Flight History
On the morning of 7 February 2017, a flight instructor and a student pilot met at Locarno airfield (LSZL) for two training flights towards a mountain rating. After an uneventful first flight, the helicopter was refueled and a pre-flight check completed. At 10:35, the crew departed in Schweizer Aircraft Corp. 269C, registration HB-XFQ, for the second flight, visiting several landing sites north of Tenero. While overflying Losone at approximately 3500 ft AMSL, the student noticed a slight oil smell. The instructor observed that the engine oil temperature gauge indicated the maximum value and the oil pressure gauge indicated the minimum. Cylinder head temperature was normal. The instructor decided on a precautionary landing at the nearby former Ascona airfield, taking control and initiating an autorotative descent. The engine ran smoothly without unusual vibrations. At 11:16, the instructor landed the helicopter with low engine power on the paved runway without incident.
Meteorological Information
The weather was dry with light wind. Visibility was 50 km. High clouds from the northwest crossed the Alps at 12000 ft and 17000 ft above airport elevation. Temperature was 7°C, dew point 0°C, and QNH 1015 hPa.
Aircraft Information
The helicopter, a Schweizer Aircraft Corp. 269C, is a single-engine, three-seat helicopter with a skid landing gear. It is powered by a Textron Lycoming HIO-360-D1A air-cooled piston engine rated at 190 hp. The aircraft was built in 1994 and had accumulated 9803:44 hours on the airframe and 805:04 hours on the engine since overhaul at the time of the incident. The last maintenance was a 50-hour inspection on 3 February 2017 at 9801:19 hours, during which the ignition magnets were replaced. The helicopter flew 2:25 hours after that inspection. The technical records were incomplete, lacking material lists in work reports and documentation of engine runs before and after maintenance.
Engine Examination
External inspection revealed no damage attributable to the incident. Examination of the engine and lubrication system showed heavy metal contamination throughout. The oil suction screen and filter contained a large amount of metal particles, and the screen also held a long thread-like piece of sealant material. Spark plugs on cylinders #1, #2, and #4 were clean; cylinder #3 spark plugs were slightly sooted. The primary oil cooler was internally blocked. Cylinder head temperature was measured only at cylinder #2 by design. The engine was disassembled by a specialist. Injection nozzles were not clogged, but the threads in cylinder heads #1 and #3 were damaged. Piston #3 showed wear in the area of the piston pin plugs, which had exceeded wear limits. The piston pin plugs prevent lateral movement of the piston pins; if worn, engine damage can occur. The engine had been stored for about seven months (March to October 2016) without preservation, contrary to the manufacturer's recommendation for engines stored over 30 days. The engine had been overhauled in 2012, later installed in HB-XYL, then removed after a hard landing in 2014, repaired, and reinstalled in HB-XFQ.
Cause
The serious incident was due to inadequate engine maintenance leading to engine damage. Contributing factors were the poor traceability of technical records and the lack of engine preservation during the storage period.