* Malfunctions: Problems with the engine's components (e.g., fuel system, air intake, ignition system, turbocharger) can restrict power output.
* Limiting systems: The engine's computer system might intentionally reduce power to prevent damage, such as overheating, or due to sensor readings indicating a problem (e.g., low oil pressure).
* Operational conditions: Factors like high altitude, extreme temperatures, or low-quality fuel can also cause reduced power.
* Maintenance: Neglected maintenance (e.g., dirty air filter, worn spark plugs) can lead to decreased performance.
Essentially, it signifies a problem that needs attention. The severity varies greatly; it could be a minor temporary issue, or a serious problem requiring immediate repair. In the case of aircraft, it can be a critical situation requiring immediate action.
