What is an indication of engine failure during cruise flight?

The indication of engine failure during cruise flight is typically a loss of instrument readings. When an engine fails, you may notice abnormal readings on the engine instruments, including reduced RPM in the affected engine, fluctuations in oil pressure, or other primary flight data being affected. The loss of instrument readings signifies that the engine is not operating as expected, which can serve as an early warning sign for pilot intervention.

In contrast, an increase in RPM might suggest that the other engine is compensating for the loss of power, and a stable flight attitude would generally indicate that the aircraft is behaving normally under current conditions, which does not suggest an engine failure. A decrease in altitude can occur for various reasons, such as changes in weight, but is not specifically indicative of engine failure since other factors could cause altitude loss as well.