How did they film the special forces helicopter crashes?

Question

in White House Down, We see in the following youtube clip:

That when special forces went to attack the White House, the captives fire a javelin missile at the helicopter and it crashes.

The second one hits the ground when hit by a missile and crashes into the pool (it catches fire)

The third one: Manages to deploy a few troops by fast roping onto the the White House roof, but is blown up by an incoming missile and crashes into the White house itself.

After all this the troops are still inside the helicopters.

How did they film the helicopter crashes while the troops are still in them?

Answer 1

They're almost entirely CGI....

...and blue screen composites of live action.

There's comprehensive rundown and article at FXGuide together with a video from the FX house (Method FX) as to how it was done.

Method Studios took on initial previs to further refine the actions for the three crashes, in addition to combining some gimbal-filmed shots and repelling soldiers shot on bluescreen.

The helicopters were modeled in Maya and textured in MARI. "Rivets are right on the cusp of that effort," says Rankin. "If you put them into the model, they're going to give you really nice lighting characteristics. As the light angle changes on the rivets, they pick up nice highlights. But it also makes for incredibly inefficient rendering. In this case we chose to leave the rivets in the textures, and only had to do some extra work for a few shots."