What's the Difference Between Airspeed and Ground Speed?

airplane graphic — Airspeed and ground speed are completely different when it comes to determining how fast an airplane flies.Greg Bajor/Getty Images

Back in February 2019, a Virgin AtlanticBoeing787年宾夕法尼亚州飞机飞过route from Los Angeles to London reached what might seem like an amazing speed of 801 miles per hour (1,289 kilometers per hour), according toCBS News.

But the speed record wasn't because that Virgin Atlantic aircraft itself was exceptionally fast. Like a sprinter running with the wind at his back, the aircraft benefited from an exceptionally fastjet stream, a high-speed wind moving at 231 miles per hour (371.7 kilometers per hour). It was the fastest jet stream in more than 60 years.

As CBS News explained, the result was that the 787 flew considerably faster than the aircraft's typical cruising speed of 561 miles per hour (902.8 kilometers per hour).

Therein lies the difference between airspeed and ground speed.

Asthis explaineron the NASA website details, ground speed is how fast an airplane is traveling, relative to a fixed point on the ground. Think of it this way: Ground speed is how fast an airplane's shadow would move across the land. If there's a strong wind pushing an aircraft, that's reflected in the ground speed.

Airspeed, in contrast, is how fast an airplane is really flying strictly under its own power, which is calculated by subtracting the wind speed from the ground speed.NASA explains:

On a perfectly still day, the airspeed is equal to the ground speed. But if the wind is blowing in the same direction that the aircraft is moving, the airspeed will be less than the ground speed.

Airspeed doesn't just affect airplanes. It also affects our vehicles on the ground. As thisstudypublished in 2013 in the International Journal of Energy and Environmental Engineering describes, a car's airspeed on the highway is what really determines itsfuel efficiency, rather than ground speed or the speedometer reading.