Definition
A standard pressure altitude of 38,000 feet, expressed in the flight level system used at high altitudes. Flight levels are referenced to a standard altimeter setting of 29.92 inches of mercury rather than to the local pressure setting, so FL 380 indicates 38,000 feet above the standard pressure datum, not necessarily 38,000 feet above mean sea level.
Plain English
An altitude of 38,000 feet, measured using a standard pressure setting that all high-altitude aircraft share so they can fly at consistent, separated levels.
Context Anchor
Seen in high-altitude performance discussions, air traffic control clearances, and aerodynamics topics such as subsonic and supersonic flow.
Derivation
The term 'flight level' was adopted to distinguish altitudes flown on a standard pressure setting from altitudes referenced to local pressure. The number 380 is shorthand for 38,000 feet — the last two zeros are dropped, so '380' means 'thirty-eight thousand.'
Why Pilots Care
It provides standardized vertical separation between aircraft in high-altitude routes and RVSM airspace.
Analogy
Think of several people measuring from the same starting line. The measurement is useful because everyone is using the same zero point, even if the actual ground below them is not the same height.
Grounding Statement
At FL 380, the aircraft is operating in the 38,000-foot pressure layer, not simply 38,000 feet above the ground below.
Intuition Check
“Flight level” does not mean exact height above the ground. It means altitude based on a shared standard pressure setting; FL 380 is 38,000 feet on that standard setting.
Example Sentence 1
The crew leveled off at FL 380 and set cruise power for the long leg across the Atlantic.
Example Sentence 2
At FL 380 the crew checked fuel burn and cabin pressure during the cruise check.