While holding down the debug controls key (ctrl by default), WASD changes from controlling your rudder and engine power to controlling your pitch and roll. This enables you to make quick turns without dragging your mouse across the entire desk. In addition to this, using the debug controls frees up your mouse for free look. This makes its significantly easier to move your plane around so you can pan and fly at the same time (to find targets). Once you find a target and get him in your sights, let go of ctrl and use mouse for fine tuning. To summarize, while holding ctrl and using WASD to steer, you hold down shift to pan your camera around to find a target. Once the target is spotted, you align your plane for a bombing run. Once you get aligned with the target, let go of ctrl and use the mouse for the approach.