Definition
A correction value, expressed in feet, that is added to or subtracted from the field elevation (indicated altitude) to obtain pressure altitude when the altimeter setting differs from the standard 29.92 inches of mercury. The factor accounts for the deviation of the current altimeter setting from standard atmospheric pressure.
Plain English
A small adjustment in feet that you apply to your airport's elevation to find pressure altitude when the day's pressure isn't standard. If pressure is higher than standard, you subtract feet; if lower, you add feet.
Context Anchor
Seen on density altitude charts when converting field elevation and altimeter setting into pressure altitude before finding density altitude.
Why Pilots Care
Density altitude directly affects takeoff distance, climb rate, and engine performance; using the correct conversion factor prevents underestimating how the airplane will actually perform.
Grounding Statement
On a low-pressure day, the airplane performs as if the airport were higher than its actual elevation; on a high-pressure day, it performs as if the airport were lower.
Intuition Check
Do not read “factor” as a general reason or cause here. In this chart, it means a specific plus-or-minus number of feet used to adjust field elevation to pressure altitude.
Example Sentence 1
With an altimeter setting of 30.22, the chart gave a pressure altitude conversion factor of -279 feet, which we subtracted from the field elevation before entering the performance table.
Example Sentence 2
With a high temperature, the conversion factor increased, showing that the density altitude was several thousand feet above the field elevation.