Which of the following factors is NOT relevant to multi-engine performance?

Passenger comfort is not directly relevant to multi-engine performance in terms of how the aircraft operates regarding its systems and performance metrics. Multi-engine performance primarily focuses on the technical aspects such as engine performance charts, weight and balance considerations, and how environmental variables like weather conditions affect the aircraft's operation.

Engine performance charts provide critical data on power output, fuel consumption, and operational limits of the engines, which are essential for calculating takeoff distances, climb rates, and overall performance. Balance is crucial, as it ensures that the aircraft is loaded correctly, which impacts controllability and stability, especially when one engine is inoperative. Weather conditions can significantly influence aircraft performance by affecting lift, drag, and control effectiveness, necessitating adjustments in operational procedures.

Passenger comfort, while important for a pleasant flying experience, does not directly impact the aircraft's performance metrics or operational safety in the same way that the other factors do.