What happened
On November 14, 2015, a CESSNA 172-N, registration EC-HKH, was conducting a local private flight departing from Bilbao Airport. The aircraft was flying along the coastline toward the 'November' visual approach point when the engine experienced a sudden loss of power. The pilot attempted to troubleshoot the issue by adjusting the fuel selector and increasing throttle, but the engine could not maintain power above 1,500 rpm.
Unable to reach a suitable landing site due to a crowded beach, the pilot executed an emergency ditching near Punta de Astondo in the municipality of Górliz. All three occupants—the pilot and two passengers—successfully evacuated the aircraft before it sank in approximately 10 to 15 meters of water. While the pilot and one passenger were uninjured, the second passenger sustained serious injuries.
The investigation
The investigation focused on determining the cause of the engine power loss. Investigators ruled out fuel exhaustion, as the aircraft had departed with full tanks. A technical inspection of the magneto was also conducted; despite finding corrosion from the submersion, the component was found to be fully functional on a test bench.
Meteorological data from the time of the accident showed a temperature of 19°C and a relative humidity of 66%. Investigators analyzed the potential for carburetor icing, noting that such ice can form in temperatures ranging from -5°C to 30°C when humidity is present. The investigation also reviewed the pilot's actions regarding the use of the carburetor heat system during the flight.
Findings
- The most probable cause of the engine power loss was carburetor ice formation.
- A contributing factor was the pilot's failure to correctly evaluate the existing meteorological conditions, which resulted in the failure to utilize the carburetor heat system while flying in icing conditions.
- The aircraft was flying in conditions characterized by moderate icing at cruise power and severe icing at descent power.