An Atlas Air Boeing 747 and a United Airlines Boeing 737-300 involved in a runway incursion this summer at Chicago O’Hare came within 35ft (11m) of colliding, much closer than originally believed, the US National Transportation Safety Board (NTSB) has revealed. To see the animation click here

In the aftermath of the July 23 incident, US authorities estimated the aircraft came within 200-300ft of each other, although this was understood to be the distance between the fuselages as the 737 passed above the 747, and not the measurement between the widebody’s tail and the 737’s undercarriage.

Now a three dimensional animated reconstruction of the runway incursion is being displayed on the NTSB’s web site based on information from the flight data recorder, air traffic communication, recorded radar data, and aircraft performance data.

The computer simulation shows how the United 737, operating as flight 1015, was cleared for takeoff on runway 27L just as the Atlas freighter was crossing the intersection with 27L, after landing on 14R. The 737 was able to take off, but overflew the larger aircraft, clearing the tail by only 35ft.

The information confirms the two aircraft came much closer to colliding than originally thought, says a NTSB spokesman.

NTSB officials believe controller error caused the incursion. The agency cites the serious near collision as a reason why the US FAA should implement a runway collision avoidance system that will ensure the safe movement of aircraft on the ground and provide direct warning capability to flight crews.