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

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.

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.