Quick Facts
- Type
- Altitude Reference
- Definition
- An altitude expressed in hundreds of feet when the altimeter is set to 29
- Used By
- Pilots, ATC
Definition#
A flight level (FL) is a standardized altitude reference used when the altimeter is set to the standard barometric pressure of 29.92 inHg (1013.25 hPa). FL350 means 35,000 ft pressure altitude. Flight levels are used above the transition altitude.
Why It Matters Operationally#
Using flight levels ensures consistent vertical separation between aircraft regardless of local pressure variations. In the U.S., transition altitude is 18,000 ft. Above this, all aircraft use standard pressure.
Related Guides#
- How Airplanes Fly — The Complete Aviation Fundamentals Guide
- Density Altitude Explained
- Clear Air Turbulence Explained