What happened
On June 6, 2019, a Cessna 207, registration TF-MAJ, was conducting a repositioning flight from Skaftafell to Reykjavik. While cruising at 6,000 feet in clear weather conditions, the engine began running roughly near the Birtingarholt farm, near Flúðlar, Iceland.
The pilot attempted to stabilize the engine by adjusting the mixture, propeller pitch, and throttle, but the situation rapidly deteriorated. Blue smoke emerged from the engine cowling, and the engine oil check hatch blew open, spraying oil across the aircraft. This oil spray coated the forward windshield, severely obstructing the pilot's forward vision and forcing reliance on the side windows.
As the aircraft descended at a rate of approximately 1,000 feet per minute, the engine lost most of its power during a turn to base. The pilot declared an emergency and executed an emergency landing in a field near the farm. The aircraft landed at an airspeed of 70–80 knots, and while the landing was successful with no injuries, the engine sustained catastrophic damage.
The investigation
An investigation by the RNSA, involving specialists from the manufacturer and the US NTSB, focused on the mechanical failure of the Continental IO-520F13B engine. The engine had been part of a factory overhaul in 2015 and had accumulated 1,290.3 hours toward its 1,900-hour overhaul interval.
A teardown inspection revealed that the failure originated in the connecting rods. Specifically, the small end bushing in connecting rod no. 4 migrated and the piston pin left its seat. This primary failure caused secondary damage to other components, including migration and damage to the small end bushings in connecting rods no. 3 and no. 6. The inspection also confirmed that the engine had undergone a 50-hour maintenance inspection just three days prior to the incident, with no issues found in the oil or filter at that time.
Findings
- The primary cause of the engine failure was the migration of the small end bushing in connecting rod no. 4, which led to the piston pin leaving its seat.
- Secondary damage occurred in other connecting rods due to the initial failure.
- The engine failure resulted in significant oil leakage, which obscured the pilot's forward visibility during the emergency descent.
Safety action
- The RNSA issued a safety recommendation to Continental to implement necessary quality assurance steps to ensure that connecting rods and small end bushings conform to required specifications and standards.