Korean Air flight KE2711, a Boeing 747-400, encountered turbulence at FL220. The aircraft left the cruising altitude for descent in visual meteorological conditions (VMC). Light turbulence continued. As the onboard weather radar (in auto calibrated mode with the range setting at 80 nm and the tilt angle at -1ø) showed no echo on the display, the fasten seat-belt sign was turned off. Several minutes later, the aircraft encountered a sudden violent shaking for two to three seconds. A passenger standing in the aisle to go to the lavatory was thrown off-balance, bumped into the L4 door on the back, and fell on the floor. The only significant vertical acceleration changes (an increase to +1.54G followed by a decrease to +0.34G in two seconds) recorded in the DFDR took place around 20:30. The passenger suffered broken bones. PROBABLE CAUSES It is highly probable that this accident occurred because the aircraft was shaken as it encountered turbulence during a descent, causing one passenger who was not in his seat to be thrown off-balance to sustain serious injuries. It is probable that the turbulence was caused by VWS or unstable atmospheric conditions where convective clouds developed.