FTW95IA348

During takeoff at Lubbock, Texas, the number three wheel assembly separated from the axle. The aircrew continued the flight and landed uneventfully at Albuquerque, New Mexico. Company maintenance records indicated the wheel assembly was last replaced on August 16, 1995. Examination of the aircraft revealed that the axle nut was intact on the axle along with the tang washer. The axle nut locking ring was also in place. The outer bearing was found deteriorated with only its inner race remaining, and the inner bearing remained intact on the axle. Examination of the components revealed that, an incorrect inner bearing had been installed inadvertently by the wheel assembly supplier on the number three wheel assembly. A Timkin part number 594 bearing was installed in lieu of the correct Timkin part number 596 bearing.

On August 18, 1995, at 1155 central daylight time, a Boeing 737- 3H4, N309SW, sustained minor damage as the number three main wheel separated from the axle on gear retraction during takeoff from Lubbock International Airport (LBB), Lubbock, Texas. The crew of five and 109 passengers were not injured. Visual meteorological conditions prevailed for the Southwest Airlines Flight 866, scheduled Title 14 CFR Part 121 flight to Albuquerque, New Mexico.

Personnel in the Lubbock Air Traffic Control (ATC) Tower observed the number three right main wheel depart the aircraft. During the aircraft's climb, the tower informed the crew of the event. The crew reported to ATC that they would continue the flight to the destination. Upon arrival at Albuquerque (ABQ), New Mexico, the crew landed the aircraft and taxied to the ramp without further incident.

Examination of the aircraft at Albuquerque by company maintenance personnel and a Federal Aviation Administration (FAA) inspector revealed the axle nut was intact on the axle along with the tang washer. The axle nut locking ring was also in place. The outer bearing was found deteriorated with only its inner race remaining. The inner bearing was still intact on the axle. Company maintenance records indicated the wheel assembly was last replaced on August 16, 1995.

Examination of the wheel components by company maintenance personnel, a FAA inspector, and the investigator-in-charge, revealed that an incorrect inner bearing had been installed on the number three wheel assembly. A Timkin part number 594 bearing was installed in lieu of the correct Timkin part number 596 bearing.

The supplier of the wheel assembly, reported to Southwest Airlines, that in their opinion the 594 bearing was inadvertently packed with Mobil 28 grease (red) instead of Aeroshell 5 grease (yellow), and placed into customer stock without an identification tag. Since the 594 and 596 bearings are very similar in appearance once packed with grease, the 594 bearing was misidentified by a small parts area mechanic as a 596 bearing. The bearing was also retrieved from customer stock without the assistance of a certified material control inspector.

While bearing part numbers are listed on the process card that travels with the wheel halves, they were not listed on the portion of the card that travels with the small parts. In three instances, the small parts mechanic, the finished mechanic, and final inspector did not verify the number on the bearing. (See enclosed letter.)