What happened
On 17 December 2009, a Blue1 flight, BLF284, operating an AVRO 146-RJ85, registration OH-SAK, experienced a significant fuel supply issue during a scheduled flight from Vaasa to Helsinki-Vantaa. The aircraft was carrying 64 passengers and four crew members.
Approximately 11 minutes after takeoff, during the climb, the flight crew received a warning indicating a low fuel level in the right inner engine feed tank. While the crew began following the associated emergency checklist, they continued the flight toward Helsinki rather than diverting. As the aircraft passed Tampere, the fuel level in the right outer engine feed tank also began to drop. Shortly thereafter, a low-level warning appeared for the left inner engine feed tank, resulting in a simultaneous fuel supply issue across three different tanks.
During the approach to Helsinki-Vlaanta, the crew utilized a 33-degree flap setting, whereas the emergency checklist for this specific malfunction prescribed a 24-degree setting to ensure a shallower approach angle. Although air traffic control alerted rescue units to standby, the aircraft landed safely without injuries or damage to the aircraft.
The investigation
OTKES examined the technical state of the aircraft and the crew's response to the warnings. A technical inspection following the landing revealed that frozen water in the fuel had likely obstructed the transfer of fuel from the main tanks to the engine feed tanks. This blockage prevented the electric pumps from maintaining the necessary fuel levels in the feed tanks.
The investigation also reviewed the crew's adherence to the emergency procedures. It was noted that the crew did not follow the specific instruction in the checklist to land as soon as possible. Tampere-Pirkkala airport had been a suitable diversion alternative given the location, weather, and runway conditions.
Findings
- The primary cause of the fuel feed malfunction was the freezing of water within the fuel system, which restricted fuel flow from the main tanks to the engine feed tanks.
- The flight crew failed to comply with the emergency checklist instruction to land as soon as possible.
- The crew's decision-making and airmanship were insufficient, as they continued toward the destination despite the developing situation.
- The emergency checklist for the 'Feed Tank Low Level' event was found to be complex, verbose, and difficult to use effectively during an emergency.