Accident Description
The pilot reported that during the landing flare, as back pressure was applied, the control wheel fractured and separated at the upper left corner. The nose dropped rapidly, and the airplane impacted the runway surface first, then bounced. The pilot repositioned his hand behind the broken wheel to the control column and manipulated the broken control yoke forward to maneuver the airplane back to the runway. The nose landing gear bent, and the propeller struck the runway.
Examination Findings
The airplane, manufactured in 1962, was equipped with a polymeric control wheel. Metallurgical examination of the fracture surface revealed smooth crack arrest markings and bands of slightly different colors, indicative of fatigue cracking. The fracture location indicated the fatigue crack propagated due to tensile stress from the pilot's continual forward and aft manipulation. Discoloration and crazing suggested aging effects. The fatigue cracks likely initiated from age-related crazed cracks in an area of maximum tensile stresses. Dirt and discoloration of the fracture, along with adjacent cracks and crazes, and the depth of the fatigue crack indicated the crack had existed for a relatively long time (possibly years). Although not visible from the pilot's viewpoint, the crack occurred in an area where cracking would be most likely based on the yoke geometry.
Maintenance History
The airplane underwent its last annual inspection 17.76 hours before the accident. The manufacturer issued a Service Letter in 1964 requiring a one-time inspection and proof testing of applicable control wheels, with no further inspections required after compliance. A red dot on the forward rivet butt indicated compliance. Both control wheels on the accident airplane showed evidence of red material, indicating previous compliance with the Service Letter. In 2001, the FAA issued a Special Airworthiness Information Bulletin (SAIB) recommending that during periodic inspections, special emphasis be placed on original plastic control wheels, and that an unclear crack indication should prompt a test per the manufacturer's Service Letter. However, the SAIB did not specify the location or visual indicators for likely cracks. A review of the Service Difficulty Report database revealed 18 control wheel failures in applicable airplanes, most during critical flight phases (takeoff, initial climb, spin recovery, landing flare), with five failures occurring after the SAIB issuance.