Airspeed; Why are there so many variants?

Airspeed is a very important tool for pilots. Without it, other vital information can not be calculated, which is why losing our airspeed indicator is so critical to flight safety. Let’s take a look at the few variants of airspeed and what sets them apart.

Indicated Airspeed (IAS)

First up is Indicated Airspeed. This is the most simple of them all, and it is also most used by pilots. This airspeed is read straight out of our airspeed indicator in the cockpit. This is the speed usually referred to by the manufacture for flaps, gear, and limitations speeds. It is also used for rulemaking in airspace, like 250kts below 10,000 feet or 200kts under the Bravo airspace. You can learn more about Airspace in a short video from our Two Minute Tuesday Series on Youtube. Remember, indicated airspeed is the speed the wing feels it is flying through the air.

Calibrated Airspeed (CAS)

Calibrated Airspeed is Indicated Airspeed corrected for installation errors and instrument errors. This error usually occurs when the flaps and or gear are extended. They all vary depending on the aircraft and pilot should reference the POH for the correction. Quite honestly, in the training airplanes we fly, the change is so minimal (1-2kts) that I personally don’t think it is a huge factor to consider (IAS is close enough for government work).

True Airspeed(TAS)

True Airspeed is Calibrated Airspeed corrected for nonstandard temperature and pressure. True airspeed is the reality. Pilots brag about how fast their airplane is referencing to ground speed, but the ground speed always depended on the wind. Pilots will use true airspeed when filing a flight plan.

Ground Speed (GS)

Yes we know, it is not an airspeed, it is a ground speed. In order to calculate ground speed, we must first have true airspeed and also the winds aloft. Ground speed is the speed at which the airplane is traveling over the ground, so if we have a 10kts headwind and we are flying at 100kts TAS, our groundspeed is 90kts. If we were to have a 10kts tailwind, our groundspeed would be 110kts. Ground speed is important to pilots, without taking winds into effect you could run out of fuel before you reach your destination, no matter what airplane you fly. I have experienced +150kts headwinds at altitude in a jet requiring more fuel and down to 30kts headwind in a Piper Cub causing me to go backward!

We hope this rundown on airspeeds was informative and helpful. As always, shoot us an email if you have any questions!