Above FL350, climb at no less than Mach what?

• A. Mach 0.70
• B. Mach 0.74
• C. Mach 0.78
• D. Mach 0.80

Answer: (B)

Above high-altitude flight, speeds are governed by Mach rather than indicated airspeed because air density is so thin that engine performance and aerodynamic margins are more reliably managed by Mach. A minimum Mach is published for climbs above a certain altitude to ensure you maintain a safe climb gradient and proper engine operation as you rise into thinner air. The required minimum is the middle option, which means you must not descend below that Mach value above FL350. The slower option would fail to meet the mandated climb performance, while the faster options are merely above the minimum and not required unless conditions demand it. In short, the procedure sets a minimum Mach to guarantee safe, efficient climb, with the middle value being the threshold.