Airspeeds Every Pilot Should Know

The Four Basic Types of Airspeed.

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Indicated Airspeed (IAS)

Indicated airspeed is the speed that the pilot reads directly from the instrument gauge. When the POH references airspeed, it usually is referencing indicated airspeed unless it states otherwise. Indicated airspeed is not corrected for air density, installation error, or instrument error.

Calibrated Airspeed (CAS)

Calibrated airspeed is airspeed corrected for instrument error and installation error. This error is generally greater at lower airspeeds, manufacturers try their best to keep error at a minimum; however, it is impossible to eliminate all errors. In the R44 POH there is multiple charts for translating indicated airspeed to calibrated airspeed. Depending on what equipment your aircraft is has, use that specific chart. For example, a R44 with a heated pitot tube or floats will have a separate calibrated airspeed chart.

R44 Cadet POH 9-6.3

True Airspeed (TAS)

True airspeed is calibrated airspeed corrected for altitude and non-standard temperature. Air density decreases with altitude. For a given calibrated airspeed, as altitude increases true airspeed will also increase. The most accurate way of calculating true airspeed is with an E6-B flight computer. First you need to calculate the Pressure altitude for the altitude you plan on flying, next using the altitude correction window on your flight computer, set that pressure altitude against the temperature for that altitude. Read TAS on the outer ring and CAS on the inner ring. TAS is used for flight planning and when filling a flight plan.

Ground speed (GS)

Ground speed is the actual airspeed of the helicopter over the ground. Ground speed is true airspeed corrected for wind. Whenever calculating ETE (estimated time enroute) and when fuel planning, use ground speed.