What happened
On November 14, 2009, a Cessna 150H, registration OH-CTW, was conducting a solo training flight from Tampere-Pirkkala airport. The student pilot had planned a route via Hyvinkää and Forssa, returning to Tampere-Pirkkala. While flying south of Hämeenlinna, the pilot noted deteriorating weather and decided to return to the departure airfield.
During the return, the engine RPM dropped to 2000, and increasing the throttle failed to restore power. Believing the engine had failed, the pilot notified air traffic control of an engine malfunction and difficulty maintaining altitude. At approximately 12:36, the pilot declared an emergency and announced an intention to perform a forced landing in a field. During the descent, the aircraft's right wing struck a tree at an altitude of about six meters before the plane impacted the ground, flipping onto its back. The pilot sustained serious injuries, including a broken wrist and head trauma.
The investigation
The investigation examined the aircraft's technical condition, the pilot's training records, and the meteorological conditions. Investigators found no mechanical defects in the engine itself. However, the spark plugs and exhaust pipes were heavily coated in soot, indicating a rich fuel-air mixture caused by an obstruction in the carburetor throat.
Regarding the pilot's training, the investigation revealed that the student had previously failed the "Aircraft General Knowledge" exam, which covers engine operation and carburetor icing prevention. Furthermore, the instructor's handheld radio had been left in the aircraft, preventing the supervising instructor from monitoring the pilot's communications with air traffic control. The investigation also noted that the pilot and instructor had not utilized the General Aviation Forecast (GAFOR), which had predicted freezing drizzle and icing conditions along the route.
Findings
- The immediate cause of the accident was an unsuccessful forced landing resulting from an engine malfunction.
- The engine malfunction was caused by carburetor icing.
- The pilot failed to recognize the symptoms of icing and did not activate the carburetor heat until a few minutes before the landing, which was too late to melt the ice.
- The pilot's lack of knowledge regarding engine operation and icing prevention contributed to the event.
- The decision to conduct a solo cross-country flight in weather conditions prone to icing was poorly judged given the pilot's limited experience.
- The instructor's inability to monitor the flight via radio due to the misplaced handheld radio hindered oversight.