Incident Overview
On May 9, 2017, at 17:40 local time, a Diamond DA20-C1 aircraft departed from EPDE airport for a training flight with an instructor pilot and a student pilot on board. The flight was conducted in accordance with training task III/5.
Sequence of Events
After passing the Kilo EPDE waypoint, a railway bridge over the Vistula River, the pilots set the engine to cruise power at 2100 RPM. Three minutes into the flight, the crew noticed uneven engine operation from the Continental IO-240 powerplant. They activated the fuel pump, which restored normal engine operation. After another three minutes, the fuel pump was switched off. Approximately one minute later, the rough running recurred, prompting the crew to again engage the fuel pump. While approaching the Whisky EPDE waypoint, the engine surged despite the fuel pump being on, resulting in a loss of about 5 knots of airspeed.
Decision and Landing
The crew decided to return to the departure airport. They set the throttle to maximum RPM, then reduced to cruise power after two minutes, maintaining that setting for the remainder of the flight. The aircraft landed without further incident.
Post-Flight Inspection
The aircraft was withdrawn from service and handed over to a maintenance organization for investigation. The following inspections were performed:
- Ignition system check: spark plugs removed, cleaned, and tested.
- Fuel system check: fuel injectors removed, washed, and blown through with compressed air.
- Cylinder leakage test performed on a hot engine: results within normal limits.
- Valve covers removed: valve springs, rocker arms, and hydraulic tappet clearances examined.
- Exhaust manifold gasket replaced.
- Engine run-up conducted: no anomalies found, engine declared airworthy.
The operator also discussed the incident with all flying and maintenance personnel.
Investigation Findings
Examination revealed excessive carbon deposits on the exhaust valve guides and stems of the engine.
Probable Cause
The probable cause of the incident was excessive carbon deposits on the exhaust valve guides and stems.
Safety Recommendations
No safety recommendations were issued by the investigation commission.