Mach Trim begins to operate at 0.4 Mach and is operable in both manual and autopilot flight operations.

• A. True
• B. False — it does not operate when the autopilot is engaged
• C. It operates only in manual flight
• D. It operates only in autopilot flight

Answer: (B)

Mach Trim is designed to start working at about 0.4 Mach to counteract the trim changes caused by increasing speed and Mach effects. The statement says it operates in both manual and autopilot flight. In this system, however, Mach Trim does not operate when the autopilot is engaged, so it cannot function under autopilot control. This setup prevents conflicting trim commands between the pilot’s inputs and the autopilot’s control. Therefore the claim is false: Mach Trim is available in manual flight, but is disabled once the autopilot is engaged.