I have a "general" idea on the difference between ISA and TAS and Ground Speed (obvious), but I was wondering if someone could explain in simple terms the difference amd relation between them.Also - if you're on a roll - the difference between TAT and SAT would be great too.Thanks,BobKMEM

GS - speed of your aircraft in relation to groundTAS - speed of your aircraft in relation to airIAS - speed as indicated directly by the pitot tube (not corrected for temperature or air density).Michael J.http://www.reality-xp.com/community/nr/rsc/rxp-higher.jpg

Let's not forget about poor 'ol CAS either! ;-)Regards,http://www.dreamfleet2000.com/gfx/images/F...RUM_LOUF_A2.jpg

and the ISO, DIN, ASA, NEN, FAA, CAA, JAA :-rotor

Just to add a more complete list :)EAS - Equivelent airspeed. The speed the a/c thinks it is flying at. By that I mean for the a certain amount of lift to be generated a certain number of air particals have to be accelerated over the wing, so as density decreases with altitude the a/c has to fly faster to make up for the deficit to prevent a stall. As TAS increases to beyond 300kts(ish) the air in the pitot is compressed and will thus show a higher reading of IAS than the EAS. Therefore as Altitude increases the indicated stalling speed increases...but the a/c will always stall at the same EAS.IAS - Indicated Air Speed. Relevent for old or light a/c.CAS - Calibrated Airspeed. This is IAS corrected for instrument error and also the error induced by the positioning of the Pitot (it is never perfect, but predictable).RAS - Rectified Airspeed. This is the same as CAS.TAS - True Airspeed. This, unlike EAS, IAS, CAS and RAS is not related to the density of the air. At sea level TAS = CAS, below sea level CAS > TAS at altitude CAS < TAS.Not forgetting Mach wich is expressed as a decimal (M.75 for example). Mach Number = (Pitot Pressure + Static Pressure) / Static Pressure or Mach No = TAS/LSS where LSS = Local Speed of Sound = 38.94 * SQRT(Air Temp in Kelvins). Basically, this means that as the temprature drops, so the LSS decreases. As it decreases, then for the same TAS your Mach No increases. So as you climb Mach No increases more than TAS.GS - Ground Speed. In still air GS = TAS. With a tailwind GS > TAS and with a headwind GS < TAS.