FAA Airline Transport Pilot (ATM)Aircraft Performance and Weight and BalanceMedium
A dispatcher is selecting a flap setting for takeoff on a runway with a close-in obstacle in the departure path. Using a greater flap extension for takeoff typically produces which combination of performance effects?
- ALonger ground roll but an improved climb gradient
- BShorter ground roll but a reduced climb gradient
- CNo change in ground roll but an improved climb gradient
- DShorter ground roll and an improved climb gradient
Show answer & explanationAnswer & explanation
Correct answer: B. Shorter ground roll but a reduced climb gradient
Greater flap extension increases lift at lower speeds, reducing takeoff ground roll, but it also increases drag, which reduces the climb gradient after liftoff. This tradeoff means the flap setting must balance the field-length-limited weight against the climb/obstacle-limited weight.
Why the other options are wrong
- A. Ground roll is shortened, not lengthened, with more flap.
- C. Climb gradient is degraded, not improved, with more flap.
- D. Climb gradient cannot improve with added drag from more flap.
Flap Setting Tradeoff
Selecting takeoff flap setting balances shorter ground roll (more flap) against better climb gradient (less flap).
- More flap = shorter roll, lower climb gradient
- Less flap = longer roll, better climb gradient
- Optimal flap setting maximizes allowable takeoff weight given runway and obstacles
Memory trick: More flap gets you off the ground fast but slows your climb to the sky.