There are two methods an autopilot can function in GA. What are they?

• A. Position based - relation to horizon
• B. Rate based - relation to TC
• C. Position based - relation to horizon; Rate based - relation to TC
• D. Attitude hold and altitude hold

Answer: (C)

Autopilots in GA fly in two fundamental control modes: attitude (position) control and rate control. In attitude control, the autopilot uses the horizon reference to hold a specific pitch and bank, effectively maintaining a chosen orientation relative to the sky. It commands the surfaces to keep that attitude, so the airplane tracks a steady flight path despite small disturbances. In rate control, the autopilot relies on the turn coordinator to maintain a set rate of turn about the vertical axis. Instead of fixing the attitude, it adjusts bank to keep the turn happening at the commanded rate, which is handy for standard-rate turns and coordinated flight. Altitude hold is a separate function and not part of these two ways the autopilot governs orientation or turn rate, so the two methods GA autopilots commonly use are attitude control relative to the horizon and rate control relative to the turn coordinator.