What aircraft was involved and where did it happen?

The accident on 2019-03-23 involved a aircraft, registration OB-1145, at PE.

What was the probable cause of the accident?

The engine failure in flight was caused by the breakage of the crankshaft, which necessitated an emergency landing into the forest canopy.

Engine failure leads to forced landing in Peruvian jungle

A Cessna U-206G floatplane experienced an engine failure due to a broken crankshaft, resulting in a crash into the jungle canopy near the Pucate River.

What happened

On March 23, 2019, a Cessna U-206G floatplane, registration OB-1145, operated by Alas del Oriente S.A.C., was performing a flight from Iquitos to the San Roque community on the Ucayali River. While cruising at 4,500 feet near Nauta, the pilot descended to 1,500 feet to maintain visual contact with the terrain due to cloud cover.

During the flight, the engine suffered a sudden loss of power and subsequently shut down. Despite the pilot's attempts to restore power by activating the auxiliary electric fuel pump and switching fuel tanks, the engine remained non-operational. As the aircraft descended rapidly, the pilot attempted to locate a suitable river for an emergency water landing. Unable to find a clear path, the pilot performed an emergency landing into the treetops (arborization).

The impact with the trees caused the left wing to separate from the fuselage. The aircraft then entered a spin and crashed into a swampy area near the Buenos Aires community. The aircraft and its four occupants (one pilot and three passengers) landed in a swamp. The occupants survived the impact but sustained moderate injuries. They remained in the wreckage until they were located the following morning by a search and rescue crew from a private operator, who assisted in their evacuation to a clinic in Ielquitos.

The investigation

The CIAA investigation focused on the sudden engine failure and the subsequent impact. Investigators examined the Continental Motors Inc. (CMI) IO-520-F3B engine, which had been previously rebuilt by the manufacturer. The investigation analyzed the engine's maintenance history, including a recent cylinder replacement performed by the operator's maintenance organization.

Findings

The engine failure was caused by the failure of the crankshaft, specifically the fracture of the No. 4 connecting rod arm.
The fracture was the result of fatigue caused by a combination of bending and shear stresses, along with corrosion and material defects, including pits and non-metallic inclusions.
The crankshaft had only accumulated approximately 65% of its required time before overhaul.
There was a lack of technical traceability regarding the specific condition of the crankshaft (whether it was new, overhauled, or repaired) during the engine's rebuilding process by CMI.
The investigation could not rule out the use of unapproved sealants during previous maintenance tasks, a factor previously linked to similar crankshaft failures in the IO-520 series.