CFI Pop Quiz #303 - Humidity

[Chris Burgess]

If the atmospheric pressure and temperature remain the same, how would an increase in humidity affect takeoff performance?

A) Longer takeoff distance; the air is more dense.
B) Longer takeoff distance; the air is less dense.
C) Shorter takeoff distance; the air is more dense.

[Caribean_gyro]

i WILL SAY A.

[EI-GYRO]

B. Water vapour (H20) is less dense than air so high humidity lowers density,
hence longer takeoff distance..

[Paul_Zurawski]

Performance figures are based on dry air...adding water vapor will reduce the air molecules in that cubic foot...less dense..(B)

[ventana7]

BBBB

Rob

[Chris Burgess]

"B" is most correct. If the atmospheric pressure and temperature remain the same, how would an increase in humidity affect takeoff performance? (B) Longer takeoff distance; the air is less dense.

Density altitude is the altitude in standard air where the density is the same as the existing density. It is determined by the pressure, temperature, and moisture content of the air. Since water vapor is less dense than dry air, an increase in humidity, with atmospheric pressure and temperature remaining the same, will increase the density altitude and require a longer takeoff distance. Reference FAA-H-8083-25

[JByrd]

B. Clear answer.

Jim