rambling thoughts...
Unless otherwise noted, speeds on charts are IAS. The pitot is going to reference the airspeed for performance, if the pitot has 220kts airspeed, so does the wing, and airspeed generates lift/drag. Aircraft CAT A,B, C, etc final approach speeds are performance based, hence IAS.
Remember that charts were made for aircraft that dont have GPS or accurate method to determine ground speed. (ever hear a Cessna 150 ask ATC for a groundspeed check?)
Distances on charts are used for ground speed reference. (ATC uses ground speed for airspace separation.) as an example, if you need DME 1 or DME 5, you need groundspeed....
Time references on charts are based on GS, so circling and hold patterns.
When one needs to calc climb gradients, such as 200'/nm, one must use groundspeed as this is a distance...speed on SID will only be ref for airspace restrictions.
The assumptions are that the aircraft is always taking off into the wind, as this generates the lowest groundspeed, and hence a shorter takeoff length. So depending on winds, the takeoff distance may be shorter/longer. The 200'/nm CG is based on crossing the runway end at 35'.
JT is correct, with GPS navigation, ground speed is becoming more prevalent as a very useful tool, especially with NextGen trajectory optimization, as velocity is a vector based determination.
Last edited by FlightPathOBN; 27th Apr 2011 at 21:36.