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How do airplanes calculate their speed?

Our pilot answers your aviation questions.

Air Canada plane

How do airplanes calculate their speed?
Philippe Dugas, Montréal

Speed relative to the air is calculated by instrument probes and sensors on the exterior of the aircraft, near the nose. These pitot tubes face the oncoming airflow (ram pressure), which is compared to static pressure to determine indicated airspeed. Computers then calculate true airspeed by factoring in such variables as temperature and pressure. Airliners also calculate Mach speed by dividing true airspeed by the speed of sound. Typical Mach cruise speeds for my airplane, the Airbus A320, is .76 to .80, which is equivalent to 76 to 80 percent of the speed of sound. 

Doug Morris
Doug Morris is an Air Canada pilot and captain on the Airbus A320. Got an aviation question? Send it to





Comments… or add another

Marjorie Watson

Thursday, June 14th 2012 09:19
You made me curious with this article, so after I've read it, I've googled about the subject and I've found another very interesting article with the Top 3 Largest Public International Airplanes ... It was a great surprise to see that one of the biggest airplanes also is one of the fastest airplane...
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