What is the difference between tas cas and ias

True airspeed is the speed of your aircraft relative to the air it's flying through. As you climb, true airspeed is higher than your indicated airspeed. Pressure decreases with higher altitudes, so for any given true airspeed, as you climb, fewer and fewer air molecules will enter the pitot tube. Because of that, indicated airspeed will be less than true airspeed. Many aircraft, such as those with gas turbine engines, can reach a higher TAS at higher altitudes because their engines are more efficient at higher altitudes.

The movement of your airplane relative to the ground is called groundspeed. It's true airspeed corrected for wind. With a true airspeed of knots and a tailwind of 20 knots, you'd be flying a groundspeed of knots. If you shot a police radar gun at a plane flying by, you'd be measuring groundspeed of the airplane, assuming the officer was stationary. Calibrated airspeed is indicated airspeed corrected for instrument and positional errors. At certain airspeeds and with certain flap settings, the installation and instrument errors may total several knots.

This error is generally greatest at low airspeeds, with nose high pitch attitudes. If there is no wind it is also the same as ground speed. Want to learn more about how your airspeed indicator works? Click here. Become a better pilot. Subscribe to get the latest videos, articles, and quizzes that make you a smarter, safer pilot.

To: Separate email addresses with commas. Calibrated airspeed is the same as true airspeed when you are flying at sea level under International Standard Atmosphere ISA conditions. Because air density decreases with an increase in altitude, an aircraft has to be flown faster at higher altitudes to cause the same pressure difference between pitot impact pressure and static pressure. A pilot can find TAS by two methods. The most accurate method is to use a conventional or electronic flight computer.

A second method, which is a rule of thumb, provides the approximate TAS. Simply add 2 percent to the CAS for each 1, feet of altitude. Groundspeed is the actual speed of the airplane over the ground.

While not an airspeed, GS is important for navigation and has a major impact on the time it takes to get to a destination. It is also the airspeed at sea level in the International Standard Atmosphere at which the dynamic pressure is the same as the dynamic pressure at the True Airspeed TAS and altitude at which the aircraft is flying.

Pilot Institute may earn commission from sales that happen when you click on links. We are a member of the Amazon Affiliate Program. Subscribe now and get a weekly video sent to your inbox on various drone topics hosted by Greg. Sign me up for the newsletter! Blog Exclusive articles on drones and airplanes. Go to blog home. There are numerous ways to measure your airspeed. We talk about 6 different ways below: 1.

Indicated Airspeed IAS The direct instrument reading obtained from the Airspeed Indicator ASI , uncorrected for variations in atmospheric density, installation error, or instrument error.