An investigation into the sudden plunge of the Serbian president's plane has shown that it was because the co-pilot spilled coffee on the instruments panel, aviation authorities said Tuesday. The co-pilot accidentally activated the emergency slat extension when trying to clean the coffee from the panel. That reportedly caused the plane to dive and the brief shutdown of one of the engines. The co-pilot has been suspended. It's now been reported that the president will use only commercial flights, because the 34-year-old government Falcon 50 has a history of inflight problems.