What happened
While maintaining an intermediate level-off at 13,000 feet, the flight crew heard a loud bang and felt the aircraft shudder. Following this event, the crew diverted the aircraft to a nearby airport.
During the landing roll, the engine's thrust reversers were deployed. While the right engine thrust reverser deploy light illuminated as expected, the left engine thrust reverser deploy light failed to illuminate.
The investigation
Maintenance personnel inspected the left engine and discovered that the lower thrust reverser door had been repeatedly struck by the top reverser door. Further examination of the assembly revealed broken and bent thrust reverser linkages. Specifically, a pivot bolt, washers, a castellated nut, and a cotterpin associated with a driver linkage arm were found to be missing.
During the investigation, two other company aircraft were inspected, and both were found to have a missing cotterpin from the pivot bolt. An examination of these assemblies showed that the end of the bolt did not protrude beyond the outer edge of the nut, which prevented the cotterpin from being fitted through the hole in the bolt.
Discrepancies were also noted in the technical documentation. While the manufacturer's parts manual and the maintenance manual text specified one countersunk washer below the bolt head and one flat washer under the nut, the illustration provided in the maintenance manual showed an additional washer, totaling two washers, located under the nut.