What happened
On May 2, 2019, a T’way Air Boeing 737-800, registered HL8021, was performing a scheduled flight from Incheon International Airport to Narita International Airport. The aircraft was carrying 186 people, including the flight crew and 180 passengers.
During the descent, while at approximately 16,000 feet over Hitachiota City, Ibaraki Prefecture, the aircraft passed through a thin layer of cloud. Although the pilot had previously alerted the cabin to potential light turbulence, the aircraft encountered a sudden and intense period of shaking. Flight data recorder analysis confirmed that between 09:57:12 and 09:57:14, the aircraft experienced significant fluctuations in vertical acceleration, peaking at +2.308G, alongside changes in roll and lateral acceleration.
At the moment of the disturbance, a flight attendant was moving through the cabin to ensure passenger safety. The sudden movement caused the crew member to feel as though she were floating, leading to a severe loss of balance and a backward fall. The flight attendant sustained fractures to the right tibia and the distal end of the fibula.
The investigation
The Japan Transport Safety Board (JTSB) examined flight data recorder (FDR) records, meteorological charts, and crew statements. The investigation focused on the intensity of the aircraft's movement and the atmospheric conditions present at the time of the incident. Investigators also reviewed the pilot's prior weather assessments and the company's operational procedures regarding turbulence.
Findings
- The aircraft encountered severe atmospheric disturbance that exceeded the crew's expectations. While the onboard weather radar and pilot reports (PIREP) did not indicate turbulence at the specific site, meteorological charts showed precipitation and vertical wind shears (6 to 9 kt/1,000 ft) in the vicinity.
- The pilot had correctly identified a cloud layer and notified the cabin of potential light turbulence; however, the actual turbulence encountered was much more violent than anticipated.
- The physical impact of the sudden vertical acceleration caused the flight attendant to lose her footing, directly resulting in the leg fractures.