What happened
On the evening of 19 June 1998, a Hughes 269 C helicopter, registration EI-VIP, was conducting a private familiarization flight near Loughshinny, Co. Dublin. The flight, which began at the National Show Centre in Cloghran, was intended to introduce a passenger to helicopter flight. After an initial climb to 2000 feet and a period of normal operation, the pilot experienced a sudden shudder and a leftward yaw. Within seconds, the engine RPM dropped to zero and a low voltage warning light illuminated.
In response to the sudden loss of power, the pilot initiated an autorotative descent. After rejecting landing sites containing steep inclines and high-tension cables, the pilot selected a ploughed field. While attempting the landing, the aircraft's skid undercarriage caught in cabbage and potato drills that were oriented perpendicular to the flight path. This caused the helicopter to trip and flip onto its nose, eventually coming to rest in an inverted position. Both the pilot and the passenger, who sustained minor injuries, exited the aircraft through the pilot's door. There was no post-crash fire.
The investigation
The AAIU examined the wreckage and conducted extensive mechanical testing. The investigation focused on identifying the cause of the sudden engine stoppage. Engineers inspected the air filters, fuel lines, magnetos, and engine compression. A fuel sample taken from the site was found to be clean, standard Avgas with no signs of contamination.
To further investigate, the engine was removed and placed on a test bed under supervision. The engine performed perfectly during three hours of testing, even when the magnetos were switched off individually or fuel pressure was varied. The fuel control unit was also sent to the manufacturer in the United States for specialized bench testing and strip inspection, which yielded no defects. Additionally, the investigation looked into a recently replaced electric fuel pump, but found it was correctly installed and functioning at a satisfactory flow rate.
Findings
- The engine, fuel system, and magnetos showed no mechanical or electrical defects that could account for the in-flight stoppage.
- The engine stoppage remains unexplained, as all components functioned normally during subsequent testing.
- The aircraft's skid undercarriage dug into the uneven rows of crops, causing the aircraft to tumble.
- The use of four-point harnesses by the occupants was a critical factor in preventing serious injury during the inversion.