What defines a critical engine?

The definition of a critical engine revolves around its role in maintaining the aircraft's control and performance during flight. Specifically, the critical engine is defined as the engine whose failure would result in the most significant loss of aircraft control or increase in drag.

In a multi-engine aircraft, engines are not only responsible for thrust but also for balancing the aircraft. If one engine fails and it happens to be the critical engine, this can lead to uncommanded yaw and roll due to the asymmetrical thrust being produced. This requires immediate and correct action from the pilot to maintain control and avoid potential loss of control situations.

For instance, in many twin-engine aircraft configurations, the engine that is located farthest from the aircraft's center of gravity is often critical because its failure can introduce significant yaw that the pilot must compensate for. However, this isn’t always the defining factor; it is predominantly about how greatly the loss of that engine affects control and handling characteristics.

Understanding what defines the critical engine helps pilots make informed decisions in the event of an engine failure, ensuring they can maintain control of the aircraft and respond effectively to manage the situation.