True airspeed is calculated by correcting equivalent airspeed for what type of variation?

True airspeed is derived from equivalent airspeed by correcting for air-density variation from standard conditions. Equivalent airspeed is defined as the calibrated airspeed adjusted for instrument and position errors. It represents a specific energy state of the aircraft, assuming standard atmospheric conditions at sea level.

As altitude increases, the air density decreases. To convert equivalent airspeed to true airspeed, you must account for this decrease in air density since true airspeed represents the actual speed of the aircraft relative to undisturbed air at the aircraft's current altitude and temperature. This correction ensures that the true airspeed reflects the actual conditions affecting the aircraft's performance and aerodynamic characteristics.

In contrast, while temperature variation from standard conditions can influence performance, it is not the primary factor in converting equivalent airspeed to true airspeed. Similarly, pressure variation is related to altitude changes but does not represent the direct correction required, and wind variation pertains to the speed relative to the ground rather than the air itself.