Definition
An ARINC 424 path terminator leg, coded HF, that directs the aircraft to fly one complete holding-pattern circuit and end the leg back at the defining fix. Unlike a continuous hold, the HF leg is flown only once: the aircraft crosses the fix, flies the outbound leg, makes the procedure turn, intercepts the inbound course, and terminates the leg upon recrossing the fix. It is used in instrument procedures where a single course-reversal circuit is required for descent, alignment, or sequencing onto the next leg.
Plain English
It's a one-time loop in the shape of a holding pattern. You cross the fix, fly out, turn around, fly back, and the leg ends when you cross the fix again. One trip around — not a continuous hold.
Context Anchor
Seen in instrument procedure coding and RNAV path-and-terminator leg descriptions, especially where a procedure uses a base turn or course reversal to line the aircraft up for the next segment.
Derivation
The term 'base turn' comes from the idea of a course reversal flown over a base or anchor fix. The two-letter code HF in ARINC 424 stands for 'Hold to a Fix,' distinguishing it from HM (Hold to a Manual termination) and HA (Hold to an Altitude). Knowing the code helps because the H signals a hold-shaped path and the F signals it ends at the fix after one circuit.
Why Pilots Care
Pilots and FMS programmers need to know the leg ends after one circuit so the aircraft sequences automatically to the next leg. Confusing it with a continuous hold (HM) could leave the aircraft circling indefinitely; confusing it with a hold-to-altitude (HA) could cause early or late termination.
Analogy
Think of it like making one lap around a marked point and then leaving the lap at that point, instead of continuing around again.
Grounding Statement
The aircraft flies a shaped turn pattern once, returns to the fix, and then continues with the procedure.
Intuition Check
“Circuit” does not mean an electrical circuit here; it means one complete turn pattern. “Fix” does not mean repair; it means a named navigation point. “Base turn” here is an instrument-procedure turn, not the normal base leg in an airport traffic pattern.
Example Sentence 1
The procedure required a single circuit terminating at the fix, so the FMS flew one HF circuit and then sequenced onto the inbound approach course.
Example Sentence 2
ATC cleared the flight for the procedure that used a single circuit terminating at the fix (base turn) (HF) to establish on final.