Accident Details
On October 12, 2019, at approximately 11:19 JST, an ATR 42-500 aircraft, registration JA01JC, operated by Japan Air Commuter Co., Ltd., experienced a sudden and severe shaking while flying at an altitude of about 10,800 ft. The aircraft was on a scheduled flight (Flight 3763) from Kagoshima Airport to Tanegashima Airport. On board were 19 persons: a pilot in command (PIC), a first officer (FO), one cabin attendant, and 16 passengers. The accident occurred over a location approximately 57 km north-northwest of Tanegashima Airport.
Flight History
According to statements from the flight crew and the injured cabin attendant, as well as flight data recorder (FDR) records, the aircraft had taken off from Kagoshima at 11:06 JST. The seat belt sign was turned off after reaching about 10,000 ft, and the aircraft cruised at 11,000 ft. The route to Tanegashima was clear of clouds. About 60 km before Tanegashima, the autopilot was switched from altitude hold to a vertical speed mode for descent. The FO, expecting no hazardous shaking, set engine power to flight idle to maintain 240 kt indicated airspeed (IAS). However, the IAS rapidly increased and approached the maximum operating speed (VMO) of 250 kt. The FO pulled back on the control column while engaging the touch control steering (TCS) button, but the aircraft did not pitch up as expected. The PIC also pulled back and found the nose-up response slower than usual. The flight crew felt strong shaking and heard a VMO exceedance warning. FDR data showed the IAS reached 251 kt for one second.
During the shaking, the pitch angle varied from -2.3° to +6.3° over about one second, and vertical acceleration peaked at +3.3 G. Immediately after, the roll angle changed by 8.5° to the right. The seat belt sign remained off throughout. After the shaking subsided, the PIC observed via cabin camera that a cabin attendant was moving aft with passenger assistance and appeared injured. The PIC decided to return to Kagoshima, notified the company, and requested clearance from air traffic control. The aircraft landed at Kagoshima at approximately 11:45 JST.
Injuries
The cabin attendant, who was providing in-flight service, fell while walking aft near seat row 4. She felt her body floating and then experienced a sudden shaking, resulting in right ankle pain. Unable to stand, she was assisted by a passenger to the aft cabin attendant seat, where she remained until landing. She was transported to a hospital and initially diagnosed with a suspected right anterior talus ligament injury. A follow-up MRI on October 15 revealed a fracture of the posterior malleolus of the right ankle. This injury was classified as serious.
Aircraft and Weather Information
The aircraft, an ATR 42-500 (serial number 1215, manufactured December 29, 2016), sustained no damage. A detailed examination found no abnormalities related to the turbulence encounter. The aircraft's weight and balance were within limits. No flight control system failures were recorded.
Weather conditions were influenced by Typhoon No. 19, located off the Tokai region, with a central pressure of 945 hPa and maximum winds of 85 kt. Isobars around Kyushu were slightly dense. An hourly atmosphere analysis at 11:00 on the accident day showed no vertical wind shear (VWS) exceeding 6 kt per 1,000 ft in the vicinity of the accident site. No pilot reports (PIREPs) near the accident site were filed before the event.
Additional Information
According to the company's Aircraft Operating Manual, VMO is defined as 250 kt, and exceeding it triggers an alarm. The FDR recorded the VMO exceedance for one second. Additionally, during the return flight at around 11:30:43 at 8,000 ft, a vertical acceleration of +1.6 G was recorded near the accident site.