What happened
During nighttime operations, Boeing 747 N93106 was being taxied in preparation for departure when its left wing struck the right wing of a Boeing 767. The Boeing 767 was being towed in the same direction on an adjacent parallel taxiway. Both flight crews had previously obtained clearance from ground control to perform their respective ground movements.
The incident occurred in an area where the physical separation between the parallel taxiways was insufficient to allow for the simultaneous operation of wide-bodied aircraft. Furthermore, standing procedures for ground controllers explicitly prohibited such simultaneous operations in that specific zone. The ground control position at the time was staffed by a developmental controller who was undergoing training under the supervision of a full-performance controller.
The Boeing 767 involved in the collision was being moved from Gate 75 using the call sign 'UNITED 75 TOW'. This designation was constructed by combining the airline name, the gate number, and the word 'TOW'. While the Boeing 747 was taxiing, it received clearance to proceed. Controllers later stated that they did not confuse the call signs of the two aircraft.
The investigation
Investigators examined the physical layout of the taxiways involved in the collision site. They determined that the distance between the parallel taxiways did not provide adequate separation for wide-bodied aircraft operating simultaneously. The investigation also reviewed the operational procedures governing ground control in that specific area, confirming that existing protocols forbade such concurrent movements.
Findings
The primary contributing factors included the inadequate physical separation of the taxiways and the violation of standing procedures regarding simultaneous operations. Additionally, the staffing configuration, involving a trainee under supervision, was noted as part of the operational context during the incident.