A report on a British Airways Boeing 777-200ER encounter with clear air turbulence last year in which a passenger was severely injured and five crew received minor injuries shows the aircraft was subjected to a maximum 0.35g negative and 2.4g positive. The aircraft had left Orlando, USA for London Gatwick on 16 August 2004, and was in the climb, emerging from cirrus cloud into clear air at 32,000ft (9,750m). Since the 334 passengers had been confined to their seats almost 2h in total, the commander switched the seat belt off, having ascertained that the only returns on the weather radar were green. Soon after the turbulence struck, a passenger who was waiting to use the lavatory suffered a broken ankle and five cabin crew received minor injuries. UK Civil Aviation Authority guidance says that the significance of any given type of weather radar return tends to increase with altitude, and that the radar echo strength does not indicate the strength of turbulence. The airline has advised its crews to leave the seat belt sign on when green returns show.

Source: Flight International