What happened
The incident occurred during ground operations involving a Boeing 727 positioned at the gate. The aircraft was initially pushed back from the gate counter-clockwise through an arc of 90 degrees. This maneuver resulted in the aircraft being mispositioned relative to its intended taxi direction.
To correct this out-of-position condition, the ground crew, consisting of tug operators and safety personnel, attempted to resolve the issue by continuing the pushback through a second 90-degree counter-clockwise arc. This corrective action required pushing the aircraft upslope across the ramp surface.
During the execution of this second arc, the tug became positioned approximately 90 degrees relative to the longitudinal axis of the towbar and aircraft. Under these conditions, the combination of the downslope gradient and the idle power settings on the aircraft overwhelmed the braking capacity of the tug. Consequently, the towbar failed under a bending load. The failure allowed the Boeing 727 to roll forward uncontrolled, resulting in an impact with the tug. Throughout the incident, all three engines of the B-727 were operating at idle thrust.
The investigation
The examination focused on the mechanical integrity of the towbar and the operational dynamics of the pushback maneuver. Investigators determined that the towbar broke due to a bending load generated by the angular misalignment between the tug and the aircraft during the second arc of the pushback.