History of the Flight
On 15 April 2016, a pilot flying solo on a navigation training flight in a Guimbal Cabri G2 helicopter, registration ZK-IIH, departed Rotorua at 1532 local time. Less than 90 seconds after takeoff, the pilot heard a loud bang followed by a continuous clattering noise. He advised the tower of an engine problem and began a turn back toward the aerodrome. Shortly thereafter, smoke entered the cabin. The pilot performed an immediate landing in a paddock on a ridgeline, shut down the engine, and vacated the helicopter uninjured. The helicopter was quickly engulfed in flames and destroyed by fire.
Aircraft Information
The helicopter was a two-seat light helicopter powered by a Lycoming O-360-J2A four-cylinder piston engine. It was equipped with a dual ignition system: a conventional magneto for the lower spark plugs and a plasma electronic capacitor discharge system for the upper spark plugs. The plasma system used DENSO W24EMR-C spark plugs, which required adapters for installation on the Lycoming engine. The helicopter was manufactured in France in April 2010 and had been imported to New Zealand in June 2015.
Investigation Findings
The Transport Accident Investigation Commission (TAIC) determined that the in-flight fire was initiated by the ejection of a ceramic insulator and center electrode from one of the engine's spark plugs. The loss of the spark plug allowed the combustion flame from that cylinder to ignite the engine cooling shroud, leading to the fire. The failed spark plug was a genuine part approved by the relevant airworthiness authority, but it had not been swaged during the manufacturing process, which was required to hold the insulator in place. This type of failure was found to be extremely rare.
Safety Actions
The pilot's prompt actions, including an immediate landing and the protection provided by the engine bay firewall, prevented a more serious outcome. The Civil Aviation Authority of New Zealand issued a Continuing Airworthiness Notice regarding DENSO W24EMR-C spark plugs, and the European Aviation Safety Agency issued a Service Information Bulletin recommending inspection of such spark plugs. No formal recommendations were issued by the Commission, as these safety actions were considered sufficient.
Key Lesson
Maintenance personnel should remain vigilant for product anomalies when installing components, even those from approved suppliers.