All aircraft have a critical engine!
The definition of a critical engine is the engine, that it failed, will have the most adverse affect on aircraft performance.
In a single engined aircraft, it's obviously that engine.
In a prop, it is the engine with a downgoing blade closest to the fuselage (unless the props are contra rotating).
In a jet (more than 2 engines), it is the outboard engine.
Crosswind will also effect the resultant performance following a failure, and thus in a twin jet, or a prop with contra rotating props, the critical engine is the upwind engine.
E.g. B747, xwind from the right, critical engine is #4.
E.g. DC10, xwind from the left, critical engine is #1.
Lancer