What happened
On February 27, 2002, a Cessna FA 150K, registration OH-CBX, was performing a training flight for the purpose of maintaining a pilot's rating. After completing a scheduled touch-and-go at Ranuu aerodrome, the engine stopped without warning while the aircraft was climbing at approximately 300 feet.
The pilot attempted to execute a 180-degree turn to return to the runway, but due to the low altitude and the terrain ahead—which consisted of forested areas and rocky ground—the aircraft's speed dropped to approximately 40 mph. During the turn, the pilot realized a safe return to the runway was not possible and corrected the course to avoid obstacles. The aircraft's left wing struck a snowbank at the edge of the runway, causing the plane to tilt sharply to the right and impact the ground in a 75 cm deep snowdrift. The pilot and flight instructor sustained no injuries.
The investigation
The investigation focused on the cause of the engine failure and the mechanics of the forced landing. Technical examinations of the engine, including spark plugs, magnetos, and the carburetor, revealed no internal defects or fuel impurities. While some water was found in the fuel drains, it was a negligible amount.
Specialists from the Helsinki University of Technology's aerodynamics laboratory measured the vacuum created in the fuel tanks through the vent lines. The investigation also examined the aircraft's maintenance history and the environmental conditions, noting that the aircraft had been moved from a cold hangar to a warm workshop shortly before the flight.
Findings
- The primary cause of the engine failure was the interruption of fuel supply caused by the blockage of the fuel tank vents. The blockage was created by nests built by solitary wasps.
- The aircraft was significantly overweight at the time of takeoff, exceeding the maximum takeoff mass by approximately 15 kg.
- The pilot's decision to attempt a return to the runway via a 180-degree turn at low altitude contributed to the difficulty of the maneuver, as the airspeed dropped below the optimal glide speed.
- The aircraft sustained significant damage, including a bent nose gear, a damaged propeller, and structural damage to the wings.
- It was noted that the fire extinguisher mount was improperly fitted for the specific extinguisher type on board, causing it to detach during the impact.
Safety action
- The investigation recommends that flight training programs place greater emphasis on engine failure procedures during takeoff, specifically training pilots to prioritize landing in the forward sector to avoid obstacles.
- It is recommended that aircraft owners use appropriate covers for pitot/static systems and fuel tank vents, especially when the aircraft is parked overnight, to prevent blockages from insects or other wildlife.