I have flown with a Decathlon (similar frame to the bv65) and didn't need an extender. We did need to pop the black plastic piece off the back for the plane ride only and needed to recline the airplane seat to uninstall. It fit through the scanner face down in recline only. The issue we had is that when ff, the seat infront comes very close to the knees of the child when the person reclines.
I flew with the Nautilus and was able to fit it though the scanner by pressing the two red tabs at the base to disconnect the back while on the conveyor. I just rested the back backwards on the belt, and snapped it upright in place after it came out of the scanner before taking it off the belt. The issue we had on the plane was terrible headslump, much worse than in our van.
For our summer trip we picked up a sale maestro. I think it will fit through a scanner with the arm rests temporarily popped off as facedown w/o them it is only 15" or so high. My dh can take ours off in a few seconds.
Our airport security has tried to get us to check seats that wouldn't fit (we eventually made them fit), rather than wand for some unknown reason.
I called in advance this time, though, to ask for the measurements of the scanner. The guy I spoke with promised that they would wand the seat if it didn't fit (I think he thought I was nuts).