It has to be somewhere. Maybe some vehicle is disabled but not completely destroyed?

Another possibility: Although I have tested that part and all worked fine, but maybe, by some chance, the vehicle could be stuck somewhere? Try searching on the top of the hill, where the outpost is, and maybe along the road to the airport. Also, a vehicle could have passed the base and went next to the runway, near the hangars.

Also, maybe it's just bad luck - you know arma AI, it tends to get stuck in weird places. Maybe if none of the above works, you can try to restart the mission. Anyway, that part is somewhere near the beginning, shouldn't be too much work to replay. If that happens again, let me know. Although, nobody else complained, so I guess that must be just a random mishap.

Thank you for your answers! I will try again.

I tried a second time, beginning from the autosave point where you talk to your boss at the airport. Still I see only destroyed vehicles but the objective is not achieved.

So now it worked. There is one AMV-7 that comes from Marina Bay, but only when you get close to the entrance of the airport where the fixed machine gun and grenade machine gun are located.

OK then.