NTSB Factual Report

On June 9, 2010, at 1820 central daylight time, a Piper PA-34-220T, N104NW, sustained substantial damage during a hard landing on runway 36 (5,500 feet by 100 feet, concrete) at the Ankeny Regional Airport (IKV), Ankeny, Iowa. The pilot and two passengers were not injured. The 14 Code of Federal Regulations Part 91 personal flight departed Detroit Lakes (DTL), Minnesota, about 1622 with IKV as the destination airport. Visual meteorological conditions prevailed and an instrument flight rules(IFR) flight plan was filed.

The pilot reported that the flight was normal until the final approach for landing. He reported that when he pulled back on the control yoke during the flare, the nose of the airplane did not pitch up. The airplane landed hard on the nose wheel and bounced several times. The pilot maintained directional control of the airplane before he stopped it on the runway. Once stopped, he taxied the airplane to the ramp. The firewall and fuselage sustained substantial damage.

A Federal Aviation Administration (FAA) airworthiness inspector examined the airplane. Maintenance personnel removed the floorboards and tunnel panels for inspection of the control cables. The inspection revealed that the stabilator control cable had fractured in two pieces. The location of the fracture was in the unobstructed space in the tail cone. The location of the fracture was not associated with a pulley, fairlead, or bulkhead, and no rubbing or chaffing was found in the area of the fracture or tail cone. The entire length of the cable was covered with dried black grease. The cable was removed and sent to the National Transportation Safety Board’s (NTSB) Materials Laboratory for examination.

The NTSB Materials Laboratory’s inspection revealed that the cable’s composition was consistent with stainless steel. The cable fractured approximately 18 inches from the turnbuckle end and approximately 65 inches from the ball portion of the single-shank ball-end terminal. The entire length of the cable was covered with grease. The individual cable wires in the area of the fracture were found partially unraveled and the exposed surfaces were covered with grease. A majority of the fractured ends of the individual wires exhibited wear damage at a slant plane relative the length of the cable that reduced the ends of the wire to a knife edge. Wear damage reduced the majority of a wire’s cross section. The ends of the remaining fractured wires exhibited elongation deformation and cup and cone fracture features typical of overstress separation. The fractured end of the wires showed micro-void coalescence dimple features typical of overstress separation with no evidence of fatigue cracking.

On January 3, 2001, the New Piper Aircraft Company issued Service Bulletin (SB) 1048, “Stainless Steel Control Cables.” It identified Piper manufactured airplanes that had stainless steel cables installed. According to the SB-1048, the accident airplane, N104NW, serial number 34-8133059, had stainless steel control cables installed during its manufacture. The bulletin stated, “Service reports have been received stating that stainless steel cables in the aircraft control system have a considerably shorter service life as compared to galvanized cables for the same application.” The service bulletin stated that it was mandatory to inspect and maintain the control system cables in accordance with the FAA Advisory Circular (AC) 41.13.

On July 11, 2001, the FAA issued Special Airworthiness Information Bulletin (SAIB) No. CE-01-30. The SAIB recommended that owners or operators of the affected aircraft perform an inspection and possible replacement of the stainless steel cables as outlined in the Piper SB-1048. The FAA recommended that the inspections be accomplished at each 100-hour or annual inspection.

FAA AC-41.13, “Acceptable Methods, Techniques and Practices – Aircraft Inspection and Repair,” stated that the inspection and repair of control cables should be accomplished at annual inspections and during 100-hours inspections. It stated that a cloth should be passed over the cable to snag on broken wires.

The aircraft maintenance logbooks indicated that the last annual maintenance inspection was conducted on March 18, 2010. The total time on the airframe at the time of the inspection was 7,240.2 hours. The airplane had flown about 17 hours since the last annual inspection. The logbook entry indicated that the control cables were checked for correct rigging and cable tensions. The logbook entry stated, “Stabilator OK.” There was no indication of any repair or replacement of the stabilator control cable.

NTSB Probable Cause

The failure of the stabilator control cable due to wear. Contributing to the accident was the inadequate maintenance inspection of the stabilator control cable.