What happened
On April 29, 2014, an Embraer ERJ170-100STD, registered JA211J, was operating a scheduled flight from Yamagata Airport to Tokyo International Airport. While the aircraft was descending through approximately 10,600 feet over Ishioka City, Ibaraki Prefecture, it encountered sudden and violent atmospheric disturbances.
At approximately 09:44 JST, the aircraft began experiencing fluctuations in vertical acceleration. Shortly thereafter, the aircraft experienced a significant roll to the left, reaching a bank angle of approximately 58 degrees. During this period of intense shaking, two cabin attendants working in the aft galley were thrown from their positions. One attendant sustained serious injuries, while the other suffered slight injuries.
The investigation
The Japan Transport Safety Board (JTSB) examined flight recorder data, air traffic control communications, and crew statements to reconstruct the event. The investigation focused on the aircraft's flight path, the separation from the preceding aircraft, and the meteorological conditions at the time of the encounter.
Investigators analyzed the aircraft's performance, noting that the vertical acceleration fluctuated between 0.61 G and 1.64 G for roughly ten seconds. The investigation also reviewed the separation between JA211J and the preceding heavy aircraft, confirming that the distance between the two was approximately 10 nautical miles, which exceeded the required minimum separation of 5 nautical miles.
Findings
- The primary cause of the accident was the encounter with strong wake turbulence generated by a preceding aircraft during the descent phase.
- The turbulence was particularly impactful because the stable weather conditions and calm winds allowed the wake vortices to persist longer than usual.
- While the flight crew successfully managed the aircraft's recovery by manually disengaging the autopilot and correcting the bank angle, the suddenness of the movement prevented the crew from instructing the cabin crew to fasten seatbelts before the impact.
- The aircraft itself sustained no structural damage during the event.