Incident Summary
A multi-engine helicopter experienced a catastrophic failure while cruising at 500 feet above Gulf waters. The left engine sustained a massive, uncontained, explosive failure. Shrapnel from the left engine penetrated the right engine, causing it to fail. Additional shrapnel struck the aircraft's AC and DC junction boxes, resulting in a complete electrical failure that prevented a mayday call. The tail rotor drive shaft was severed, and the fuel system was penetrated, leading to a fire in the transmission area and smoke filling the cockpit.
Sequence of Events
Unable to communicate via radio, the flight crew relied on the co-pilot's side window to visually acquire the water surface. The pilot performed a successful autorotation, bringing the helicopter to the water. However, upon touchdown, the aircraft rolled over and began to sink. The emergency floatation gear, which is electrically operated, failed to deploy due to the electrical failure. Despite the inverted position, all occupants evacuated the helicopter. The pilot then returned to the sinking aircraft and deployed life rafts for the survivors.
Investigation Findings
Examination of the left engine revealed that the compressor-to-turbine coupling had failed due to fatigue. This failure allowed the turbine to overspeed, and it ultimately burst under centrifugal loads. The uncontained failure produced shrapnel that propagated throughout the aircraft, causing the cascading damage described.
Probable Cause
Failure of the left engine compressor-to-turbine coupling due to fatigue, leading to turbine overspeed and burst under centrifugal loads.