What happened
On August 15, 2019, an All Nippon Airways Boeing 787-8, registered JA808A, was operating a scheduled flight from Tokyo International Airport to Beijing Capital International Airport. While cruising over the Inner Mongolia Autonomous Region, the flight crew identified cumulonimbus clouds and adjusted the aircraft's heading to avoid the weather.
During a descent to 3,600 meters, the aircraft was instructed by air traffic control to change its heading to avoid a flight restriction area. As the aircraft descended through cloud layers, the crew observed gathering cumulus clouds below. Although the pilot attempted to maintain level flight to avoid the developing weather, the aircraft eventually skimmed the top of a cumelus cloud at approximately 5,500 meters. At 20:23:58 JST, the aircraft encountered sudden, violent shaking, with vertical acceleration fluctuating between +2.16 G and +0.37 G.
Because the fasten seat belt sign was activated at nearly the same moment the turbulence hit, the cabin crew had no opportunity to warn passengers or secure the cabin. Two passengers sustained serious injuries: one suffered an avulsion fracture to the foot while standing near a lavatory, and another suffered a lumbar compression fracture while seated in a lavatory. Additionally, two cabin crew members sustained minor injuries after losing their balance during the disturbance.
The investigation
The Japan Transport Safety Board (JTSB) examined flight recorder data, meteorological satellite imagery, and crew statements. The investigation focused on the aircraft's flight path relative to convective activity and the timing of the crew's safety notifications. Investigators analyzed the vertical acceleration recorded by the Enhanced Airborne Flight Recorder (EAFR) and reviewed the airline's operational manuals regarding turbulence procedures and passenger announcements.
Findings
- The severe turbulence was caused by the aircraft flying in close proximity to the tops of rapidly developing cumulus clouds characterized by intense convective activity.
- The flight crew was unable to provide sufficient warning to the cabin because an ATC instruction to change heading forced the aircraft into a path that required immediate activation of the fasten seat belt sign.
- The aircraft shook violently due to strong atmospheric disturbances encountered while skimming the cloud tops.
- The lack of timely notification prevented cabin crew from securing loose items and ensuring passengers were seated, contributing to the injuries sustained.