What happened
On November 29, 2013, an instructor was conducting a demonstration of an oblique takeoff in a RotorWay Exec 162 HDF, registration F-PMRA, over a rural field near Bédoin, France. During the maneuver, at an altitude of approximately four meters, a loud detonation was heard, immediately followed by a loss of engine power. The instructor performed a side-slip landing to manage the descent. During the touchdown, the left skid struck a stone, causing the helicopter to pitch forward and eventually overturn onto its left side. The aircraft sustained heavy damage.
The investigation
Investigators examined the wreckage and focused on the engine's ignition system. On cylinder number 4, only the base of the Bosch FR7DCX spark plug remained in place; the insulator and electrode had been ejected and were recovered outside the aircraft. The investigation noted that the Rotorway Exec 162 HDF is a kit-built, single-engine helicopter. Under its special airworthiness certificate (CNSK), the use of non-aviation certified components, such as these automotive-grade spark plugs, is permitted at the owner's responsibility.
Maintenance records showed that the spark plugs had been replaced in March 2013, and the aircraft had flown 44 hours and 20 minutes since that service. The instructor, a professional pilot with 1,860 total flight hours, noted that this specific model is equipped with short skids, which makes the aircraft prone to pitching forward during landings with horizontal velocity.
Findings
- The engine power loss was caused by the failure of a spark plug.
- It is suspected that a pre-existing defect or damage caused the insulator to detach and be ejected by the high-pressure gases in the combustion chamber.
- The short length of the landing skids contributed to the aircraft tipping over after hitting the stone.