What happened
On July 24, 2010, a Cessna 208B, registration PR-JOS, was operating a cargo flight from Belém, Brazil, to Macapá, destined to deliver 1,200kg of mail for the Brazilian Postal Service. Approximately 46 minutes into the flight, the pilot noticed the left engine chip detector light illuminate on the multi-function alarm panel. Five minutes later, an abnormal noise was heard, followed by the immediate failure of the engine.
After attempting to restart the engine without success, the pilot initiated emergency procedures and performed an emergency water landing in the Santana River, near the town of Afuá on Marajó Island. Both the pilot and the passenger escaped the aircraft without injuries, though the aircraft sustained severe damage to the fuselage belly, engine cowling, engine, and propeller.
The investigation
CENIPA's investigation focused on the mechanical failure of the PT6A-114 engine. Investigators examined the maintenance history of the starter generator, which had been recently removed and reinstalled. The investigation revealed that while manufacturer bulletins (Service Information Letter Gen-PT-024 and Service News Letter 07-16) recommended specific cleaning and inspections of the starter generator drive shaft grooves to prevent electrical arcing and subsequent bearing fatigue, there were no records confirming these tasks had been performed during the most recent maintenance cycle.
Furthermore, the investigation looked into the operator's management of maintenance oversight. The operator maintained a secondary operational base in Belém without sufficient human resources to effectively monitor maintenance activities, which were centralized in São Paulo. This lack of oversight contributed to the failure to detect non-compliance with recommended maintenance procedures.
Findings
- The engine failure was caused by the failure of the number 1 bearing.
- Electrical arcing (pitting) was found on components within the accessory gearbox, indicating a failure in the starter generator's electrical insulation.
- Maintenance procedures recommended by the manufacturer to prevent bearing fatigue via shaft inspection were not documented as completed.
- Organizational deficiencies in maintenance supervision and the lack of adequate oversight at the secondary operational base contributed to the oversight of critical maintenance tasks.