So obviously, the best map to do this on is Harvest, due to there being multiple Warthogs and plenty of jumps. Now the first thing you’re going to think is probably jump on the turret of a Warthog and hope you run across someone with no shields.
Let’s face it, the turret on the Warthog in Halo 4 is weak. It’s likely you’ll probably never get a kill with it while in the air, unless you’re somehow lucky to run across someone who is a one shot.
I just thought of this over night, as I was so close to getting an airborne kill, but the bullets couldn’t do enough damage to actually kill them before landing. I believe the best way to get this achievement? Get in the passenger seat. Seriously, all you need is a power weapon that can kill in a single shot and this achievement can be done no sweat. Rocket Launchers and Railguns spawn in Harvest, all you have to do is get to them, but most of the time they seem to be neglected so you probably won’t have to fight your way to it.
I was in a full Warthog and I was on the turret, the guy in the passenger seat had a Railgun and got more kills then I could on the turret! I bet he even got the achievement at one point.
Overall rule? Don’t use the turret, find a power weapon and get in the passenger seat! You’ll actually be able to get kills from there!
I hope this helps, as I will be trying it out soon enough and hopefully get that achievement.