Which of the following is not a key factor affecting aircraft performance?

Aircraft performance is influenced by several key factors, including weight, altitude, and temperature. Each of these components significantly impacts how an aircraft operates.

Weight affects an aircraft's lift-to-drag ratio, fuel efficiency, and overall performance during takeoff and landing. An increase in weight generally requires a longer takeoff distance and can affect climb rate and maneuverability.

Altitude is crucial as it dictates the air density. As altitude increases, air becomes less dense, which can reduce lift generated by the wings as well as the performance of the engines. This necessitates adjustments in flight planning and operations.

Temperature also plays a vital role in aircraft performance. Higher temperatures lead to lower air density, thereby affecting lift and engine performance. Conversely, cooler temperatures enhance both lift and engine efficiency.

In contrast, the length of flight does not inherently influence the performance characteristics of an aircraft in the same way. While longer flights may have implications on fuel burn and operational planning, they do not directly alter the performance metrics connected to weight, altitude, or temperature during a specific flight. Thus, it stands apart as a less relevant factor concerning the key performance determinants of an aircraft.