Density altitude

Density altitude is pressure altitude corrected for temperature: the altitude in the standard atmosphere at which the air would be this thin. Your aircraft performs to density altitude, not to what the altimeter shows.

Hot air is thin, so density altitude climbs about 118.8 ft per °C above ISA (TC AIM MET 8.4.3): DA = PA + 118.8 × (OAT − ISA temp), where OAT is the outside air temperature and ISA temp = 15 − 1.98 °C per 1000 ft (ISA, TC AIM AIR 1.5.1). Colder than ISA, density altitude drops below the pressure altitude.

Unit trap: if OAT is given in °F, convert to °C before taking the ISA deviation; feeding the Fahrenheit number straight into the rule inflates the deviation ~1.8×.

Trap: high and hot means a HIGH density altitude and worse climb, take-off, and landing. Do not read the pressure altitude straight off as the density altitude.

Practice