Critical Field Length

Critical field length is the longer of the accelerate-stop distance and the take-off distance over a 35 ft screen height, following an engine failure at the critical engine failure speed (V_EF). It represents the minimum runway length required for a safe take-off with the possibility of an engine failure.

Relationship to Balanced Field Length

When the accelerate-stop distance equals the take-off distance, the field is balanced. In many real-world scenarios, one of these two distances is longer — the longer one is the critical field length and must not exceed the available runway length (plus, where applicable, stopway and clearway). This is a fundamental transport category aircraft performance requirement under CARs Part VII.

Related Terms

See also: Balanced Field Length, Critical Engine.