What happens when the aircraft climbs to the attitude where the throttle is fully opened by the servo to maintain the MAP selected?

• A. The MAP automatically increases as altitude increases.
• B. The throttle remains fixed and MAP drifts with altitude.
• C. The MAP is maintained at the selected value by the servo as the aircraft climbs.
• D. The engine power is reduced to hold MAP constant.

Answer: (C)

The key idea is that a servo-controlled throttle is designed to hold a chosen manifold pressure (MAP) constant as the airplane changes altitude. As you climb, ambient pressure falls, so more throttle is needed to keep that same MAP. The servo automatically moves the throttle to achieve the selected MAP. If the climb brings you to a point where the throttle is already at full open, the servo will stay at maximum to preserve the MAP as long as it can; the MAP remains at the chosen value while possible. If you could not supply enough pressure even at full throttle, the MAP would no longer be maintainable, but within the operating range the servo keeps the MAP constant.