What happened
On December 20, 1994, a Beechcraft B 60, registration N-911SG, crashed near Oulunsalo, Finland, during a flight from Germany to Russia. The aircraft had landed at Oulu for refueling. During the refueling process, the aircraft was supplied with 664 liters of JET A-1 fuel, despite the aircraft requiring AVGAS 100LL.
Shortly after departing Oulu at 16:19, the pilot attempted to return to the airport, reporting engine issues. At 16:26, the pilot issued a Mayday call, stating that both engines had failed. The aircraft subsequently crashed into a forested area, striking trees and coming to rest upside down. The accident resulted in one fatality (a passenger) and two serious injuries (the pilot and a crew member).
The investigation
The investigation examined the refueling procedures, the equipment used, and the aircraft's fuel system. Investigators analyzed the fuel truck, the nozzle design, and the aircraft's fuel filler neck restrictors. They also reviewed the communication between the pilot and air traffic control, noting that the pilot requested refueling without specifying the required fuel grade. The air traffic controller subsequently informed the fuel company that the aircraft required JET A-1.
Technical examinations of the engines and fuel systems revealed that the engines had ceased operation due to the ingestion of incorrect fuel. The investigation also looked into the physical design of the refueling nozzle, which featured a Kamlock connector that was small enough to bypass the aircraft's fuel filler neck restrictors.
Findings
- The primary cause of the engine failure was the introduction of JET A-1 fuel into the AVGAS tanks.
- The aircraft's fuel filler neck was equipped with restrictors intended to prevent the use of larger JET A-1 nozzles; however, the refueling nozzle's Kamlock connector was small enough to fit through these restrictors.
- The pilot did not specify the required fuel grade to air traffic control during the refueling request.
- The air traffic controller incorrectly communicated the fuel requirement to the fuel company as JET A-1.
- The fuel tank markings on the aircraft did not include the minimum octane rating required by airworthiness standards.
- The refueling personnel accepted the fuel delivery based on a quantity provided by the aircraft's representative, who also verified the fuel sample.