Which factor contributes to increased required takeoff distance?

Increased required takeoff distance is significantly influenced by a tailwind. When an aircraft takes off into a tailwind, the effective airspeed at which the aircraft must reach for takeoff is higher, as the wind pushes the aircraft forward, reducing the relative wind speed over the wings. This means that the aircraft may not achieve the necessary lift at the same point on the runway as it would without the assistance of a headwind. Consequently, to reach the required airspeed for takeoff, the aircraft may need a longer runway distance.

Considering the other factors, headwinds actually decrease the required takeoff distance because they provide additional lift and allow the aircraft to reach the necessary airspeed more quickly. Clear runway conditions generally support optimal takeoff performance, allowing for max effective engine performance and braking. Lower aircraft weight would also lead to a reduction in takeoff distance, as lighter aircraft require less distance to achieve the required airspeed for takeoff. Thus, a tailwind is the primary factor that increases the required takeoff distance.