What happened
On July 9, 2023, a H 36 Dimona touring motor glider, registration SE-TUI, was performing a flight sequence between Mellansel and Sollefteå airports. After an initial leg, the pilot intended to return to Mellansel. During the return flight, the engine lost power, causing the aircraft to descend.
The pilot identified a field near Degersjön for an emergency landing. While on short final, the pilot encountered a power line crossing the start of the field and retracted the air brakes to clear the obstacle. However, the available landing distance of 130 meters was insufficient for the required 378 meters specified in the flight manual. Consequently, the aircraft struck a grove of trees at the end of the field. The pilot escaped without injury, but the aircraft sustained extensive damage, including a broken fuselage and severed wings.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the wreckage, analyzed GNSS navigation data, and interviewed the pilot and aircraft owner. The investigation focused on the fuel system and the circumstances leading to the engine failure. Technical examinations of the fuel tank revealed it was empty upon impact, with no evidence of leaks or mechanical malfunctions in the fuel delivery system.
Investigators also reviewed the aircraft's maintenance status and found that its Airworthiness Review Certificate (ARC) had expired. Furthermore, the investigation looked into the readability of the fuel gauge and the pilot's methods for verifying fuel quantities prior to departure.
Findings
- The engine failure was caused by insufficient fuel remaining in the tank.
- The pilot miscalculated the fuel level because the fuel gauge needle does not move linearly; a reading at the midpoint actually represents only 25 percent capacity (approximately 20 liters).
- The pilot was unaware of this non-linear characteristic of the gauge.
- The numerical markings on the fuel gauge glass were difficult to read.
- No secondary method, such as a manual dipstick check or fuel weight calculation, was used to verify the fuel quantity before takeoff.
- The aircraft's maintenance and airworthiness inspections were overdue.