Above FL310, what is the minimum holding speed?

• A. Mach 0.70
• B. Lower of Mach 0.70 or drift-down speed
• C. Drift-down speed
• D. Mach 0.75

Answer: (B)

At high altitudes, speed is governed by Mach rather than indicated airspeed, and you must stay within the aircraft’s safe envelope while keeping margin to stall. For holds above FL310, the minimum holding speed is defined as the lower of Mach 0.70 or the drift-down speed. This means you pick whichever is smaller to ensure you won’t hold too slow to remain controllable in a descent (drift-down) and you won’t exceed the Mach limit if that’s the tighter constraint. If drift-down speed is lower than Mach 0.70, that lower value governs; if drift-down is higher, Mach 0.70 governs. The other choices fail to account for this conditional limit that adapts to weight, configuration, and engine-out performance.