indicated and true airspeed

[jrpilot]

What is the diffrence between indicated and true airspeed.  What do real pilots use.  


       Thank you

[Travis]

Indicated airspeed is how fast you are flying relative to the outside speed and temperature/pressure of the air going into the pitot tube.  The true airspeed is your speed relative to the ground, or Groundspeed.  The difference can be vital, since your indicated airspeed changes with your angle to the wind.  Say the windspeed is 25 kts, and you're heading into it.  Your indicated airspeed will read 25 kts FASTER than the speed you're moving over the ground.

Pilots tend to use true airspeed as their guide, since it will tell you more accurately how fast you are headed towards your destination.

At least, I think that's how it goes.

[OTTOL]

EB you DID cover it very well. Let me give you a real world scenario though JR, to put it into perspective. I flew a flight from Fort Lauderdale to Toronto and then down to Nassau today(basically the same route both directions). At FL430, my INDICATED airspeed was 220 knots, my TRUE airspeed was 440 knots, and my GROUNDSPEED was 390 knots. That was heading north. For flight planning, I took my TAS and subtracted my GROUNDSPEED, and this leaves me with a 50 knot difference. This is my crosswind component. For the flight south, I could now, very well approximate my groundspeed. If you guessed 490 knots, you were right. So,  as  a pilot, TRUE airspeed and GROUNDSPEED, are probably the most valuable numbers. Lastly, the lower you go, the smaller the difference between TRUE and INDICATED. Simply put, in smaller airplanes, it's not as big a factor.