When is true airspeed equal to groundspeed?

True airspeed and groundspeed are equal when an aircraft is flying in calm air, meaning that there is no wind affecting the aircraft's motion. True airspeed is the speed of the aircraft relative to the surrounding air, while groundspeed is the speed of the aircraft relative to the ground. In calm conditions, there are no wind components to influence the aircraft’s movement; thus, the airspeed and groundspeed will be the same.

In scenarios where there are winds—whether headwinds or tailwinds—the relationship between true airspeed and groundspeed changes. A headwind would slow the groundspeed compared to the true airspeed, while a tailwind would increase the groundspeed. Turbulent air can cause fluctuations in both true airspeed and groundspeed but does not inherently make them equal. During descent, similar principles apply; unless there are no wind currents, the true airspeed would not necessarily equal groundspeed.