What happened
On 16 August 2004, a Boeing 777-236, registration G-VIIO, was operating a scheduled passenger flight from Orlando Airport to London Gatwick. Following a departure delay, the aircraft began its climb toward a planned cruising altitude of FL370. During the ascent, the flight crew monitored the weather radar, which showed only light green precipitation returns located to the left of the flight path, with no significant weather directly ahead.
As the aircraft approached FL3 20 while climbing through IMC, it suddenly encountered severe turbulence. The encounter caused the indicated airspeed to drop by roughly 20 knots and triggered a momentary activation of the stick shaker. During this period of instability, one passenger sustained a broken ankle and five crew members suffered minor injuries. The crew subsequently reactivated the seat belt signs.
Following the event, the crew notified Jacksonville area control and monitored the situation regarding other aircraft. After consulting with the Cabin Service Director and seeking medical advice regarding the injured, the decision was made to proceed to London Gatwick. The commander declared a medical emergency, and the aircraft was provided with an expedited arrival route.
The investigation
The investigation examined the weather radar settings and the crew's decision-making regarding passenger comfort. The crew had decided to switch off the seat belt signs because the aircraft had been in smooth air for approximately ten minutes and passengers had been seated for nearly two hours. The investigation also reviewed the radar returns, noting that the display showed only light precipitation returns (green) and no higher-intensity echoes that would typically indicate more significant weather.
Findings
- The severe turbulence occurred while the aircraft was flying through areas of light precipitation indicated by green radar returns.
- The weather radar intensity does not serve as a direct indicator of turbulence strength.
- The passenger injury occurred while the individual was standing near the lavatory facilities.
- The crew's decision to switch off the seat belt signs while flying through green radar returns was a contributing factor to the injuries sustained.
- Following the incident, the operator instructed the commander not to deactivate seat belt signs while the aircraft is traversing areas showing green returns on the radar.