Couldn’t find any planes in the airport but there are helicopters at the helipad, both the airport and military base gates are shut but you can drive through the fence in the airport (though not much point) or fly into the military base, and the jets are there.
EDIT – easiest way to get assault rifle is kill the guy in the gatehouse at the base, then wait move away from the fence and the army guys in jeeps turn up, pretty tricky because they try quite hard to kill you. I died and still had it but once you’re out of ammo it’s gone, and I couldn’t buy any ammo for it at Ammunation. But it was good fun when you get people trying to kill you for no reason.