What happened
On December 10, 2013, a Beechcraft V35B, registration PT-OAT, was conducting a private passenger transport flight from Fazenda Fronteira to Juína, Mato Grosso. The flight, which included the pilot and three passengers, proceeded normally for approximately 30 minutes under visual flight conditions.
While the aircraft was on the base leg of the traffic pattern at Juína Aerodrome, the engine failed. The pilot attempted to continue the approach to runway 35, but due to insufficient altitude, an emergency landing was performed in an open field approximately 100 meters from the runway threshold. During the landing roll, the left main landing gear and the tailwheel collapsed, causing the forward fuselage and propeller to strike the ground and resulting in a break in the left wing root. The aircraft sustained substantial damage.
The investigation
CENIPA investigators examined the engine and fuel system to determine the cause of the power loss. While the aircraft's airworthiness documentation was up to date and the Avgas fuel was found to be within standard parameters, testing of the fuel pump revealed significant irregularities.
Upon bench testing, the fuel pump exhibited fluctuating parameters. Further inspection of the fuel return chamber revealed that the calibrated orifice (gicleur) was not tightened to the required torque. When the component was reinstalled with the correct torque, the pump functioned normally without oscillations. Investigators noted that there were no records of recent maintenance interventions on the fuel pump, despite the component having 650 hours since its last overhaul.
Findings
- The fuel pump's fuel return calibrated orifice was not tightened to the specified torque.
- This incorrect torque caused reduced fuel flow and pressure oscillations, leading to the engine failure in flight.
- It is hypothesized that an undocumented corrective maintenance action was performed on the fuel pump, resulting in the improper torque application.
- The pilot, the operator, and the aircraft all held valid certifications and documentation at the time of the occurrence.