The error was said to have occurred because _______.

Heavy workloads on air traffic controllers were yesterday blamed for a near miss incident three miles from Heathrow Airport, London, when two passenger jets flew within 200 feet of each other. A Virgin Express Boeing 737 was attempting to land as a British Airways Boeing 737 was taking off. A catastrophe was only prevented when an inspector supervising the departures controller overheard the arrivals controller and realized he had turned the Virgin jet into the path of the BA 737, Both aircraft were then instructed by the two controllers to change course and a tremendous crash was just avoided.