Plain English Meaning

A way of stating altitude in the high-altitude environment, written as FL followed by three digits that represent the altitude in hundreds of feet, with every aircraft using the same standard pressure setting on the altimeter.

Full Definition

A standard altitude expressed in hundreds of feet above the 29.92 inches of mercury (1013.2 hPa) reference pressure setting. For example, FL 250 means an indicated altitude of 25,000 feet when the altimeter is set to 29.92. Flight levels are used at and above 18,000 feet MSL in the United States, where all aircraft set their altimeters to the standard pressure setting so that vertical separation between aircraft is consistent regardless of local pressure.

Context Anchor

Seen in high-altitude instrument flying, , and discussions of .