What indicates a rapid decrease in engine power during a failure?

A rapid decrease in engine power, particularly in a turboprop engine like that of the T-6A, is primarily indicated by a rapid decay in N1 and torque. The N1 represents the rotational speed of the engine's low-pressure turbine, while torque is a measure of the engine's power output.

When an engine is operating normally, you would expect both N1 and torque to stabilize. However, in the case of an engine failure or malfunction, a sudden drop in these parameters signifies that the engine is not providing the expected thrust or power, which is critical in maintaining flight control and safety. Thus, observing a rapid decrease in these readings acts as a clear warning signal to the pilot that a significant engine problem has occurred.

Other choices, like increased ITT or fuel pressure, do not directly relate to the immediate power loss in the way N1 and torque do. ITT may rise due to abnormal combustion conditions, and increased fuel pressure might not immediately correlate to power output. Stable RPM and power do not signify a failure; they indicate normal operation, underlining that the correct choice focuses on the crucial indicators of engine performance degradation.