What happened
On January 6, 2014, a Gippsland GA-8 Airvan, registration F-ORPH, operated by Yankee Lima, was performing a cargo flight from Cayenne Félix Éboué to Maripasoula in French Guiana. During the initial takeoff, the pilot experienced irregular engine vibrations at approximately 1,500 ft while flying in a tailwind. The pilot declared an emergency, landed, and returned to the parking area after consulting with a mechanic.
Following the first incident, the pilot restarted the engine and performed ground tests, which appeared normal. However, during the second takeoff attempt, the pilot transmitted a "Mayday" call at approximately 200 ft due to a significant loss of engine power. The pilot attempted to land within the runway area but struck the ground approximately 800 meters from the threshold of runway 26. The impact resulted in one passenger being seriously injured and the total destruction of the aircraft.
The investigation
The investigation focused on the technical condition of the Lycoming IO-540-K1A5 engine and the maintenance history of the aircraft. While the aircraft's logbook showed recent periodic inspections, the pilot noted that he had experienced similar vibrations during a flight in December 2013, though this was not recorded in the logbook.
Technical analysis of the engine fluids revealed that while the fuel was clean, the engine oil contained an iron content of over 200 ppm, significantly exceeding the Lycoming alert threshold of 130 ppm. Detailed examination of the engine components revealed extensive damage to the camshaft and tappets. Specifically, most cam lobes had lost 2 to 3 mm of material, and corrosion pitting was observed on several lobes. The tappets also showed signs of spalling.
Findings
- The engine power loss was caused by abnormal wear of the camshaft lobes and tappets, which reduced the engine's maximum available power by approximately 20%.
- Corrosion pitting likely initiated the degradation of the contact surfaces.
- The high iron content in the oil confirmed significant internal metal-on-metal wear.
- The investigation noted that Lycoming engines are susceptible to such wear due to moisture condensation on the camshaft when the engine is stationary, which can lead to surface oil starvation and subsequent metal-on-metal contact. The engine in this accident was not equipped with the updated roller tappets designed to mitigate this risk.