For this achievement, load up the mission Tip Of The Spear, Rally Point Bravo on Heroic. You might consider it on Normal with Mythic skull (double enemy health) on as well, to prevent Jorge from downing the Banshees too quickly. Board the Falcon and take out the targets of opportunity along the way. You'll crash land shortly after encountering the EM shield. Work your way up the hill to the point where you can get to the Spire.
There will be a couple of Banshees flying overhead. Use an overcharged Plasma Pistol to stun one of them and bring it down. Run to its location. You might need to hit it once or twice more to keep it down till you can get to it.
Once you are near the Banshee, wait for it to come out of the stun (very important) then hold X to hijack it.
I found this way of doing it easier than trying to jetpack into one while it's still up in the air and it's a bit more in-character than the other solution, IMO.