Flight History
On 16 August 2004, a Boeing 777-236 (registration G-VIIO) operated a scheduled passenger flight from Orlando Airport, USA, to London Gatwick Airport. The aircraft, powered by two General Electric GE90-85B turbofan engines, departed at 2247 hours after a delay due to ATC restrictions. The flight crew comprised 15 members, with 334 passengers on board. The commander, aged 52, held an Airline Transport Pilot's Licence and had logged 16,796 total flying hours, including 3,755 hours on type.
Departure weather included light rain, broken cumulonimbus clouds at 3,000 feet, and surface wind from 140° at 5 kt. A SIGMET chart indicated the remnants of a hurricane approximately 350 nm north of Orlando.
Turbulence Encounter
During the climb toward FL370, the commander (handling pilot) set the weather radar to 5° upward and adjusted it to scan ahead. No significant turbulence was encountered initially; only green radar returns (lowest precipitation level) were displayed ahead, while amber and red returns appeared to the left of the aircraft's track. ATC directed a 10° heading change for traffic separation.
After approximately two hours of passenger confinement, the crew agreed to switch off the seat belt signs due to smooth air conditions. Shortly thereafter, as the aircraft climbed in instrument meteorological conditions (IMC) within cirrus cloud, the sky began to lighten. While emerging from cloud and approaching FL320, the aircraft encountered severe turbulence. The indicated airspeed decreased by about 20 kt, and a momentary stick shaker activation occurred. The seat belt signs were immediately selected back on. The maximum vertical accelerations recorded were +2.367g and -0.352g.
Post-Incident Actions
The turbulence resulted in one passenger suffering a broken ankle and five crew members receiving minor injuries. The commander reported the turbulence to Jacksonville area control; other aircraft in the area monitored the situation. The Cabin Service Director assessed injuries, and professional medical advice was sought regarding treatment and potential diversion. After consultation, the decision was made to continue to London Gatwick. The remainder of the flight was uneventful, and a medical emergency was declared upon arrival, allowing expedited routing.
Weather Radar and Turbulence Guidance
According to UK Civil Aviation Authority Aeronautical Information Circular (AIC) 81/2004, the significance of radar returns increases with altitude, but echo strength does not indicate turbulence intensity. In this incident, only green radar returns (indicating light to moderate precipitation) were present ahead of the aircraft, with no warning of the severe turbulence. The operator subsequently briefed the commander not to switch off the seat belt sign while flying through green returns depicted on the weather radar.