Hey, i know what your going through.
i played it atleast 10 times before i passed it, then forgot to save and had to pass it again but i did it straight away.
dont even bother shooting at the cars following you or the people, focus on the rocket launchers only, right next to the rocket laucher guys are barrels of explosives that u shoot to blow them up, so basicly shoot anywhere near them for a few seconds and they will blow up, theres 3 or 4 of them but u must kill them to be able to shoot the plane when its taking off on the runway.
give it a few more tries, once u remember where the rocket launchers are then its easy.
also when the plane is going down the runway dont shoot the cars following u because u wont have enough time to blow up the plane before it takes off!
i hope this helps you out a little.
let me know how you go with this
works for me