What should be done if N2 is 57% or less at an OAT of -20°C or warmer?

When N2 is 57% or less at an outside air temperature (OAT) of -20°C or warmer, it is critical to maintain safe operating parameters for the engine. The correct action in this scenario is to not exceed idle acceleration. This guideline ensures that the engine remains within safe limits during the takeoff roll, preventing potential engine failure or other performance issues that could arise from exceeding safe operating parameters.

If N2 is too low, it indicates that the engine may not be producing sufficient thrust for a safe takeoff. By adhering to the protocol of not exceeding idle acceleration, the crew can avoid pushing the engine beyond its limits, which could lead to a failure or loss of control during the critical phases of flight, particularly takeoff.

Other options, such as initiating takeoff or continuing to accelerate above idle, could result in unsafe conditions, as they would involve attempting to take off with inadequate engine performance. Performing an emergency landing is not appropriate in this situation since the issue is related to takeoff limitations and not an immediate in-flight emergency. Thus, the decision to limit acceleration to idle is crucial for maintaining safety in these specific operating conditions.