What happened
On 3 February 2000, a Beech B200C air ambulance, registration SE-KFP, was performing an acute medical transport from Kiruna to Stockholm. The flight, which included a patient, a doctor, a nurse, and two pilots, proceeded at flight level 190 through extremely cold temperatures ranging between –37 and –41 ºC.
While traversing the airspace between Sundsvall and Gävle, the crew observed oscillating fuel flow and a loss of thrust in the left engine, which subsequently stopped. Due to the critical medical status of the patient and favorable weather, the crew elected to continue the flight toward Stockholm on the remaining engine. However, as the aircraft approached Gävle, the right engine also experienced fluctuating fuel flow and a reduction in thrust. The crew declared an emergency and diverted to Gävle/Sandviken airport. Although the left engine could be restarted during the descent, it provided only limited power. The aircraft landed safely on runway 18 without damage to the airframe or injuries to the five occupants.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the aircraft's fuel system and maintenance history. The investigation revealed that the aircraft had been refueled in Umeå and parked in a heated hangar for approximately 12 hours prior to the flight. During this period, the transition from cold fuel to a warm hangar environment likely facilitated moisture condensation within the tanks.
Technical inspections of the fuel filters and nacelle tanks uncovered a small amount of water. While the fuel quality from the storage installations in Umeå and Kiruna met all required standards, the investigation noted that the mandatory drainage of the fuel system during daily inspections had not been performed prior to the flight, which deviated from company procedures.
Findings
- The primary cause of the incident was water in the fuel turning to ice or ice crystals due to the extreme outside air temperatures, which created temporary blockages or pressure drops in the engine fuel system.
- The presence of water was likely due to condensation occurring while the aircraft was parked in a heated hangar after being refueled with cold fuel.
- A failure to follow established operational routines, specifically the omission of fuel tank drainage during pre-flight inspections, contributed to the undetected presence of water in the system.