Definition
The difference between the altitude shown on the altimeter and the aircraft's actual altitude. It is caused mainly by non-standard atmospheric pressure or temperature, since the altimeter calculates altitude assuming standard conditions.
Plain English
How far off the altimeter's reading is from the height the aircraft is really at.
Context Anchor
Seen during altimeter checks, instrument flying, and any time a pilot compares the altimeter reading with a known airport elevation or assigned altitude.
Derivation
Altitude comes from the Latin word altus, meaning “high.” Error comes from a Latin word meaning “to wander” or “go astray.” Together, the term means the altitude reading has wandered away from the correct value.
Why Pilots Care
Even small altitude errors reduce terrain clearance margins and can cause airspace or approach deviations.
Intuition Check
Error does not mean the pilot necessarily made a mistake. Here it means the altitude indication is different from the value it should show.
Example Sentence 1
On a very cold day, altitude error can leave the aircraft significantly lower than the altimeter indicates, so the crew added a cold-temperature correction on the approach.
Example Sentence 2
Cold temperatures created a 150-foot altitude error, making the altimeter read higher than the aircraft's actual height.