What is the difference between AP1 and AP2 autopilots and how can they be used in abnormal situations?

• A. AP1 and AP2 are identical and always operate together.
• B. AP1 and AP2 are independent autopilots; either can control the aircraft; select the remaining unit if the other is failed and cross-check with FD.
• C. AP1 controls autopilot while AP2 controls flight director only.
• D. AP2 is for takeoff only.

Answer: (B)

AP1 and AP2 provide redundancy by offering two independent autopilot channels, each capable of commanding the aircraft. In normal operation either one or both can control the airplane, and you can switch to the functioning autopilot if one channel fails while continuing to follow the Flight Director’s guidance for verification. In an abnormal situation, you select the remaining autopilot to maintain automated control and rely on the Flight Director as a cross-check to ensure the aircraft is following the desired path. The autopilots are not limited to a single role or phase; AP2 does not control flight director only, and both units can be used together or separately depending on the situation.