On the train mission you go in to the past on a different train via timeportal. Before you go in grab the ammo on both sides of the door and select the heatseeker. Press X if the door doesn't automatically opens. You are given a bar at the top of the screen ignore this as long as you blow the hellicopter swiftly. Ignore the guards coming after you since the past you is shooting them. Look up there's a hellicopter. part of it (one wing) is in a red circle, fire at it rapadly.The circle shall change to the opposite side fire rapidly.The circle has now changed to the middle, you guessed it fire rapidly, the helicopter will fly off and explode.Walk through the door and return to the rest of the mission.

Oh yeah and when you get to a classy room don't bother playing the slot machine unless you want to waste some time but you wont win anything even for a 3 in a row like i did.