FTW94IA070

One of two left main wheels separated. The subsequent landing was uneventful. The tire and wheel remained intact. The axle nut was found with the locking retainer ring installed in the groove on the nut. Evidence collected by the manufacturer indicated the retainer nut spun off of the axle with the rotation of the wheel. According to the manufacturer, 'this condition could only occur if the locking capability of the retaining ring was lost due to the retaining ring not fully seated.' The manufacturer measured the thread dimensions of the inner cylinder axles and retainer nuts. Threads on both axles and retainer nuts were beyond the manufacturer's wear limits. On the incident axle, thread engagement measurement (excluding the damaged area) for the axle was at the manufacturer's wear limit. According to the manufacturer, wear did not compromise the capability of the nut and axle. Their cross section of the nut 'did not exhibit enough deformation to support migration of the nut off the axle.'

On January 19, 1994, at 0911 central standard time, a Boeing 737-2H4, N53SW, sustained minor damage during takeoff from Little Rock, Arkansas. The crew of five and 62 passengers were not injured. Visual meteorological conditions prevailed for Southwest Airlines Flight 17, scheduled Title 14 CFR Part 121 service to Dallas, Texas, Love Field.

Flight 17 made a left turn onto runway 22R when cleared for takeoff. A witness reported to the Southwest Airlines' station that he observed a left main wheel separate from the airplane. Little Rock Air Traffic Control(ATC) Tower was then notified that the number one left main wheel departed the aircraft. During the climb through about 5,000 feet MSL, the tower informed the crew. The crew reported that all cockpit indications were normal and that they would continue the flight to the destination. Upon arrival at Dallas the crew landed and taxied to the ramp without further incident.

The tire and wheel remained intact and other parts of the wheel assembly were recovered. During a visual examination at the Southwest Airlines' Operations Facility, Little Rock, Arkansas, a Federal Aviation Administration (FAA) airworthiness inspector and company officials (statements enclosed) removed the hub cap from the wheel. They reported finding the axle nut with the retainer ring installed in the groove on the nut.

The inner cylinder and wheel components were examined at the Southwest Airlines' Quality Control Center, Dallas, Texas, by a FAA airworthiness inspector and company officials. The landing gear inner cylinder out board axle showed gouges in the axle and aluminum residue on the threads.

Southwest Airlines submitted the inner cylinder and wheel assembly to the Boeing Company for examination. Evidence collected by the manufacturer indicated that the retainer nut spun off of the axle with the rotation of the wheel and hubcap. According to the manufacturer, "this condition would only occur if the locking capability of the retaining ring was lost." The manufacturer's report is an enclosure.

The manufacturer measured (see enclosed report) the thread dimensions of the inner cylinder axles and retainer nuts. Some of the threads on both axles and retainer nuts were beyond the manufacturer's wear limits. Some roll over areas were noted on the incident retainer nut threads. On the incident axle, thread engagement measurement (excluding the damaged area) for the axle was at the manufacturer's wear limit.

During a telephone interview with Boeing personnel on July 20, 1994, they stated that the "locking capability would be lost if the retaining ring was not fully seated." They further said the axle and retainer nut "threads that were beyond the wear limits did not compromise the capability of the nut and axle." Their cross sectioning of the nut "did not exhibit enough deformation to support migration of the nut off the axle."