← All explained questions · Weight, Balance and Aircraft Performance
How does high humidity affect aircraft performance?
Choices
It increases air density and improves climb
Water vapor makes air less dense, not more.
✓ It decreases air density and degrades performancecorrect
Water vapor is lighter than dry air, so humid air is less dense and reduces performance.
It has no measurable effect
Humidity does reduce air density and engine power.
It only affects turbine engines
Humidity affects piston aircraft performance as well.
Why
Humid air is less dense than dry air because water vapor weighs less than the air it displaces, so high humidity raises density altitude and reduces lift, thrust, and power.
FAA source: FAA-H-8083-25 (performance)browse the reference library →
Original study question written for this course — representative of FAA knowledge-test topics, not an actual current FAA exam question.