What happened
On October 5, 2008, an EMB 711C, registration PT-NNF, operated by Top Line Táxi Aéreo Ltda., was performing a commercial passenger flight from Bom Jesus do Gurguéia to Teresina, Brazil. Approximately forty minutes into the flight, the aircraft began experiencing severe vibrations. The pilot elected to perform a precautionary landing at the Colônia do Gurguéia aerodrome.
Upon landing, the pilot conducted several engine and propeller tests, including fuel draining and checking propeller rotation. Because the vibration was not present while the aircraft was on the ground, the pilot decided to take off again to continue the mission. During the subsequent takeoff roll, the aircraft suffered a loss of power. The pilot was forced to perform an emergency landing in a nearby area of low vegetation. The aircraft sustained severe damage, including damage to the fuselage, wingtips, and propeller blades.
The investigation
CENIPA investigators examined the propeller assembly and discovered that the blades were set at an angle significantly beyond the permitted limit, resembling a "feathered" position. The investigation revealed that the minimum pitch adjustment screw had been incorrectly adjusted. This over-tightening of the screw had reduced the limit of the stop, allowing the pitch to drop below the minimum threshold, which increased drag and decreased thrust.
Investigators also found evidence of an oil leak in the propeller hub, which may have been present prior to the accident. The investigation explored the possibility that the operator had attempted to adjust the propeller personally to mitigate the vibrations, as the company lacked specialized maintenance personnel to oversee such critical tasks. There were indications that the vibration experienced during the initial flight phase might have been an intermittent fault that led to the unauthorized adjustment.
Findings
- The pilot's decision to depart immediately after a precautionary landing without a technical evaluation of the aircraft's condition.
- Incorrect adjustment of the propeller minimum pitch screw, which led to increased drag and loss of engine performance.
- The pilot's excessive confidence, which led to a premature decision-making process regarding the safety of the second takeoff.
- Organizational deficiencies within the operator, specifically the lack of qualified maintenance supervision and the practice of allowing unauthorized personnel to perform maintenance tasks.