousness
- CExcess cabin pressure differential causing barotrauma to the lungs
- DCarbon dioxide buildup from a failed air conditioning pack
Show answer & explanationAnswer & explanation
Correct answer: B. Rapid increase in cabin altitude producing hypoxia within a very short time of useful consciousness
A rapid decompression at FL390 causes the cabin altitude to jump almost instantly to the aircraft's actual altitude, giving occupants a time of useful consciousness of only seconds without supplemental oxygen. This makes hypoxia the immediate, life-threatening hazard, not temperature or CO2 buildup.
Why the other options are wrong
- A. Cabin temperature does drop, not rise dramatically, and is not the primary immediate hazard.
- C. Decompression relieves pressure differential rather than increasing it, so barotrauma from excess pressure isn't the concern here.
- D. CO2 buildup is a slow process unrelated to sudden decompression.
Rapid Decompression Hazard
Sudden loss of cabin pressurization causes cabin altitude to rise almost instantly to aircraft altitude, drastically reducing time of useful consciousness.
- Time of useful consciousness is seconds at high cabin altitudes above FL350
- Immediate oxygen mask use is required
- Cabin temperature typically drops sharply due to adiabatic cooling and fogging may occur
Memory trick: Boom goes the cabin — seconds of consciousness, mask on now!