What happened
On October 3, 2003, Scandinavian Airlines flight SK946, an Airbus A330-300 with registration OY-KBN, arrived at Helsinki-Vantaa Airport, Finland, with less fuel than the required final reserve. The flight had originated from Chicago O’Hare, USA, and was scheduled to terminate at Stockholm Arlanda, Sweden, with Gothenburg as the planned alternate.
Upon entering the Stockholm terminal control area, the crew encountered low visibility procedures (LVP) in effect at Arlanda. Although the captain requested a Category II approach and managed to secure an earlier arrival slot, the reduced airport capacity led to a significantly longer approach than anticipated. The crew expected a 12-minute flight covering approximately 40 NM, but the actual approach lasted 20 minutes and covered roughly 65 NM.
During the approach, the crew realized that a missed approach would leave them with insufficient fuel to reach the planned alternate in Gothenburg. They decided to divert to Helsinki-Vantaa, which was estimated to require 400 kg less fuel. During the CAT II approach, the pilots failed to maintain visual contact with the approach or runway lights at the decision height, prompting the captain to initiate a missed approach. The crew subsequently requested clearance to Helsinki, notifying Tampere Area Control that they would land with less than the required final reserve. The aircraft landed safely in Helsinki with 1,800 kg of fuel remaining, while the required reserve was 2,300 kg.
The investigation
The investigation examined the flight planning, fuel consumption, and the airline's operational procedures. Investigators analyzed 34 operational flight plans for the same aircraft type on the Chicago-Arlanda route. The investigation established that fuel consumption during the cruise phase was higher than calculated in the Operational Flight Plan (OFP), exhausting all contingency and extra fuel before the top of descent. Furthermore, the investigation looked into the airline's RODOS planning system and how approach fuel is calculated.
Findings
- The primary cause of the incident was significantly higher fuel consumption during the flight from the missed approach at Arlanda to the landing at Helsinki-Vantaa than was calculated in the OFP.
- The crew did not account for potential delays at Arlanda caused by low visibility procedures and reduced airport capacity during flight planning.
- The aircraft had already exhausted all contingency and extra fuel during the en route phase due to higher-than-expected cruise consumption.
- The airline's fuel check procedures were found to be inadequate, as fuel checks and total consumption were not consistently recorded in the OFPs, with the last recorded check occurring well before the final stages of the flight.
Safety action
- The commission recommended that Scandinavian Airlines review its alternate airport fuel calculation basis.
- The airline was advised to instruct flight crews to account for potential approach delays caused by weather or heavy traffic when planning fuel.
- The airline was urged to ensure that flight crews perform and record fuel checks during the final stages of flight and properly document both total fuel consumed and remaining block fuel in the OFPs.