Which of the following is NOT a method to disconnect the autopilot?

The correct answer highlights that the engine fire push button is not a method to disconnect the autopilot. Each of the other options—red buttons on yokes, AP ENG on the Flight Control Panel (FCP), and AP DISC on the FCP—are specifically designed or designated for the purpose of disengaging the autopilot system.

The red buttons on the yokes are typically known as 'autopilot disconnect' buttons, allowing pilots to manually override the autopilot quickly in emergency situations or when they want to take manual control of the aircraft. The AP ENG button on the FCP is used to engage or disengage the autopilot system's functions. Similarly, the AP DISC button is explicitly meant for disconnecting the autopilot when needed.

In contrast, the engine fire push button serves a completely different function; it is intended for emergency situations related to engine failure or fire, ensuring that the engine can be shut down or controlled appropriately. Thus, it does not relate to autopilot disconnection and confirms why this option is the correct choice as the one that does not belong in the context of disconnecting the autopilot.