What happened
On 5 July 2010, a Finnish Commuter Airlines ATR 72-212A, registration OH-ATK, performed a scheduled flight from Kuopio to Helsinki-Vantaa. During pre-flight preparations, it was discovered that the electrical pump in the left fuel tank was inoperative. While the aircraft was permitted to fly under the Minimum Equipment List (MEL) guidelines, a mechanic advised the crew to keep the fuel crossfeed valve open at all times. The crew misinterpreted this advice, believing the crossfeed should remain active for the entire duration of the flight.
As a result of this incorrect setting, both engines were supplied exclusively from the right fuel tank. During the stop in Kuopio, the crew noted a fuel imbalance of 480 kg but did not investigate the cause or refuel the aircraft, as they believed the total fuel onboard was sufficient. On the return leg to Helsinki, the imbalance continued to grow. Approximately 17 minutes before landing, the aircraft's systems triggered a low fuel level warning for the right tank, which contained only about 160 kg of fuel. Although the crew initially reported the situation as a minor technical issue, they requested an immediate landing three minutes before arrival due to the impending fuel shortage, prompting an emergency alert at Helsinki-Vantaa. The aircraft landed with the right tank gauge reading zero.
The investigation
The investigation examined the crew's adherence to operational procedures, the technical functionality of the fuel system, and the communication between maintenance and flight crews. Investigators analyzed whether the engines would have failed had the right tank run completely dry. According to the manufacturer, ATR, the engines would not have flamed out, as the left tank would have continued to supply both engines via the jet pump.
Findings
- The primary cause was that the pilots failed to consult the MEL and the Dispatch Deviation Guide (DDG) at both the departure and arrival airports, relying instead on a misunderstood instruction from a mechanic.
- The crew failed to investigate the source of the fuel imbalance in Kuopio and did not perform refueling.
- The crew did not follow checklist instructions to land as soon as possible once the fuel shortage became a threat.
- Contributing factors included limited pilot experience, degraded performance of the captain, poor cockpit resource management, and environmental stressors such as high temperatures and a sense of urgency caused by a delayed departure.