A crew is departing on a very cold winter morning with the surface temperature well below the ISA standard for the airport elevation. What effect does this cold temperature have on the aircraft's true altitude compared to its indicated altitude?
- ATrue altitude will be lower than indicated altitude, placing the aircraft closer to terrain than displayed
- BIndicated and true altitude will remain identical regardless of temperature
- CTrue altitude will be higher than indicated altitude
- DTrue altitude will equal indicated altitude only if pressure is also nonstandard
Show answer & explanationAnswer & explanation
Correct answer: A. True altitude will be lower than indicated altitude, placing the aircraft closer to terrain than displayed
In cold temperatures colder than standard, the atmosphere is denser and pressure levels are compressed closer to the surface, causing the altimeter to indicate a higher altitude than the aircraft's true altitude. This means the aircraft is actually lower than indicated, which is a critical safety concern near terrain or during instrument approaches — often summarized as 'high to low, look out below' but applied to temperature as well as pressure.
Why the other options are wrong
- B. Temperature does affect the relationship between true and indicated altitude.
- C. This is backward; cold temperatures cause true altitude to be lower, not higher, than indicated.
- D. Temperature error occurs independent of pressure-setting errors.
Cold Temperature Altimetry Error
An error in which colder-than-standard temperatures cause an altimeter to indicate a higher altitude than the aircraft's true altitude.
- Cold air is denser, compressing pressure levels closer to the ground
- Aircraft's true altitude is lower than indicated in cold temperatures
- Most critical during approaches near terrain in very cold conditions
Memory trick: Cold air, low true altitude — 'from hot to cold, look out below' applies to temperature too