What would indicate a loss in engine performance during flight?

Decreased RPM with no other changes is a clear indicator of a loss in engine performance during flight. RPM, or revolutions per minute, is a crucial measurement that reflects the engine's operational capacity. If RPM decreases without any other corresponding changes, such as a reduction in throttle input or a change in aerodynamic load, it suggests that the engine is not providing the expected power. This could be due to mechanical issues within the engine, fuel flow problems, or other factors affecting engine efficiency.

In contrast, a smooth flight path usually suggests that the aircraft is performing well and that the engines are operating effectively. Balancing weight on board refers to how weight is distributed within the aircraft, which is more related to handling and stability than direct engine performance. Clear weather conditions are unrelated to engine performance; they simply indicate a favorable flying environment without adverse meteorological factors affecting operations.