Instructions
Enter a helicopter by pressing "E." If you want to practice helicopter flight, find an empty server which is running the map "Port Valdez," as this map has a helicopter at the spawn point.
Press and hold "W" to lift the helicopter off. With vertical flight enabled, move the mouse forward to lift the nose of the helicopter and move it backwards to lower the nose. Lowering the nose while holding "W" will move you forward. Lifting the nose while pressing "W" will move you backwards. Without vertical flight enabled, up and down will be switched.
Press and hold "S" to slow the helicopter.
Press "A" to turn the helicopter to the left. Press "D" to turn to the helicopter to the right. Slide the mouse to the left or right to "roll" in that direction. This moves the helicopter sideways without turning. You can use the "roll" to circle an area without losing your target.
Press "A" and slide the mouse left or press "D" and slide the mouse to the right to turn quickly in one direction.
Tap "W" while in the air rather than holding "W" to control your speed. The trick to flying a helicopter in "Bad Company 2" is to take it slowly. You want to move forward at a decent speed, but if you are going full speed you are more likely to lose control. If you feel like you are going too fast, use "S" to slow down. Dipping the nose of the helicopter while flying at full speed is a surefire way to smash into a building.
Circle targets using the mouse roll. This is a good way to focus fire on a specific area. However, try not to stay in the area too long as soldiers will be able to lock on to you with rockets if you are not moving frequently.