ERA22LA167

The flight instructor and student pilot completed several touch-and-go landings and on the final circuit in the traffic pattern, while on the final approach, the student pilot turned the yoke, and felt a sensation like the aileron cable disconnecting. The flight instructor took control of the airplane and noted that he could turn the control yoke 360° without a response from the airplane. Having no aileron control, the airplane veered to the right and descended into trees. A post-impact fire ensued that destroyed the airplane. Examination of the wreckage revealed that there was a break in the aileron control cable system near the right control column. A metallurgical examination of the break in the aileron control cable revealed that the mating fracture surfaces exhibited a flattened area over more than half the cable cross-section, with the remainder of the wires exhibiting features consistent with overstress fractures. The wires in the flattened area exhibited consistent, parallel streaks and witness marks. These marks may indicate wear from rubbing against an adjacent component in this area or they may be consistent with some partial cutting operation. If rubbing of the cable was creating wear, this process would have removed material wire-by-wire, and strand-by-strand over time. The remaining wires would have fractured from tensile overstress when there were no longer enough intact wires to carry the stress. It’s likely the overstress fracture occurred during the final leg of the traffic pattern, which was consistent with reports from the pilot and flight instructor that the flight controls no longer functioned properly during the final landing approach. According to maintenance records, the airplane was inspected, in accordance with the maintenance manual and Part 43 appendix D, 9 times during the 13 months before the accident. According to both inspection checklists, the aileron control cable should have been inspected and found unairworthy at some point due to its condition. Therefore, it’s likely maintenance personnel overlooked the damaged aileron control cable during the most recent inspections.

On March 25, 2022, about 1048 eastern daylight time, a Cessna 172, N62283, was destroyed when it was involved in an accident near Winder, Georgia. The flight instructor was seriously injured and the student pilot received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. According to the student pilot, they performed a preflight inspection of the airplane with no anomalies noted. They departed Gwinnett County Airport (LZU), Lawrenceville, Georgia, and flew to Barrow County Airport (WDR), Winder, Georgia, and performed several circuits in the traffic pattern. While on the final approach leg of the traffic pattern to runway 31, the student pilot turned the yoke to the right “and felt it give as if a cable had become detached.” The flight instructor took control of the airplane and experienced the same effects; the yoke could be turned in a “complete circle with no response” from the airplane. The airplane veered to the right and descended into trees. A post-impact fire ensued that consumed the fuselage and wings. The airplane came to rest about ½-mile from the approach end of runway 31 in a wooded area. Examination of the airplane revealed that flight control continuity was established from the cockpit to the elevator and rudder. A review of the aileron control system revealed that the right direct aileron control cable was attached to the control yoke turnbuckle, but was separated in the area near the the control yoke pulleys under the cockpit floor (see figure 1). No other anomalies were noted with the airplane. Figure 1. Diagram and photograph of broken aileron cable. The aileron control cable was removed from the airplane and sent to the National Transportation Safety Board Materials Laboratory for examination. Examination of the cable revealed that about 10 wires that were elongated past the fracture surface exhibited erratic deformation directions. These wires exhibited angled fracture surfaces, or localized necking near the fractures. About half of the other broken wires, particularly in the core, exhibited flat surfaces with smearing or wear lines. The direction of these smearing lines was consistent across multiple wires. Furthermore, several wires exhibited features consistent with a tensile overstress fracture (see figure 2). Figure 2. View of the fractured ends of the aileron cable, positioned in the location consistent at fracture, post-cleaning of both sides. On August 17, 2021, at an aircraft total time of 24,420 flight hours, an entry in the airframe maintenance log indicated that the right inboard flap support rib was cracked. At that time, it was noted “disconnected right aileron and flap control cables…..re-connected control cables using new hardware, and set cable tensions to manufacturers specified limits.” A review of the airframe maintenance log revealed that between February 2, 2021, at a aircraft total time of 24,054.7 hours, and the date of the accident,there were 9 entries in the maintenance logbook that stated “completed a 100 HR inspection IAW [in accordance with] MM [maintenance manual].” Furthermore, all entries stated that the “aircraft has been inspected in accordance with a 100 Hr inspection IAW FAR 43 appendix D and maintenance manual and is approved for return to service.” The aircraft total time at the time of the accident was 24,830 hours. According to Appendix D to Part 43, “Each person performing an annual or 100-hour inspection shall inspect (where applicable)…flight and engine controls for improper installation and improper operation.” According to the Cessna 172 Maintenance Manual, during each 100-hour inspection, “Aileron structure, control rods, hinges, balance weights, bellcranks, linkage, bolts, pulleys, and pulley brackets – check condition, operation and security of attachment.” Furthermore, the 200-hour inspection lists “Ailerons and cables – Check operation and security of stops. Check cables for tension, routing, fraying, corrosion, and turnbuckle safety. Check travel if cable tension requires adjustment or if stops are damaged. Check fairleads and rub strips for condition.”