Originally Posted by
wideman
Agree with henry999 that the GCM is useful only for a general idea of validity. The difference between the *A and GCM mileages can be huge -- probably as much as 100 miles or more on a complete trip. I do have to use the GCM figure for surface segments that *A doesn't fly, but haven't run into trouble with that ... yet.
The *A RTWMC is usually very close to the numbers in Amadeus, much more reliable than the GCM, except of course for direct flights with a stop where it always calculates the point to point mileage rather than the nonstop distance. The *A RTWMC does include surface sectors in the total mileage, but of course does not show the mileage amount.