Incident
While the aircraft was being loaded with passengers, the flight engineer noticed that the right main landing gear had partially collapsed. The gear had recently been overhauled and had accumulated 51 cycles and 126 hours of operation since its installation 21 days prior to the fracture.
Examination
A detailed examination was conducted on the aft portion of the upper and lower lugs of the trunnion. Chromium plating was found on sections of the trunnion where the overhaul manual explicitly stated that 'No Chrome' should be applied. Additionally, the spherical bearing assembly, locking bolt, and anti-rotation washer were inspected.
During normal assembly, the aft trunnion of the gear is inserted into the inner diameter of the wing-mounted spherical bearing. The spherical bearing that contacted the trunnion journal had an inner diameter measuring approximately 3.50 inches. However, the aft trunnion journal of the failed landing gear had an outer diameter measuring approximately 3.25 inches.
Maintenance procedures for landing gear replacement require that the proper sized spherical bearings—either the 3.50-inch or the 3.25-inch inner diameter—be matched with the corresponding outer cylinder aft trunnion outside diameter. In this instance, the bearing and trunnion were not of matching sizes.