FAA Private Pilot Airplane (PAR)Performance, Weight and BalanceEasy
As density altitude increases on a hot day at a high-elevation airport, what combination of effects should a pilot expect during takeoff?
- ADecreased engine power, decreased propeller thrust, and reduced lift, resulting in a longer takeoff roll
- BNo change in engine power, but a shorter takeoff roll due to thinner air
- CIncreased lift due to less dense air, resulting in a shorter takeoff roll
- DIncreased engine power, increased propeller thrust, and a shorter takeoff roll
Show answer & explanationAnswer & explanation
Correct answer: A. Decreased engine power, decreased propeller thrust, and reduced lift, resulting in a longer takeoff roll
Thinner air at high density altitude reduces the mass of air available for combustion (less engine power), reduces propeller thrust efficiency, and reduces lift for a given airspeed. All three factors combine to lengthen the takeoff roll and reduce climb performance.
Why the other options are wrong
- B. Engine power does decrease, and takeoff roll increases, not decreases.
- C. Less dense air reduces, not increases, lift for a given speed.
- D. This is the opposite of what actually happens in less dense air.
High Density Altitude Effects
High density altitude reduces engine power, propeller efficiency, and lift, all of which degrade takeoff and climb performance.
- Less dense air = less oxygen for combustion
- Propeller bites less air, producing less thrust
- Wings need higher true airspeed to generate the same lift
Memory trick: Thin air steals your power, thrust, and lift.