Density Altitude and Pressure Altitude

The FAA density-altitude method turns field elevation, altimeter setting, and temperature into the performance altitude a chart is entered with. PA = elevation + (29.92 - altimeter) x 1000; ISA = 15 - 2 x (PA/1000) C; DA = PA + 120 x (OAT - ISA). A 5,000 ft field at 29.92 and 95 F is 30 C warmer than standard -> DA 8,600 ft, so lift, engine power, and prop thrust all fall as if 3,600 ft higher; a cold -5 F day drops DA to about 1,930 ft, the winter bonus. Dry-air model (humidity lowers density further); the aircraft flight manual and the pilot in command govern.

oat_c = (oat_f - 32) x 5/9; PA = elevation + (29.92 - altimeter) x 1000; ISA = 15 - 2 x (PA/1000); DA = PA + 120 x (oat_c - ISA).

FAA density-altitude method (ISA lapse correction), per FAA AC 00-6 / the ICAO Standard Atmosphere, by name; the aircraft flight manual performance charts and the pilot in command govern.

The density-altitude relation is a published FAA/ICAO standard-atmosphere approximation; the inputs come from the field elevation, the altimeter setting, and a thermometer.

Estimate. AHJ and licensed professional govern.

Field names used by the API: field_elevation_ft, altimeter_in_hg, oat_f, pa_ft, isa_c, da_ft

• Pressure altitude PA = elevation + (29.92 - altimeter) x 1000; equals the field elevation at a standard 29.92 settingFAA AC 00-6
• ISA lapse standard temperature falls 2 degrees C per 1000 ft from 15 C at sea levelICAO Standard Atmosphere
• Dry air ignores humidity, which lowers density and raises DA furtherscope of this tile