FAA Private Pilot Airplane (PAR)Performance, Weight and BalanceEasy
An aircraft is experiencing a higher-than-normal ground roll during takeoff, despite no changes in gross weight or wind conditions. Which atmospheric condition is most likely contributing to this increased ground roll?
- ADecreased ambient air temperature
- BIncreased humidity at sea level
- CHigher-than-standard atmospheric pressure
- DLower-than-standard atmospheric pressure
Show answer & explanationAnswer & explanation
Correct answer: D. Lower-than-standard atmospheric pressure
Lower-than-standard atmospheric pressure reduces air density. Reduced air density means the wings produce less lift and the propeller produces less thrust at a given true airspeed, requiring a longer ground roll for takeoff.
Why the other options are wrong
- A. Incorrect. Decreased temperature increases air density, which would improve performance and shorten ground roll.
- B. Incorrect. Increased humidity does slightly decrease air density, but lower pressure has a more significant impact and is a direct cause of reduced performance.
- C. Incorrect. Higher pressure increases air density, which would improve performance and shorten ground roll.
Pressure Altitude Effects
Pressure altitude is the altitude in the standard atmosphere corresponding to a particular pressure. Lower-than-standard pressure results in a higher pressure altitude, which negatively impacts aircraft performance.
- Lower pressure = higher pressure altitude
- Higher pressure altitude reduces engine power and wing lift
- Results in longer takeoff/landing distances and reduced climb rate
Memory trick: Pressure Low, Performance Slow