Help in CMRT Fire & Rumble

[Westland]

I have the problem that I cannot request air strikes.I use a Forward Observer Section HQ as directed.But if I click on the airplane symbol, the airplane is crossed out with the remark "En Route". I haven't even assigned a destination to the plane yet.
No matter which side I choose (whether German or Russian) or which aircraft types, I cannot request an air strike!Weather is clear and dry.
Air attack works in all other games and modules, but not in CMRT Fire & Rumble. Is that a bug? Or do you have to do something else?