When flying into an area colder than standard temperature, would the indicated altitude be higher or lower than the true altitude?

• A. Lower
• B. The Same
• C. Higher
• D. Cannot determine

Answer: (C)

Indicated altitude is read from ambient pressure using the standard atmosphere model. When air is colder than standard, the vertical pressure gradient becomes steeper, so at a given true geometric height the pressure you experience is lower than the standard model would predict. The altimeter interprets this lower pressure as being higher up, so it shows a higher altitude than your true altitude. In other words, colder-than-standard conditions make the indicated altitude higher than the actual altitude. The opposite would occur in warmer-than-standard conditions, where the indicated altitude would be lower than the true altitude.