What happened
On June 18, 2010, a Pioneer 200 ultralight aircraft, registration CS-UPK, departed from Coimbra Municipal Aerodrome on a recreational flight. The aircraft was en route to the Lezíria runway in Vila Franca de Xira, flying over Figueira da Foz and Santa Cruz with one pilot and one passenger on board.
While cruising at approximately 1,800 feet near Figueira da Foz, the pilot noticed vibrations originating from the engine. Although reducing power initially mitigated the vibration, the intensity soon increased, accompanied by a drop in engine RPM and a significant loss of power. As the cylinder head temperature on the right side began to decrease, the pilot was forced into a gradual descent to maintain airspeed and lift. Unable to reach the intended airfield at Monte Real, the pilot executed a precautionary landing on a beach near Pedrão, Vieira de Leiria. The landing was successful, and the aircraft remained intact without any injuries to the occupants.
The investigation
The GPIAAF examined the Jabiru 2200 engine, which was removed and placed on a test bench. The inspection revealed signs of poor maintenance, including oxidation and deformed or fractured cooling fins. Investigators also noted that the engine's maintenance log lacked detailed records of specific actions taken during scheduled inspections.
Review of the engine history revealed that the engine had previously been involved in a different accident in 2004. Furthermore, a recent inspection in May 2010 had identified a fractured piston in cylinder number 4, which had been replaced, but the repair was not documented in the engine logbook. Additionally, cylinder number 3 had been noted as being in a worn and fragile state, with a decision regarding its replacement still pending at the time of the incident.
Upon detailed inspection of cylinder number 3, investigators found that the adjustment nut for the exhaust valve rocker arm had moved out of its normal position. This prevented the exhaust valve from opening properly, effectively causing the cylinder to cease functioning.
Findings
- The engine power loss was caused by the failure of cylinder number 3 to operate correctly.
- The failure was due to the loosening and displacement of the exhaust valve rocker arm adjustment nut, which prevented the valve from opening and blocked the discharge of exhaust gases.
- It is suspected that the nut was either insufficiently tightened or failed due to material fatigue during previous maintenance work.
- The engine was already in a degraded state, as cylinder number 3 had been previously identified as worn and awaiting replacement.
- Maintenance records were incomplete, lacking detailed documentation of recent repairs and inspections.