Thanks flowman, now even I understand how it works...
However... I tried one that made me a tad mad whilst planning the other day:
LFMU - EBCI, upper levels (FL390)
IFPUV answer is: DCT. (7 errors) Not very helpful, is it? Does this use the route catalogue?
Thats the route I came up with usinfg our fpl system:
DCT MEN UN871 ETREK UM976 BRY UM733 KOPOR UN874 VEKIN UZ173 ARVOL
Pretty much zig zag. 560nm vs. 431 overhead - overhead. How good we pay for emmissions to save the planet....apparently no one in France flies South-North, just the other way round.
(sorry for the sarcasm, but....)