What happened
On May 17, 2020, a Jabiru SK aircraft departed from Alqueidão UL - Azambuja aerodrome for a recreational flight over the northern Alentejo coastline. The flight, carrying a pilot and one passenger, was proceeding as planned with a climb from 1,500 to 3,500 feet.
At approximately 3,000 feet, about two miles west of Fajarda, the pilot experienced intense engine vibrations and a partial loss of power, followed by the sudden stoppage of the propeller. After declaring a MAYDAY and attempting several engine restarts, the pilot performed three left-hand turns to align with the wind and executed an emergency landing in an agricultural field. Upon touchdown, the nose gear sank into the soft ground, causing the aircraft to nose over and come to rest in an inverted position. Both the pilot and the passenger were uninjured, though the aircraft sustained substantial damage to the nose gear, vertical stabilizer, rudder, left wing, and propeller.
The investigation
The GPIAAF investigation focused on the mechanical failure of the powerplant and the maintenance history of the aircraft. The investigation team examined the engine, which was a first-generation Jabiru 2200A, and analyzed the physical evidence of the component failure. The team also reviewed the aircraft's maintenance records, noting inconsistencies in the documentation of engine work.
Findings
- The engine failure was caused by the breakage of the cylinder #1 exhaust valve head from its stem.
- The fracture on the valve stem showed clear evidence of fatigue crack growth.
- The exhaust valve guide exhibited significant wear, with a gap of over 1 mm, which far exceeded the manufacturer's limit of 0.05 to 0.08 mm.
- The failure of the valve led to the destruction of the piston, connecting rod, cylinder, and the engine case.
- While the pilot was properly licensed and medically fit, the engine maintenance records showed significant gaps in time, with some periods exceeding three years without entries.
- The investigation noted that the engine was a first-generation model that required regular valve adjustments due to the use of solid lifters.
Safety action
While no formal safety recommendations were issued, the GPIAAF highlighted several lessons for the aeronautical community:
- Pilots and owners should exercise extreme care when selecting and contracting maintenance services, particularly in the non-certified, self-declared ultralight environment, to ensure quality and professionalism.
- There is a need for the development of non-commercial technical advisory networks for owners of non-type certificate aircraft.
- Commercial service providers must be aware of the safety implications of their maintenance decisions and advice.