Which factor most directly increases takeoff distance?

• A. Decrease in outside air temperature
• B. Increase in density altitude (thinner air)
• C. Increase in wing area
• D. Reduction in gross weight

Answer: (B)

Takeoff distance is strongly tied to air density because lift and thrust come from how thick the air is. When density altitude increases, the air is thinner. That means the wing must move faster through the air to generate the same amount of lift, and the engines produce less thrust. With less lift and thrust available at any given speed, you have to accelerate longer to reach the speed at which the airplane can leave the runway, so the takeoff distance grows directly with density altitude.

Cooling the air lowers density altitude, giving thicker air, more lift, and more thrust, which shortens the required runway. Increasing wing area adds more lift for a given speed, so you reach takeoff lift sooner and need less runway. Reducing gross weight lowers the lift required to take off and reduces thrust needs as well, also shortening the distance.