To where does a critical engine apply in modern aircraft?

• A. Turboprop only
• B. Turbofan only
• C. Jet engine only
• D. Piston engine

Answer: (A)

In multi-engine flight, you look at which engine’s failure would cause the biggest loss of directional control. That engine is the critical engine. The reason this matters here is that with propeller-driven powerplants, losing one engine changes not only thrust but also the way the propeller wash and the engine’s thrust interact with the air around the fuselage. Those propeller-related effects—like slipstream impact and P-factor—tend to produce a stronger yaw and more challenging handling when one engine quits than in other propulsion setups.

Turboprop aircraft are the modern example of propeller-driven engines, so the critical-engine concept is most clearly applied there. Jets (turbofan/jets) don’t rely on propeller wash in the same way, and while engine-out performance is still important, the traditional critical-engine analysis isn’t the same focus. Piston-engine twins exist, but in the context of “where does the critical engine apply” in modern practice, turboprop is the best fit among the options.