Which factor does NOT affect the aircraft's performance at high altitudes?

The wing surface area does not significantly affect an aircraft's performance at high altitudes in the same way that air density, engine efficiency, and temperature do.

At higher altitudes, the air density decreases, which directly impacts the lift generated by the wings. With lower air density, an aircraft requires a higher speed or larger wing area to generate sufficient lift for takeoff and sustained flight. Engine efficiency is also influenced by altitude; engines may produce less thrust in thinner air, affecting overall performance and climb capability. Likewise, temperature plays an important role at altitude, as it can affect both air density and engine performance.

While wing surface area can play a role in aircraft design and overall lift characteristics, it remains constant once the aircraft is built. In contrast, the factors of air density, engine efficiency, and temperature vary with altitude, directly impacting performance during flight. Hence, wing surface area stands out as the factor that does not dynamically affect performance relative to those critical altitude-dependent conditions.