If you are respawned on the side with the helicopter there should be a broken ledge.

Make sure you have a class with marathon light weight and m9 switch to your sidearm and sprint at it.

Jump and you should be climbing up the side like a ladder, when you get to the top walk the wooden ledge and walk all the way round.

There's another ledge, jump on to it and walk up and climb onto railings and that should be it.