What is the difference between true/indicated airspeed?
From FlightSim
Q:
First what should I use. True airspeed or Indicated airspeed? In FS98 I always used Indicated airspeed. Problem is this, When flying a B757 I should be able to reach minimum of 450-500knots, right? Why does the maximum speed indicator decrease as I gain altitude.. As I approach 23000 feet the max speed drops. By the time I reach 25000 I can only fly 300 knots without an overspeed indication. What causes the drop in airspeed as you climb? I climb at thesuggested 1800-2000
A:
As you gain altitude, the air becomes less dense. With less airmolecules entering the pitot tube (routes air to the airspeed indicator) the indicated airspeed will read lower, but your over the ground speed will be muchhigher, unless your fighting major headwinds. Compare your GPS ground speed with your indicated speed. If you were to land an aircraft at a higher altitude airport such as Evanston, Wyoming which is over 7,000 msl altitude, & flew downwind for landing at 90 knots, you would actually be covering more ground than you would at a sea level airport doing 90 kias. Your pattern would actually be larger&the runways are usually longer to make up for this.
