Accident
On Saturday, 25 August 2012 at approximately 1740 local time, a Piper PA-18-150 Super Cub, registration LN-LJD, was involved in an accident at a private airstrip on Sørum farm in Lier, Buskerud, Norway. The pilot, a 27-year-old male with a Commercial Pilot Licence (CPL(A)), was conducting a private flight. Earlier that day, he had taken off from the farm, towed an advertising banner over the Drammensfjord and Oslofjord areas, and returned to release the banner over the farm.
Approaching to land on runway 06, the pilot had the mixture set to rich, carburetor heat on, and one notch of flaps. Dissatisfied with the approach, he decided to abort the landing and applied power. At that moment, the aircraft was approximately 50 feet above ground level at an indicated airspeed of 55 mph. The expected increase in engine power did not occur. The pilot then carried out a forced landing in a field to the right of the runway. The landing was hard; the right wing struck the soft ground, causing the aircraft to pivot onto the left wingtip and nose over onto the propeller. The pilot exited the aircraft unharmed.
The airstrip consisted of a 260-meter long grass runway. Due to a barn at the end of the runway, landings were only permitted on runway 06 and takeoffs on runway 24.
Investigation
The Accident Investigation Board Norway (AIBN) examined the engine to determine why it failed to deliver the expected power. The examination revealed:
- All four cylinders had similar compression when checked by hand-turning the propeller.
- The lower spark plugs in each cylinder were clean, indicating normal combustion.
- The air intake was intact, and the air filter was not clogged.
- No visible leaks were found in the intake pipes between the carburetor and cylinders.
- The gascolator contained clean fuel with no contamination.
- Filters in the gascolator and carburetor were clean.
- The exhaust system outlet was not blocked.
- All control linkages for throttle, mixture, and carburetor heat functioned as expected.
- One propeller blade was bent forward.
The aircraft was later rebuilt, but no findings were reported that could explain the engine power loss.
The AIBN assessed that the temperature-dewpoint spread of 6°C made carburetor icing unlikely. The spark plugs showed no soot fouling that could cause power loss. The forward bend in one propeller blade indicated that the engine was producing some power when it struck the ground. No probable cause for the engine power loss was determined.