FAA Airline Transport Pilot (ATM)Navigation, Air Traffic Control and ProceduresMedium
Two aircraft are assigned the same oceanic track and altitude using the Mach Number Technique. The leading aircraft is assigned Mach .82, and the trailing aircraft is assigned Mach .80, with 10 minutes of longitudinal separation established at the oceanic entry point. What will happen to this separation over the course of the crossing?
- AIt becomes irrelevant once above FL350
- BIt will remain exactly 10 minutes throughout the crossing
- CIt will decrease, risking a loss of separation
- DIt will increase because the leading aircraft is faster
Show answer & explanationAnswer & explanation
Correct answer: D. It will increase because the leading aircraft is faster
Under the Mach Number Technique, aircraft maintain assigned Mach numbers to preserve separation. Since the leading aircraft is faster (Mach .82) than the trailing aircraft (Mach .80), the leading aircraft will gradually pull away, increasing the longitudinal separation over time.
Why the other options are wrong
- A. Mach technique separation standards apply regardless of specific altitude within the oceanic structure.
- B. Separation only stays constant if both aircraft maintain identical Mach numbers.
- C. Separation would decrease only if the trailing aircraft were faster, which is not the case here.
Mach Number Technique
A longitudinal separation method used in oceanic airspace where aircraft on the same track and altitude are assigned specific Mach numbers to maintain or adjust spacing over time.
- Used primarily in non-radar oceanic airspace
- Aircraft must maintain assigned Mach number unless ATC approves a change
- Speed differences between aircraft change the separation over time
- Any Mach number deviation requires prior ATC clearance
Memory trick: 'Faster in front, gap grows — Mach math tells the tale.'