What happened
On 26 July 2005, a Boeing 747-443, registration G-VROM, was operating a scheduled passenger flight from Nassau, Bahamas, to London Gatwick. During the climb to a cruising altitude of FL310, the flight crew monitored weather radar, which showed convective activity well away from the intended flight path. Because the flight conditions appeared smooth, the seat belt signs were turned off, allowing passengers and cabin crew to move about the cabin.
While cruising approximately 100 nm northeast of Nassau, the aircraft encountered an area of unexpected severe turbulence. The onset of the disturbance was initially light, but the intensity increased rapidly. During the peak of the encounter, the aircraft experienced vertical accelerations as high as +2.13g. The suddenness of the turbulence prevented cabin crew and a third crew member from returning to their seats, and some passengers were unable to secure their seatbelts in time. As a result, 14 crew members and 10 passengers sustained minor injuries.
The investigation
The investigation examined the flight planning, weather data, and aircraft performance during the encounter. Data recovered from the Flight Data Recorder (FDR) and ACARS confirmed that the aircraft entered a period of significant vertical acceleration. The investigation also reviewed the flight planning process, noting that the route had been designed to pass south of Tropical Storm Franklin. The flight planning officer had selected this route to avoid the storm's center, and while the crew had reviewed SIGMETs for the area, they had not been alerted to turbulence in the specific area (K23) that the aircraft subsequently entered.
Following the event, the flight crew consulted with company operations and maintenance control. The aircraft was found to be fully serviceable, and the flight continued to its destination without further incident.