What happened
On Monday, March 10, 2003, a Bucker CASA 1 13 and E (registration F-AZUL) departed from Muret aerodrome to perform local circuit training. During the climb, while flying in a crosswind at approximately 900 feet, the pilot experienced a sudden loss of engine power. Simultaneously, the throttle lever became physically restricted, preventing it from returning to the idle position, with the engine RPM dropping below idle levels.
The pilot attempted several emergency procedures, including switching fuel tanks and operating the fuel pump, but these actions failed to restore power. Realizing the aircraft could not reach the runway, the pilot initiated an emergency landing in a nearby field. The engine eventually stopped while the aircraft was taxiing on the uncultivated ground.
The investigation
The investigation focused on the mechanical failure and the state of the engine's induction system. Upon disassembling the carburetor, investigators discovered a cloth lodged within the venturi. This cloth was obstructing the airflow and physically jamming the throttle linkage, which prevented the pilot from controlling the engine's power setting.
Further examination of the aircraft's configuration revealed that the air intake system had been modified to mitigate icing risks. Because the aircraft was prone to icing when air was drawn from the front of the engine cowling, the intake pipe had been disconnected from the forward filter and reconfigured to draw air directly from inside the cowling. This modification left the intake pipe open and unsecured, without a filter to prevent foreign object debris from entering the carburetor.
Findings
- The primary cause of the engine failure was a maintenance oversight where a cloth was left inside the air intake duct.
- The cloth was sucked into the carburetor during flight, obstructing the venturi and jamming the throttle mechanism.
- The aircraft's air intake system lacked a filter, making it vulnerable to the ingestion of foreign objects.
- The cloth had remained in the intake for several hours of flight prior to the incident.