Definition
The actual height of an aircraft above mean sea level (MSL), expressed in feet MSL. True altitude reflects the aircraft's real vertical distance above sea level after correcting indicated altitude for nonstandard temperature and pressure variations.
Plain English
How high the aircraft really is above sea level, after accounting for the fact that the standard altimeter reading is rarely exact in real-world conditions.
Context Anchor
Seen in altimeter discussions, flight planning, terrain clearance, and weather reports that use heights above sea level.
Derivation
True' here means 'actual' or 'real' — as opposed to the altitude shown on the instrument, which is an approximation. The word distinguishes the real height from the several other altitude types (indicated, pressure, density, absolute) that pilots also work with.
Why Pilots Care
True altitude determines actual terrain clearance and is essential for safe flight over mountains or in cold weather.
Grounding Statement
If average sea level were extended underneath the airplane, true altitude is the airplane’s height above that level.
Intuition Check
“True” does not mean perfect or more official here. It means the aircraft’s actual height above mean sea level, not its height above the ground.
Example Sentence 1
On a cold winter day, the pilot remembered that true altitude would be lower than the altimeter indicated, so he added an extra cushion when crossing the ridge.
Example Sentence 2
In warmer than standard air the aircraft's true altitude was higher than the altimeter showed.