A remote PIC is planning a flight at a site with an elevation of 2,000 ft MSL. The reported temperature is 95°F and the altimeter setting is 29.92. This combination of conditions is most likely to result in which of the following compared to a standard day?

Density altitude is pressure altitude corrected for non-standard temperature, and it is the altitude the aircraft actually behaves as though it is flying at. Three factors thin the air: elevation, heat and humidity. Here two of them are working together — a 2,000-foot field and 95°F, well above the roughly 52°F standard temperature at that elevation — so the density altitude is far higher than the field elevation. Thin air gives the propellers less mass to accelerate, so each rotation produces less thrust, and the motors compensate by drawing more current. The practical consequences for a small unmanned aircraft are reduced climb rate, longer response to control input, shorter endurance and less margin in an aborted descent.

High elevation combined with a temperature far above standard produces a density altitude well above the published field elevation. Thinner air reduces the thrust each propeller revolution generates, so propeller efficiency falls and performance degrades across the board.

Standard conditions are 59°F at sea level with a lapse rate of about 3.5°F per thousand feet, and 29.92 inches of mercury. Density altitude rises with elevation, temperature and humidity, and rising density altitude degrades propeller thrust, climb performance and endurance.

High, Hot and Humid all push density altitude up and performance down. Thin air means the propeller has less to bite.

An altimeter setting of 29.92 tells you pressure is standard, which isolates temperature as the variable. That is a hint the question is testing the temperature effect specifically.

• •Believing heat lowers density altitude
• •Assuming field elevation and density altitude match whenever pressure is standard
• •Overlooking that reduced performance affects climb and abort margin, not just endurance