AI Aircraft Range?

Hi All :) Iv'e been using AITM to edit my traffic files and it's worked great except there's one thing iv'e been wondering for some time. Sometimes when i enter a flight, i get a message saying: "Warning! Aircraft range limits reached for leg 1" and it's followed by a value such as: "(100nm - 2100nm)". When editing manually, I don't see a range value anywhere
Neither the .air or CFG files of the aircraft have anything about range. The help in the program and website have nothing about it either. I usually ignore it and it usually works, but i'm just too curious about this range thing. Anyone else have any ideas?
