FAA Sport Pilot Airplane (SPA)Aircraft Performance and SystemsHard
A pilot departs an airport where the current altimeter setting is correct, but the outside air temperature is significantly colder than standard for that altitude. Compared to the indicated altitude on the altimeter, the airplane's true altitude will be
- Athe same as indicated altitude
- Bhigher than indicated altitude
- Clower than indicated altitude
- Dunpredictable without additional data
Show answer & explanationAnswer & explanation
Correct answer: C. lower than indicated altitude
In colder-than-standard air, air is denser, so pressure levels are compressed closer together than standard, causing the airplane to actually be lower than the altimeter indicates. This is summarized by the memory aid 'from hot to cold or high to low, look out below,' warning pilots that true altitude may be lower than indicated in cold temperatures, especially critical near mountainous terrain.
Why the other options are wrong
- A. Temperature deviations from standard always introduce some altimeter error unless a correction is applied.
- B. This would be true in warmer-than-standard conditions, not colder.
- D. The direction of the error is predictable based on the temperature deviation from standard.
Temperature Effect on Altimetry
Non-standard temperatures cause the altimeter to misrepresent true altitude because it is calibrated for standard atmospheric conditions.
- Colder than standard: true altitude is lower than indicated
- Warmer than standard: true altitude is higher than indicated
- Mnemonic: 'From hot to cold or high to low, look out below'
- Most critical when flying over mountainous terrain in cold weather
Memory trick: Cold air shrinks the atmosphere — you're lower than you think