Overview
On June 10, 2017, at 16:52 local time, an Aero AT-3 R100 single-engine aircraft, registration SP-ACN, was on a ferry flight from Pruszcz Gdański (EPPR) to Wrocław-Szymanów (EPWS) when the pilot observed rising cylinder head temperatures and falling oil pressure, accompanied by a coolant odor. The pilot declared an emergency and landed at Bydgoszcz-Szwederowo (EPBY) without further incident.
Incident Details
The aircraft, a two-seat low-wing monoplane with a Rotax 912S2 engine, had departed at 15:57 LMT. About 55 minutes into the flight, the pilot noticed the cylinder head temperature first enter the yellow (caution) range and then the red (critical) range. Simultaneously, oil pressure dropped and oil temperature increased, occasionally reaching the red zone. The pilot reduced engine power and initiated a descent, during which the temperatures and pressures gradually returned to normal. After landing at 17:03 LMT, a post-flight inspection revealed a crack in the plastic coolant reservoir, with coolant leakage visible on the fuselage. The crack ran from the lower right front corner upward along the front edge.
Investigation Findings
The investigation, conducted by the aircraft manufacturer under the oversight of Poland's State Commission for Aircraft Accident Investigation (PKBWL), determined that the coolant reservoir's cap vent hole was approximately 80% blocked. This blockage disrupted the cooling system's proper function, causing the coolant to boil inside the reservoir. The resulting pressure increase led to the crack and subsequent loss of coolant, which in turn caused the engine overheating symptoms. The aircraft had accumulated 122 hours and 4 minutes total flight time at the time of the incident. The pilot held a valid PPL(A) with appropriate ratings and had 470 hours of total flight experience. No pre-existing mechanical issues were found, and the reason for the vent blockage could not be determined.
Conclusion
The pilot's decision to perform a precautionary landing was deemed correct. The aircraft sustained no damage beyond the cracked coolant reservoir, which was replaced. After ground tests, the aircraft was returned to service. No safety recommendations were issued.