Sniper Clash 3D: secret weapon & buttons


Question on Sniper Clash 3D:
There’s the hall room where the flag of the red team stands. When you enter the room you can follow corridors on the right side and on the left side. Most of the time there’s a grid which makes it impossible to enter the corridor on the LEFT side. But a while ago, when I played the game, the grid was absent so that i could walk into the short corridor. There was a button on the left wall, which i pushed. Then I walked to the end of the corridor. There was another grid, which moved away when i stood very close to it, so that i could pick up a grenade launcher. The weapon was only available there because I had pushed the button before.

Since most of the time the left corridor is blocked by the grid I ask myself: What was different in this one round when the grid was absent? What do I have to do to make the grid disappear, so that I can enter the left corridor? Do I have to press any other buttons? I also recognized two other buttons in the map, which can be pressed. But I have no idea what happens when I press them.
One button is in a small hideout where you can also find a med pack. The other button can be found in the wall, after you took the elevator that brings you upstairs. It shows a helicopter. Well, there’s a helicopter standing around in the map (near the flag of the blue team), but it can’t be reached, and it doesn’t seem to have any function.


Ok, I found out how it works:
First go to the hideout with the med pack and press the button that can be found there on the wall.
Then you have some time to run to the big hall and enter the left corridor (the grid will return after a while).
Press the button on the left side (wall) and run to the grid in the end of the corridor. Behind it you find the grenade launcher / RPG.

I still haven’t found out what happens when you press the button the helicopter symbol. Any ideas?