What defines a critical engine in aviation?

In aviation, the concept of a critical engine refers to the engine whose failure would have the most significant negative impact on the aircraft's performance and handling characteristics. This is especially relevant in multi-engine airplanes, where the loss of one engine can affect the aircraft's ability to maintain controlled flight.

The critical engine is often determined by the specific design and performance attributes of the aircraft. For example, in certain configurations, the failure of one engine might lead to a significant yawing motion and loss of lift on one side, thereby complicating pilot response and potentially leading to a dangerous situation. Understanding which engine is critical helps pilots and engineers design safety measures and response protocols, ensuring that operations can continue safely, even in the event of an engine failure.

In this context, while factors like thrust output, likelihood of failure, and maintenance needs are all important considerations, they do not directly define what makes an engine "critical" in terms of performance impact. The critical engine is focused on how its failure will compromise the aircraft's controllability and safety during flight.