FAA Instrument Flight Instructor (FII)WeatherHard
An aircraft is flying at a constant indicated altitude using the current altimeter setting while crossing from a warm air mass into a significantly colder-than-standard air mass, without any temperature correction applied. What primary hazard should the pilot recognize?
- AThe altimeter under-reads baro pressure changes, producing no significant altitude error
- BIndicated altitude will read lower than true altitude, causing the pilot to fly too high
- CTrue altitude will be lower than indicated altitude, reducing obstacle and terrain clearance
- DTrue altitude will be higher than indicated, risking a traffic conflict with aircraft above
Show answer & explanationAnswer & explanation
Correct answer: C. True altitude will be lower than indicated altitude, reducing obstacle and terrain clearance
Colder-than-standard air is denser, causing pressure levels to be compressed closer together near the surface. The altimeter, calibrated to standard atmosphere, will indicate a higher altitude than the aircraft's true altitude — summarized by the mnemonic 'from hot to cold, or high to low, look out below.'
Why the other options are wrong
- A. The altimeter does respond to pressure changes normally; the error results from non-standard temperature, not a malfunction.
- B. This reverses the relationship; indicated altitude reads higher than true altitude in cold air, not lower.
- D. This describes the opposite (correct) relationship — true altitude is actually lower, not higher, in cold air.
Temperature Error on Altimeter
When flying from warm air into colder-than-standard air without correction, true altitude is lower than indicated altitude because cold, dense air compresses pressure levels closer together near the surface.
- 'High to low or hot to cold, look out below'
- No mechanical correction is built into standard altimeters for temperature
- Most significant hazard in cold weather operations near terrain/obstacles
- Cold temperature correction charts/tables should be applied on approach
Memory trick: Cold air squeezes you down — look out below!