What happened
On August 25, 2012, a Piper PA-18-150 Super Cub, registration LN-LJD, was performing a private flight near Sørum gård in Lier, Norway. Earlier that day, the pilot had been flying a circuit to release an advertising banner over the Drammenfjord and Oslofjord areas.
As the pilot approached the private grass airstrip for a landing on runway 06, they attempted to go around after becoming dissatisfied with the approach. At an altitude of approximately 50 feet and a speed of 55 mph, the pilot applied power, but the expected increase in engine thrust failed to materialize. This loss of engine power forced the pilot to perform an emergency landing in a field to the right of the runway. During the landing, the right wing struck the soft ground, causing the aircraft to ground loop and eventually nose over onto its propeller. The pilot escaped the wreckage without injury.
The investigation
The Norwegian Safety Investigation Authority (NSIA) conducted an examination of the Lycoming O-320 engine to identify the cause of the power loss. The investigation focused on several mechanical components, including:
- Compression levels in all four cylinders
- Condition of the lower spark plugs
- Integrity of the air intake and air filter
- Presence of contaminants in the fuel and water separator
- Functionality of the throttle, mixture, and carburetor heat linkages
- Condition of the exhaust system
Findings showed that the spark plugs were clean, indicating normal combustion, and the air intake was unobstructed. The fuel and water separator contained uncontaminated fuel, and the filters were clean. All mechanical linkages for the engine controls were found to be operating as intended. The aircraft was later rebuilt, but no mechanical cause for the power loss was identified.
Findings
- The investigation could not establish a definitive reason why the engine failed to deliver the expected power.
- Carburetor icing was considered unlikely due to the 6 ºC spread between the temperature and dew point.
- The lack of soot on the spark plugs ruled out power loss due to fouled plugs.
- Evidence from the bent propeller blade suggests that the engine was still producing some power at the moment the propeller struck the ground.