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Training and Safety Tip: What's your speed?

Ground, true, calibrated, and indicated

A common question from nonpilots and pilots alike is, “How fast will this thing fly?” In response, pilots simply quote the maximum airspeed in level flight, which is found in the pilot’s operating handbook (POH).

Photo by Mike Fizer.

But there are four speed types (indicated, calibrated, true, and groundspeed) that are important for pilots to be familiar with as they each include different factors that affect a flight.

Indicated airspeed is just what it sounds like—the speed that is displayed on the airspeed indicator. It does not factor in any variations, such as air density, temperature, or instrument error. It is simply the speed at which the aircraft moves through the air, as measured by the pitot tube and displayed by the airspeed indicator. Manufacturers use this airspeed when determining aircraft performance. It is also the airspeed air traffic controllers are interested in to help sequence aircraft and ensure aircraft comply with speed limitations within certain airspace.

Calibrated airspeed is the indicated airspeed corrected for installation error and instrument error, which are generally more pronounced at lower speeds and high angles of attack. An airspeed calibration chart, located in the POH, provides the exact amount of correction that should be factored in.

True airspeed is calibrated airspeed corrected for altitude and temperature. It’s the speed at which you move through the air, and it increases as altitude increases. You can calculate true airspeed by entering calibrated airspeed, pressure altitude, and temperature into a flight computer.

Groundspeed is true airspeed corrected for wind. It is the speed of the aircraft over the ground that your GPS displays. As headwinds increase, groundspeed will decrease. Use your flight computer to determine the groundspeed for each leg of your flight. Comparing groundspeed to true airspeed is an easy way to estimate what the winds aloft are at any point during your flight.

Review Chapter 8 of the Pilot’s Handbook of Aeronautical Knowledge for more information on airspeeds.

ASI Staff
Kathleen Vasconcelos
Kathleen Vasconcelos is an instrument-rated flight instructor and a commercial pilot with multiengine and instrument ratings. She lives in New Hampshire.
Topics: Flight School, Training and Safety, Student
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