What happened
On March 6, 2011, an Sikorsky S-76C helicopter, registration PR-LCJ, departed from Vitória Aerodrome (SBVT) bound for the Acergy Condor helipoint. The flight was a transport operation carrying two pilots and five passengers. While cruising at 1,500 feet, the crew detected unusual noise accompanied by significant vibrations. The pilot in command immediately decided to return to the origin aerodrome to allow maintenance personnel to evaluate the situation. The aircraft landed safely without further incident, and all seven occupants escaped without injury. Subsequent inspections revealed that the flexible coupling of the engine 1 drive shaft had broken.
The investigation
CENIPA's investigation focused on the failure of the engine 1 drive shaft flexible coupling. The investigation established that the operator, Líder Aviação, had implemented a more restrictive maintenance program (PMA) than the manufacturer's recommendation. This program required the preventive replacement of the flexible coupling every 900 flight hours or 12 months.
Investigators found that during a major maintenance event on May 13, 2010, when engine 1 was replaced, the flexible coupling was incorrectly recorded as a new component. In reality, the component had already accumulated 792.7 hours of operation at that time. Consequently, the component remained in service until it reached 1,362.7 hours—more than 400 hours beyond its mandated replacement limit.
Findings
- The primary cause of the component failure was a failure in maintenance tracking, specifically the incorrect accounting of flight hours for the flexible coupling following an engine replacement.
- The flexible coupling exceeded its approved service life by approximately 462 hours.
- The crew's prompt decision to return to the airport prevented the mechanical failure from escalating into a more severe accident.
- The aircraft sustained only minor damage.