This glossary is written for virtual airline and flight simulation use within Virtual Air Canada Airline. It is not intended as a real-world aviation reference.
FL
Flight Level
A Flight Level is a standard way of expressing altitude in aviation using a reference pressure setting of 1013.25 hPa (29.92 inHg), also known as the International Standard Atmosphere (ISA) pressure. Flight levels are expressed in hundreds of feet - FL350 corresponds to 35,000 feet indicated on an altimeter set to 1013.25 hPa. This standard reference is used by all aircraft at or above the transition altitude, ensuring a common vertical reference that allows consistent separation between aircraft regardless of local weather pressure variations.
The transition altitude (TA) is the altitude at or above which aircraft switch their altimeters from local QNH to the standard pressure setting of 1013.25 hPa and begin reporting altitude as a flight level. Below the transition altitude, pilots use QNH (local sea-level pressure) and report altitude in feet above mean sea level. Transition altitudes vary by country - they are 18,000 feet in North America, typically 3,000-6,000 feet in parts of Europe, and vary further elsewhere. The corresponding level at which pilots transition back from flight levels to QNH on descent is called the transition level (TL), and it is published on approach charts and communicated by ATC.