What happened
On August 21, 2021, a Mini Gazelle amphibious helicopter, registration I-C768, crashed in a cornfield near Castione Andevenno, Italy. The aircraft, a basic experimental ultralight (VDS) derived from a Robinson R22, had recently been at a maintenance facility for repairs, including the replacement of a cockpit window.
After refueling and performing pre-flight checks, the pilot departed from a landing pad in Caiolo, intending to return the aircraft to its home base in Bareggio. Shortly after takeoff, while performing a 180-degree turn at an altitude of approximately 50 meters, the engine failed. The pilot attempted an autorotation but was unable to avoid impact. The aircraft sustained heavy damage, and the pilot sustained serious injuries.
The investigation
The ANSV investigation focused on the mechanical failure of the Lycoming O-320 engine and the maintenance history of the aircraft. Investigators discovered a large oil pool at the refueling site and significant oil staining on the engine's left firewall.
Detailed examination of the engine revealed that the engine had suffered a catastrophic seizure. Specifically, a connecting rod bolt in cylinder number 3 had failed, causing the rod to separate from the crankshaft and jam the engine's rotation. The investigation also found that the oil level in the sump was below the minimum pick-up level. Furthermore, evidence suggested that the oil pressure sensor line had been disconnected during recent maintenance work. A photograph provided by the maintenance facility showed the oil pressure sensor line displaced from its connection point, and the lower spark plug of cylinder 3 was found to be loose.
Findings
- The primary cause of the accident was an engine seizure resulting from a total loss of lubrication.
- The loss of oil was triggered by the failure to reconnect the oil pressure sensor line following maintenance work on the left magneto.
- This disconnection allowed engine oil to be expelled from the system during engine start, leading to insufficient oil levels for sustained flight.
- The pilot failed to perform sufficiently thorough inspections during the pre-flight and engine start phases, notably overlooking the oil pressure indications and the failure of the MR chip warning light test.
- The maintenance work, which included magneto adjustment, was likely left incomplete, leaving the aircraft in an unsafe condition.