45. Which combination of atmospheric conditions will reduce aircraft takeoff and climb performance?
C) High temperature, high relative humidity, and high density altitude.
HHH is a pilot's nemesis. Any one of them is bad for aircraft performance: Hot, humid or High (altitude). All of these conditions reduce the volume of air molecules for the wings and propellers to bite.
From: FAA-H-8083-25B "Pilot's Handbook of Aeronautical Knowledge"
"Conditions that affect takeoff and climb performance, such as high elevations, high temperatures, and high humidity (high density altitudes), may require a reduction in weight before flight is attempted.
Increasing the temperature decreases the density. Conversely, decreasing the temperature increases the density. Thus, the density of air varies inversely with temperature. Water vapor is lighter than air; consequently, moist air is lighter than dry air. Therefore, as the water content of the air increases, the air becomes less dense, increasing density altitude and decreasing performance."
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