What happened
Upon touchdown of the main gear, the crew placed the thrust levers into the idle reverse position. Once the nose gear made contact with the runway, the pilot applied braking and full reverse thrust. During this process, the aircraft began to drift to the left of the runway centerline.
In an attempt to maintain control, the pilot utilized asymmetrical braking, which resulted in no change in directional control. The pilot then attempted to use a combination of asymmetrical braking and asymmetrical reverse thrust. As a final effort to prevent the aircraft from departing the runway, the captain used the tiller. Despite these actions, the aircraft exited the runway and came to rest on a grassy area located between parallel runways.
The investigation
The aircraft was equipped with lightweight clamshell thrust reversers. During the inspection of the number 2 engine, the right-hand thrust reverser was found failed in the open (forward thrust) position. Although the failure occurred, the thrust reverser lights did not indicate any abnormalities.
Metallurgical examination of the hardware revealed an overstress fracture of the lower inner hinge, along with a fatigue fracture through the flange of the upper outer hinge.