Battlefield 3

Two new vehicles added to the End Game DLC are the Vodnik AA and the HMMWV ASRAD both of which are equipped with heat seeking rockets. They typically spawn at the base so you may want to relocate to make sure your guns are in range of advancing enemy air craft.

Two direct hits are not enough to destroy an enemy air vehicle at full health, so I recommend waiting to only engage one already damaged. This way you will increase your chances of destroying the vehicle. If you get an assist and a teammate finishes off the vehicle instead, the achievement won’t pop.

Remember, you don't have to get a kill, just destroy the vehicle. So if the enemy jumps out don't worry. You will still unlock the achievement.

If you are struggling to get a kill against an enemy air vehicle, you can actually kill the enemy dropship and also get this achievement.

I did this on Conquest playing Kiasar Railroad in the Vodnik-AA and never left the main base. The dropship will fly right over your main base so it's an easy target.

When you lock onto the dropship, it will automatically deploy flares. Once they have gone, you can get two salvos of missiles off to damage the dropship. Locking on a third time will cause it to deploy more flares. Simply fire another two salvo's of AA missiles, and achievement unlocked.

I was VERY lucky. I got this in my very first game of CTF.

It was on the map Sabalan Pipeline.

Used the HMMWV ASRAD, I took it up onto a hill next to the base so it was out the way from bikes and tanks passing by.

Locked onto a chopper and it used it's ECM Jammer, I didn't fire. Locked on again and fired both missiles, TRIPPLE KILL. Achievement unlocked :)

Stayed exactly where I was for the rest of the round taking down a few more choppers, no one attempted to come and kill me.

Finished the DEFENDER OF THE EARTH assignment straight away which is...

FLY SWATER - Destroy 5 air vehicles using AA jeeps.