Definition
An ARINC 424 path and terminator leg type used in RNAV procedures that begins at a defined fix and continues on a specified track until the aircraft reaches a specified altitude. The leg ends when the altitude is achieved, regardless of distance flown, at which point the next leg begins.
Plain English
A segment of an instrument procedure that starts at a named point and tells you to fly a specific heading until you climb (or descend) to a target altitude. Once you hit that altitude, the segment is finished and you move on to the next part of the procedure.
Context Anchor
Seen in the coding behind instrument departures, arrivals, and approaches, especially when a procedure segment needs to end at an altitude instead of at another named point.
Derivation
In ARINC 424 path-terminator coding, each leg type is given a two-letter code. The first letter describes the path flown (here, F for a track from a Fix), and the second letter describes what terminates the leg (here, A for Altitude). So FA literally reads as 'Fix-to-Altitude.' Knowing the code is built this way makes other leg types (CA, VA, CF, DF, etc.) easier to read at a glance.
Why Pilots Care
Tells the FMS or autopilot exactly how to fly that portion of the procedure so the aircraft levels or climbs at the right point.
Grounding Statement
An FA leg means: start here, fly this track, and don't turn until you reach this altitude.
Intuition Check
Do not read “leg” as an airplane part; here it means one segment of the procedure. Do not expect an FA leg to end at a named waypoint—the altitude is what ends it.
Example Sentence 1
The RNAV departure begins with an FA leg from the runway end, requiring a climb on runway heading until reaching 1,500 feet before turning on course.
Example Sentence 2
After the FA leg the aircraft levels off and begins the next segment toward the final approach course.