NTSB Identification: CHI96LA011.
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Accident occurred Friday, October 13, 1995 in CEDAR RAPIDS, IA
Probable Cause Approval Date: 11/11/1996
Aircraft: McDonnell Douglas DC-9-31, registration: N945AX
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

Shortly after an intermediate level-off at 13,000 feet, the crew heard a loud bang and felt the airplane shudder. They diverted to a nearby airport. During the landing roll, the engine's thrust reversers were deployed. The right engine thrust reverser deploy light illuminated. The left engine thrust reverser deploy light did not illuminate. Maintenance personnel found the left engine lower thrust reverser door had been struck repeatedly by the top reverser door. An investigation revealed broken and bent thrust reverser linkages. A pivot bolt, washers, castellated nut, and cotterpin associated with a driver linkage arm were missing. Two other company airplanes were found with a missing cotterpin from the pivot bolt. Examination of these assemblies revealed the bolt end did not protrude beyond the nut's outer edge. The result was that the cotterpin could not fit through the hole in the bolt. The manufacturer's parts manual and maintenance manual text indicated that one countersunk washer should have been below the bolt head and one flat washer under the nut. However, the corresponding illustration in the maintenance manual showed an additional washer (2 washers) under the nut.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

inadequate installation of a thrust reverser, driver linkage arm pivot bolt and nut, which resulted in the nut and bolt becoming disconnected. A factor relating to the accident was: the manufacturer's unclear information regarding the type and number of washers to be installed on the pivot bolt assembly.

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