History of Flight
On November 6, 2012, at approximately 1100 Pacific standard time, a Cessna 172M, registration N21391, executed a hard landing during a forced landing near Modesto, California. The private pilot was operating the airplane under 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 flight departed Modesto City-County Airport-Harry Sham Field at 1042. Visual meteorological conditions prevailed, and no flight plan had been filed.
The pilot and passenger intended to photograph fields in the Patterson area. After completing the first round of photographs, the passenger requested a reduction in airspeed. At an altitude of 1,200 feet above ground level, the pilot reduced engine speed to 1,700 rpm, applied carburetor heat, set 10 degrees of flaps, and reduced airspeed to 80 knots. She periodically increased engine speed to confirm operation.
Approximately 10 minutes later, the photographer requested a climb to higher altitude. The pilot applied forward throttle control, but engine speed dropped to idle. After troubleshooting steps, the engine did not respond. With the airplane descending, the pilot performed a forced landing into a field. The airplane landed hard and nosed over, damaging the firewall, vertical stabilizer, and both wings.
Examination
A Federal Aviation Administration (FAA) inspector examined the airplane after recovery. The nose landing gear assembly had 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. Movement of the cabin throttle control caused the cable to flex out of the jacket rather than move the control arm. Further examination found no anomalies with the airframe or engine that would have precluded normal operation.
Maintenance Records
Engine maintenance records indicated that the airplane had undergone a 100-hour inspection on November 4, 2012. At that time, the airframe had accrued 3,240 total flight hours. There were no logbook entries showing replacement of the throttle control cable 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 similar failure of the throttle cable sheathing. That failure occurred in a 172M airplane with 3,857 flight hours. No FAA airworthiness directives or Cessna service bulletins existed for such a failure, and the cable had no life limit.