N3633SSchweizer Aircraft G-164B · 1986

On June 29, 2013, about 0645 central daylight time, a Schweizer Aircraft Corp. G-164B, N3633S, was substantially damaged during a landing gear collapse while landing at McKellar-Sipes Regional Airport (MKL), Jackson, Tennessee. The commercial pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local aerial application flight, which was conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 137.

At the conclusion of the aerial application flight, the pilot was returning to the departure airport. The pilot touched town on runway 2 at MKL utilizing a full-stall landing technique, and shortly thereafter, the airplane began drifting to the right. The pilot responded by applying left aileron, rudder, and brake; and as the airplane returned to the centerline, the pilot attempted to realign the airplane's direction of travel with the runway. The control inputs were ineffective, and the pilot next applied full reverse thrust and attempted to apply the brakes. The pilot noted that the application of left brake would turn the airplane further left and that the right brake was unresponsive.

The airplane continued to drift left and the right main landing gear leg collapsed. Following the accident, the pilot found that the right main landing gear wheel had broken away from its axle at the hub. Fractured portions of the wheel were later recovered from the runway.

According to Federal Aviation Administration (FAA) airworthiness records, the airplane was manufactured in March 1986. On January 6, 2012, the registered owner of the airplane submitted a request to the FAA for a replacement airworthiness certificate. According to the request letter, the aircraft logs were "burned in a hangar fire." Airframe logs covering a period between May and December 2012 were examined. An annual inspection was completed on May 20, 2012, and the maintenance log entry for the inspection stated in-part, "Wheels and brakes checked-OK." Another annual inspection was completed on December 12, 2012, and the maintenance log entry for the inspection detailed a lubrication of the landing gear wheel bearings and replacement of the brake pads. No subsequent maintenance log entries detailed any maintenance or inspection of the landing gear.

The wheel rim and bearing hub assembly were submitted to the NTSB Materials Laboratory for detailed examination. The rim was of the split design with bearing bores in the centers of each rim half and a cylindrical spacer sleeve positioned between the rim halves and concentric to the bearing bores when installed on the axle stub. The center section of each rim half, which contained the bearing bores, had broken into multiple pieces and separated from the periphery of its respective rim half. A portion of the outboard rim half's periphery was also fractured and separated into multiple pieces. Some portions of the rim were not recovered from the accident scene. Examination of the fracture surfaces on the outboard and inboard rims, along with portions of the center section pieces of each rim half identified only overstress fractures and no evidence of preexisting damage. Some fracture surfaces were smeared from contact forces and could not be evaluated. Examination of the bolts securing the two halves of the rim and their associated nuts and washers did not reveal any unusual characteristics.

The owner of the airplane reported that he had entered into a verbal contract with the operator in June 2013, and that the owner was to provide an aircraft, pilot, and aircraft insurance; while the operator would provide the fuel, agricultural application work to be performed, and CFR Part137 certificate, as well as direct the use of the airplane. The operator relayed a similar understanding of the verbal arrangement; however, the operator stated that the airplane would be operating under a CFR Part 137 certificate provided by the owner. Review of FAA records showed that the airplane owner did not hold a CFR Part 137 operating certificate. Additionally, the accident airplane was not one of the aircraft listed on the operator's CFR Part 137 operating specifications.

On August 26, 2008, about 1315 central daylight time, a Schweizer Aircraft Corporation G-164B, N3633S, registered to Howard Flying Service, operated by Howard Flying Service, Inc., experienced separation of the left main landing gear axle and wheel assembly while taxiing after landing at Fletcher Field Airport (CKM), Clarksdale, Mississippi. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 Code of Federal Regulations (CFR) Part 137 aerial application flight from CKM. The airplane was substantially damaged and the certificated commercial pilot was not injured. The flight originated about 1243, from CKM.

The pilot stated that while taxiing after landing, he applied the left brake and heard a "loud pop from the left gear." Further application of the left brake was required to keep the aircraft going straight and when he applied the left brake for the third time, the left axle and wheel assembly separated. The airplane then veered to the left and nosed up momentarily before the tail wheel contacted the ground. Damage to the lower left wing spar was noted.

Examination of the airplane by a Federal Aviation Administration (FAA) airworthiness inspector revealed that two MS20008H22 bolts and one AN509-616-35 screw that secures the axle to the left spring leg gear were fractured. The bolts and screw were retained for further examination by the National Transportation Safety Board (Safety Board's) Materials Laboratory.

Examination of the fractured bolts and screw by the Safety Board's Materials Laboratory revealed the fracture surface of the screw was damaged which precluded determination of failure mode; however, the threads were deformed. Examination of both bolts revealed ratchet marks consistent with multiple fatigue crack initiation sites.

The airplane was manufactured in 1987, and at the time of the accident had accrued 10,282.0 hours. The last annual inspection was performed on March 4, 2008, at airplane total time 9,945.0 hours. The mechanic who performed the last annual inspection stated that he used his own checklist and did not torque check the axle attachment bolts as specified in the manufacturer's Annual/100 Hour Airframe Inspection Check List.