Definition
The minimum runway length a transport-category jet airplane must have available to land safely under the conditions of the planned operation. For turbojet airplanes operating under FAR Part 121, it is the actual demonstrated landing distance from 50 feet above the runway threshold to a full stop on a dry runway, divided by 0.6 (a 60% factor that builds in a safety margin). For wet runways, an additional 15% is added on top of that. The result is the runway length that must be available at the destination for the planned landing weight.
Plain English
The shortest runway you are allowed to land on, given how much the airplane weighs and what the runway and weather are like. It is longer than the distance the airplane actually needs to stop, because the rules build in extra room as a safety cushion.
Context Anchor
Seen when planning a jet landing, checking runway suitability, or comparing the airplane’s landing performance with the runway length available at the destination or alternate airport.
Derivation
In aviation, “field” is an older word for an airport or landing area, not a farm field. “Length required” means the amount of landing area the airplane must have available for the landing to be acceptable under the stated conditions.
Why Pilots Care
Determines whether the intended runway is long enough to prevent a runway overrun.
Intuition Check
Do not read “field” as grass or open land here. In this term, “field length” means usable landing distance at an airport, usually runway length. Do not treat “required” as a rough suggestion. It means the length needed by the airplane’s performance data for the stated landing conditions.
Example Sentence 1
Before dispatch, the crew checked that the landing field length required at the destination was less than the runway available, including the 15% wet-runway adjustment.
Example Sentence 2
A headwind reduced the landing field length required, giving the pilot more margin on the shorter runway.