L2022-02 Amateur-built Aircraft Accident in Tikkakoski on April 17, 2022

The pilot of an amateur-built Monnett Sonerai I airplane departed on a personal flight from Jyväskylä aerodrome, Tikkakoski, on April 17, 2022. A few minutes after takeoff, the engine started running rough and soon cut out. The pilot attempted to steer the airplane to the airfield but had to force-land in wooded terrain. Reaching the airfield after the engine cut-out from the lower-than normal traffic circuit height was beyond the capabilities of the accident airplane. The airplane impacted trees and the pilot sustained fatal injuries. The airplane was damaged beyond repair.

The engine was disassembled and thoroughly examined, but investigation revealed no technical fault that could have caused the cut-out. The amount of fuel on board was sufficient, and the fuel was of the correct grade. It is possible that the engine cut out due to the accumulation of ice or condensed fuel in the carburetor or in the inlet ducting. Carburetor location and inlet ducting configuration made them prone to icing and to formation of fuel droplets, which is a typical feature of the engine type. Weather conditions and the phase of the flight were conducive to carburetor icing. The airplane had an inlet air preheat system, but its effectiveness or application during the flight were not positively determined.

Investigation found that little Finnish language information of carburetor icing is available. The effect of temperature and dew point on the risk of carburetor icing is not apparent from aeronautical weather information, but it was discussed in canceled aeronautical information publication OPS T1-18, which is currently available on a non-Traficom server only.

Current aviation regulations do not define training and experience requirements for the builders of amateur-built aircraft, and incorrect or inappropriate knowledge or skills may lead to dangerous structural solutions or incorrect component installations. Efficient and coordinated training could improve recreational stakeholders’ knowledge of safe aeronautical practises. The first inspection conducted by the authority is undertaken during the final stage of construction, when an application for a permit to fly for test is submitted. Even if the inspection reveals serious deficiencies, reinspection will not necessarily be required.

To enhance safety, the Safety Investigation Authority Finland recommends that:

- The Finnish Transport and Communications Agency Traficom ensures that information of carburetor icing (OPS T1-18 “Kaasuttimen jäätyminen” and EGAST GA5 Piston Engine Icing or equivalent information) is made available in Finnish.
- The Finnish Transport and Communications Agency Traficom and recreational pilot associations jointly ensure that up-to-date instructional material and training are available to the builders of amateur-built aircraft, and that cooperation between the builder and the surveyor during the building project is emphasized.
- The Finnish Transport and Communications Agency Traficom establishes a practise in which the surveyor should be available for the initial airworthiness review of an amateur-built aircraft. If the inspection reveals serious deficiencies, the aircraft should always be reinspected.