What happened
On September 12, 2014, a Japan Airlines Boeing 767-300, registration JA654J, was operating a scheduled flight from Tokyo International Airport to Gimpo International Airport. The flight was carrying 218 passengers and 11 crewmembers. During the descent, the flight crew received information from ground support suggesting that no significant convective clouds required a deviation from the approach course.
As the aircraft descended through thin clouds toward 16,000 feet near the GUKDO waypoint, it encountered sudden, intense turbulence. The aircraft experienced significant vertical acceleration, fluctuating between +1.5 G and -0.2 G. This violent shaking lasted approximately three seconds. While the passengers were not injured, the turbulence caused several cabin crewmembers and interpreters to be thrown into the air. One cabin attendant sustained a serious injury after falling onto the floor.
The investigation
The JTSB investigation focused on the meteorological conditions and the effectiveness of the aircraft's onboard detection systems. Investigators examined radar data from the Incheon Terminal Doppler Weather Radar, which revealed that while convective echoes had previously been attenuating, they began to rapidly redevelop near the accident site shortly before the encounter.
The investigation also reviewed the flight crew's use of the airborne weather radar. At the time of the encounter, the radar's antenna tilt was set to auto mode. Because the aircraft was descending at a rate of 2,800 feet per minute, the auto-tilt function adjusted the radar beam upward to reduce ground clutter, which effectively prevented the system from detecting the developing convective cells located ahead and below the aircraft's flight path.
Findings
- The primary cause of the turbulence was the encounter with redeveloping convective clouds that had grown in intensity after a period of weakening.
- The flight crew was unable to identify the approaching weather in a timely manner because the airborne weather radar antenna tilt was set to auto mode, which caused the radar beam to look over the developing cells during the descent.
- Visibility was restricted by thin clouds, making visual identification of the convective activity impossible.
- The crew relied on outdated weather information that suggested no deviation was necessary, as the convective activity had redeveloped after the last report was issued.
Safety action
Following the investigation, the airline notified its flight crews regarding the specific limitations of the airborne weather radar in auto-tilt mode. The company also instructed crews to be more proactive in manually adjusting radar tilt to scan the flight path and to implement the seatbelt sign earlier as a preventive measure during descent.