What happened
On May 8, 2009, an Airbus A330-302, registration OH-LTN, was operating a scheduled commercial flight from New York to Helsinki. While traversing Canadian airspace, the aircraft encountered sudden, severe turbulence.
Earlier in the flight, the aircraft had experienced intermittent turbulence, during which the captain had frequently activated the fasten seat belt sign. Approximately one hour after takeoff, the weather stabilized, the seat belt sign was turned off, and the cabin crew began preparing for meal service. Although turbulence recurred, the seat belt sign remained unlit, and the crew did not begin service, though they did not return the service carts to their secure stowage positions.
During the sudden bout of turbulence, service carts in both the forward and aft galleys became airborne and overturned. One cart struck a flight attendant who was seated and belted in the aft galley, resulting in a hairline fracture to her arm. No other passengers or crew members were injured, and the aircraft sustained no damage.
The investigation
The investigation analyzed flight data monitoring (FDM) records, which confirmed a sudden change in vertical speed and aircraft attitude consistent with the reported event. The analysis showed that the turbulence was likely caused by short-lived clear-air turbulence related to the jet stream.
Investigators also reviewed the airline's operational manuals and interviewed the crew. The investigation focused on the discrepancy between the flight deck's use of the seat belt sign and the cabin crew's activities, as well as the lack of communication between the cockpit and the cabin regarding the changing weather conditions.
Findings
- The primary cause of the injury was the unsecured service carts which overturned due to severe turbulence.
- While moderate turbulence was predicted during the flight planning phase, this information was not communicated to the cabin crew.
- The captain had the discretion to use the seat belt sign, and while it had been used earlier, it was turned off prior to the second bout of turbulence.
- There was a lack of active communication between the flight deck and the cabin crew regarding the cabin's status and the weather.
- Inconsistencies were noted between the airline's Operations Manual (OM-A) and Cabin Safety Manual (CSM) regarding terminology and specific procedures for seat belt sign usage.