Critical engine

The critical engine of a multi-engine, fixed-wing aircraft is the engine whose failure would most adversely affect the performance or handling abilities of an aircraft(§1.1). On propeller aircraft, there is a difference in the remaining yawing moments after failure of the left or the right (outboard) engine when all propellers rotate in the same direction due to the P-factor. On turbojet/ turbofan aircraft, there usually is no difference between the yawing moments after failure of a left or right (outboard) engine.