What happened
On July 16, 2014, an amphibious Cessna 206E, registration PT-DVF, was conducting a scenic flight over the Rio Negro near Novo Airão, Brazil. The flight, operated by SEAPLANE TOURS TURISMO Ltda., departed from the banks of Novo Airão heading toward the Hotel Tropical in Manaus with a pilot and one passenger on board.
While cruising at 1,500 feet, the pilot noticed fluctuations in the tachometer, indicating an increase in propeller RPM. Shortly thereafter, the propeller and its hub completely detached from the engine. The pilot immediately executed emergency procedures and successfully performed a water landing. There was no fire during the incident, and both occupants escaped the aircraft uninjured.
The investigation
CENIPA investigators were unable to recover the propeller or the hub, as the components sank into the Rio Negro. Consequently, the investigation focused on the engine, which was disassembled at an ANAC-authorized workshop. Technical examinations revealed that the engine was functioning normally until the moment the propeller detached.
Engine accessories, including the propeller governor, were tested; the governor was sent to a specialized facility in Goiânia, where bench tests confirmed it was functioning correctly and did not contribute to the detachment. Additionally, engine parameter instruments—including the tachometer, temperature indicator, and pressure indicator—were tested in another Cessuna 206 and found to be in perfect working order.
Investigators recovered the engine's crankshaft, which had snapped during flight. The crankshaft was sent to the Department of Aerospace Science and Technology (DCTA) for scanning electron microscopy. The analysis determined that the breakage was caused by material fatigue, with no evidence of corrosion found on the fracture surface. The DCTA report suggested that the fatigue was likely caused by an imbalance in the assembly that introduced loads exceeding the design specifications.
Findings
- The crankshaft failure was caused by material fatigue.
- The fatigue was likely triggered by a propeller imbalance that introduced unpredicted loads into the assembly.
- It could not be determined if or when improper maintenance occurred to cause such an imbalance, as the propeller and hub were unrecoverable.
- The aircraft sustained damage restricted to the engine and cowlings.