What Is Transition Altitude? Definition & Meaning in Aviation
The transition altitude is the height at which pilots change from setting their altimeter to local pressure to setting it to standard pressure.
In plain language
Below it, altitude is measured using the local pressure (QNH) so that height above the ground is accurate. Above it, aircraft use flight levels.
Example
On climb out of an airport, the crew switches to standard pressure when passing the transition altitude, and on descent switches back.
Why it matters
The transition altitude explains why altitudes on a tracker can jump slightly during climb and descent, as the reference changes from local to standard pressure.