What happened
On November 17, 2020, a Piper PA-11, registration LV-YNN, was conducting a general aviation flight instruction mission departing from Luján aerodrome, Buenos Aires. During the flight, the crew was performing a simulated emergency maneuver at approximately 800 feet. As the maneuver concluded at 200 feet, the pilot attempted to apply power to the engine, but the engine failed to respond to the throttle input.
Following the loss of power, the instructor took control of the aircraft and selected an unprepared wheat field near Open Door for an emergency landing. Upon contact with the ground, the main landing gear became entangled in the wheat crops. This caused the aircraft to nose down, resulting in the propeller striking the ground and the aircraft subsequently capsizing. There were no fatalities or injuries to the crew, though the aircraft sustained significant damage.
The investigation
The investigation focused on the mechanical failure of the throttle system. Physical inspection of the aircraft revealed a defect in the throttle cable. Specifically, the outer sheath of the cable had ruptured because it was resting against the engine exhaust.
Investigators determined that the throttle control lacked proper fasteners or clamps. This lack of securement allowed engine vibrations to cause the sheath to rub against the exhaust manifold. Over time, this friction led to the degradation and eventual breakage of the sheath. When the pilot attempted to advance the throttle, the broken sheath caused the internal cable to displace sideways, preventing the movement from being effectively transmitted to the carburetor butterfly valve.
Findings
- The engine failed to deliver required power because the throttle movement was not reaching the carburetor.
- The throttle cable installation lacked necessary clamps, which allowed the sheath to contact the engine exhaust.
- Continuous contact with the exhaust, combined with engine vibrations, caused the structural failure of the cable sheath.
- The failure of the sheath prevented effective throttle response during the critical phase of the maneuver.