What happened
On 14 January 2014, a Robinson R44 II helicopter, registration ZS-RSO, was conducting a private scenic flight in the Nelspruit area when the engine suddenly lost power. The incident occurred near Rocky Drift farm in Mpumalanga at an elevation of approximately 3,605 feet.
During the flight, the pilot reported experiencing moderate to severe vibrations. Within just three seconds of the initial symptoms, the engine stopped completely. The pilot observed the manifold pressure increase while the oil pressure dropped to the minimum limit. Despite the rapid onset of the failure, the pilot successfully executed an autorotation, identified a suitable landing strip on a private farm, and landed the aircraft safely. There were no injuries to the two occupants and no damage to the helicopter.
The investigation
An investigation by the SACAA AIID focused on the mechanical failure of the Lycoming IO-540-AE1A5 engine. The aircraft was moved to an approved maintenance facility where the engine was disassembled for inspection.
Investigators found that the connecting rod for cylinder number five had failed. This initial failure was severe enough to penetrate the cylinder sleeve. This event triggered a rapid chain reaction, causing the remaining connecting rods to fail due to subsequent overloads. The failure of the rod also punctured the engine casing, leading to a loss of oil and a subsequent drop in oil pressure.
Findings
- The primary cause of the engine stoppage was the failure of the connecting rod on cylinder number five.
- The failure of the initial rod initiated a sequence of overload failures across the remaining connecting rods.
- The engine experienced an oil supply failure and a drop in oil pressure as a result of the damaged engine casing.
- The pilot had very little time to react to the emergency due to the low altitude of the aircraft at the time of the engine failure.
- The investigation could not determine the exact reason for the initial connecting rod failure, though it suggested an undetermined overload during the conversion of reciprocating motion to rotational motion.