PONCA CITY, OK, USA
N1162M
Cessna 210K
During cruise flight, the pilot retarded the throttle to initiate a descent, intending to reduce manifold pressure from 24 inches to 21 inches. As the manifold pressure dropped below 21 inches, the pilot increased the throttle; however, the manifold pressure continued to decrease until the needle reached the lowest reading on the gauge. The pilot exercised the throttle through its full range, but received no response from the engine. He then executed a forced landing to a muddy field. Postaccident examination of the airplane revealed that the throttle cable had separated. The cable was examined at the NTSB Materials Laboratory and it was determined that the cable failed as result of fatigue cracking. The outer coiled spring housing, in which fatigue was observed, had a coarse texture and contained tool marks and surface fissures. The origin of the fatigue was observed at one of the fissures. There was no corrosion or deposits observed on the exterior surface of the cord. The throttle cable had been installed new 71.3 hours prior to the accident.
On October 30, 1999, at 1800 central daylight time, a Cessna 210K, N1162M, was substantially damaged during a forced landing following a loss of engine power near Ponca City, Oklahoma. The private pilot, who was the registered owner and operator of the airplane, and his three passengers were not injured. Visual meteorological conditions prevailed and no flight plan was filed for the 14 Code of Federal Regulations Part 91 personal flight. The cross-country flight originated from the Lubbock International Airport, Lubbock, Texas, at 1500 and was destined for the Smyrna Airport, Smyrna, Tennessee. According to the pilot, the airplane was in cruise flight at 7,500 feet and he was diverting around weather when he decided to land at the Ponca City Municipal Airport, Ponca City, Oklahoma. He retarded the throttle intending to reduce the manifold pressure from 24 inches to 21 inches. As the manifold pressure dropped below 21 inches the pilot increased the throttle; however, the manifold pressure continued to decrease until the needle reached the lowest reading on the gauge. The pilot exercised the throttle through its full range, but the engine did not respond. He then executed a forced landing to a muddy field. An FAA inspector examined the airplane and reported that the nose landing gear separated and the engine firewall was displaced. He found that the throttle control cable had separated. The throttle control cable (Cessna part number C299505-0101), which was installed new 71.3 hours prior to the accident, was examined by an NTSB Metallurgist at the NTSB Materials Laboratory in Washington, D.C. The cable separated at the connection point between the flexible section and the rigid rod which is encapsulated by a brass sleeve. The flexible section is comprised of a strand of seven 0.0162 inch-diameter wires surrounded by a coiled spring cord. Examination of the fracture surface on the coiled spring cord with a low power binocular microscope revealed that a portion of the fracture surface was flat and contained features indicative of progressive cracking. A 0.15 inch long section of the coiled spring cord adjacent to the fracture surface was cut and examined with a scanning electron microscope (SEM). The metallurgist observed that "50% of the fracture face on this cord contained smooth, silky features and crack arrest positions, typical of the fatigue progression." Two areas of fatigue were noted. The origins of the two fatigue zones were located at the inside diameter surface of the cord. The SEM examination revealed that the surface of the wire from which the cord was constructed had a coarse texture and contained tool marks and surface fissures. The fatigue cracking originated from one of the fissures. The wire strands were also examined with an SEM. The examination revealed that all of the wires separated as a result of "reverse bending fatigue with initiation sites on approximately diametrically opposite sides of the individual wires." Additionally, no corrosion or deposits were observed on the exterior of the cord. The manufacturer of the throttle cable, Arens Controls Inc., of Evanston, Illinois, performed a tensile strength test on an a 3-foot section of exemplar cable from their inventory. The cable was tested in a calibrated pull test scale. The cable failed at 415 pounds. According to Arens, this "exceeds the tensile strength requirement of 375 pounds" for this type control cable.
Inadequate quality control by the manufacturer of the throttle control cable, which resulted in failure of the cable due to fatigue. A factor was the lack of suitable terrain for the forced landing.
Source: NTSB Aviation Accident Database
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