Under what conditions does the automatic APR activate?

The automatic APR (Alternate Power Reserve) activates under specific conditions mainly focusing on aircraft safety and engine performance. When the APR switch is turned ON, the thrust levers are in the TO (Takeoff) detent, and N2 (the rotational speed of the engine's low-pressure compressor) differs by 15%, it indicates a significant performance discrepancy between the engines. This condition prompts the system to activate the APR to provide additional thrust to compensate for any power loss or imbalance between the engines, ensuring a safe and effective takeoff.

This scenario reflects a situation where one engine is not performing as expected, and by activating the APR, the aircraft can maintain adequate performance during critical phases of flight. This condition is particularly crucial during takeoff where maximum thrust is essential for a successful climb-out and overall safety.

In contrast, the other options describe scenarios that do not align with the conditions necessary for APR activation. For instance, with the APR switch OFF, or with thrust levers in CL (Climb) detent, or a single engine in operation without the appropriate conditions, the system would not engage, as those states either lack a need for additional thrust or undermine the parameters needed for activation. Therefore, only the condition listed fosters the appropriate environment for