Part 107 exam practice question · Weather & METAR
Pressure altitude corrects for non-standard pressure only. Density altitude takes that figure and corrects it further for temperature, which is why the two differ whenever the air is not at the standard temperature for that altitude. The standard temperature at sea level is 15 degrees Celsius, falling about 2 degrees per thousand feet, so at 2,000 feet pressure altitude the standard is roughly 11 degrees. At 30 degrees the air is around 19 degrees warmer than standard, and warm air is less dense, so density altitude rises well above 2,000 feet — into the neighbourhood of 4,000 feet. The consequence for a multirotor is a thinner-air performance penalty: less thrust per revolution, higher motor current, reduced climb rate, reduced effective payload and shorter endurance. Humidity adds a further small reduction in density but is not needed to answer the question, since the temperature departure alone determines the direction and most of the magnitude.
Density altitude is pressure altitude corrected for temperature, and 30 degrees Celsius is well above the roughly 11 degree standard at 2,000 feet, so the warmer, less dense air puts density altitude above 2,000 feet.
Density altitude is pressure altitude corrected for non-standard temperature. The standard lapse rate is approximately 2 degrees Celsius per thousand feet from 15 degrees at sea level. Warmer than standard air raises density altitude and degrades performance.
Hot Air Lifts the Altitude. Warmer than standard means the aircraft thinks it is higher than it is.
Standard is 15 degrees at sea level less about 2 degrees per thousand feet. That single calculation answers most density altitude questions.
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