WPR13LA035

During a photography mission, the pilot applied full engine power, and the engine speed dropped to idle. After attempting a series of troubleshooting steps, the engine did not respond, and the pilot performed a forced landing into a field. The airplane landed hard and nosed over. Postaccident examination of the engine revealed that the outer jacket of the throttle control cable had fragmented at the carburetor attach point, exposing the inner cable. Subsequent throttle control movement resulted in the cable flexing out of the jacket, rather than moving the throttle control arm at the carburetor. No life limit existed for the cable, which was most likely installed at the time of airframe manufacture, 38 years prior to the accident. Further examination of the engine revealed no additional evidence of a mechanical malfunction or failure that would have precluded normal operation.

HISTORY OF FLIGHT On November 6, 2012, about 1100 Pacific standard time, a Cessna 172M, N21391, landed hard during a forced landing near Modesto, California. The private pilot was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91, as an aerial photography flight. The pilot and photographer/passenger sustained minor injuries; the airplane sustained substantial damage. The local flight departed Modesto City-County Airport-Harry Sham Field, Modesto, at 1042. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot and passenger departed with the intention of taking photographs of fields in the Patterson area. Having reached their destination, and after completing the first round of photographs, the passenger requested that the airplane's airspeed be reduced. While at an altitude of 1,200 feet agl, the pilot reduced the engine speed to 1,700 rpm, applied carburetor heat, 10 degrees of flaps, and reduced the airspeed to 80 knots. She then periodically increased the engine speed to confirm its operation. After about 10 minutes, the photographer requested that they climb to a higher altitude. The pilot applied forward throttle control, but the engine speed subsequently dropped to idle. After attempting a series of troubleshooting steps, the engine did not respond, and with the airplane descending, the pilot performed a forced landing into a field. The airplane landed hard and nosed over, sustaining substantial damage to the firewall, vertical stabilizer, and both wings. TESTS AND RESEARCH An inspector from the Federal Aviation Administration (FAA) examined the airplane subsequent to recovery. The nose landing gear assembly had become separated from the firewall during the accident sequence. The engine remained attached to the firewall by its mount, which sustained minimal damage. The carburetor remained attached to the inlet manifold; the inlet air filter and heat box sustained crush damage. Examination of the throttle control system revealed that the plastic outer jacket of the throttle cable had fragmented between the attach bracket and the carburetor throttle control arm. The inner armor and control cables were exposed, and movement of the cabin throttle control resulted in the cable flexing out of the jacket, rather than moving the control arm. Further examination did not reveal any anomalies with the airframe or engine that would have precluded normal operation. Refer to the engine and airframe report included in the public docket for further details. Engine maintenance records revealed that the airplane had undergone a 100-hour inspection on November 4, 2012. At that time, the airframe had accrued a total of 3,240 flight hours. There were no logbook entries indicating the throttle control cable had been replaced since the airplane's manufacture in 1974. ADDITIONAL INFORMATION A review of the FAA Service Difficulty Report database for the Cessna 172 series revealed one similarfailure of the throttle cable sheathing. This failure occurred in a 172M airplane, and the cable had accrued 3,857 flight hours. No FAA airworthiness directives or Cessna service bulletins existed for such a failure, and the cable had no life limit.