Aircraft and Flight Background
On June 30, 2006, a Cessna 560 (Citation V), registration JA8576, operated by the Yomiuri Shimbun Tokyo Headquarters, took off from Hiroshima Nishi Aerodrome at 16:20 JST on a corporate flight bound for Tokyo International Airport. The aircraft was carrying five persons: the pilot in command (PIC), the first officer, and three corporate passengers (designated Passenger A, Passenger B, and Passenger C). The flight plan was filed under instrument flight rules (IFR) with a cruising altitude of 27,000 ft and an estimated flight time of 1 hour 50 minutes.
Accident Sequence
At around 17:50 JST, while the aircraft was on approach to Tokyo International Airport over Tokyo Bay, approximately 15 km east of the airport, the aircraft experienced a sudden vertical jolt. According to the PIC, the DME indication was 7.8 nm, speed was approximately 185 kt, and altitude was 2,000 ft. The autopilot was engaged. The PIC and first officer both reported that the shaking was sudden and without warning. The PIC described it as a one-time vertical jolt; the first officer characterized it as moderate severity. The PIC noted that preceding aircraft were in the vicinity, and the approach was being flown with caution due to potential wake turbulence. After the incident, the aircraft continued the approach and landed at 17:55, arriving at the hangar at 17:59.
Injuries and Damage
Passenger B, who was seated with seatbelt fastened but without shoulder harness, reported that the violent up-and-down shaking caused his head to hit the cabin ceiling, followed by a hard impact into the seat. He experienced severe pain in his upper and lower back. After landing, he was assisted off the aircraft and subsequently sought medical treatment. A hospital examination diagnosed a possible broken vertebrae; detailed examination on July 3 confirmed a vertebral body fracture in the lower middle portion of the back. Surgery was performed on July 4, and Passenger B was discharged on July 19. Passenger A, a mechanic, noted that two ashtray lids flew off, and a plastic basket in the tail cone baggage compartment had one oil can displaced outside. Post-flight inspection revealed no other abnormalities. The PIC and first officer, both with seatbelts and shoulder harnesses fastened, did not hit the ceiling, though the first officer's head nearly contacted it.
Investigation
The Aircraft and Railway Accidents Investigation Commission (ARAIC) initiated an investigation on July 4, 2006, assigning an investigator-in-charge and two investigators. The National Transportation Safety Board (NTSB) of the United States, as the state of design and manufacture, designated an accredited representative. Interviews and aircraft inspections were conducted on July 4, with follow-up interviews on July 25 and 28. Comments were obtained from parties relevant to the cause and from the participating state. The investigation focused on the flight history and statements from the crew and passengers. The cause of the turbulence was not explicitly determined in the provided source; crew statements suggested wake turbulence as a likely cause, but the investigation report does not state a final probable cause.