Incident Overview
On July 28, 2024, at approximately 14:55 JST, a privately owned Agusta A109E helicopter (registration JA02KG) experienced a partial failure of its flight control system while flying over Yachiyo Town, Yuki County, Ibaraki Prefecture. The helicopter was performing an operational check of its radio communication device after taking off from an operation site in Yuki City. Two persons were on board: the captain and a mechanic. During a descent, a banging sound was heard and torque from both engines dropped to 1%. The collective pitch lever became unresponsive, and the helicopter could not maintain altitude. The captain declared a state of emergency and executed a forced landing in an unused playground at Higashi Fukita Sports Park.
Flight History
According to the captain's statement and radar records, the helicopter departed from the Yuki Operation Site and conducted radio checks near Sekiyado. While descending from about 2,000 ft over Yachiyo Town, the crew heard a banging sound and both engine torque indicators suddenly dropped to 1%. The cyclic stick and rudder pedals remained functional. At 14:55:39, the captain made a distress call to Narita Tower reporting a power loss. The helicopter descended steeply in a left turn to avoid high-voltage power lines. The captain forgot to extend the landing gear during the forced landing. After landing, the mechanic disembarked and inspected the helicopter. The captain then shut down the engines and main rotor. No injuries were sustained by the occupants, and no fire occurred.
Damage to the Aircraft
The helicopter sustained minor damage. The lower surface of the fuselage and the outer panel of the right side of the aft fuselage had scratch marks. One main rotor blade (red) had a hole and was deformed; two tail rotor blades had dents on the leading edge; the tail rotor drive shaft was broken; and a loudspeaker on the lower fuselage was detached. The structural failure involved the scissors lower link becoming detached from the stud bolts of the upper swashplate; associated cotter pin, nuts, and washers were missing. Additionally, the outer fence of the sports park collapsed in a section about 7 m wide.
Investigation Findings
The Japan Transport Safety Board (JTSB) investigated the serious incident, with participation from accredited representatives of Italy (state of design and manufacture of the helicopter) and Canada (state of design and manufacture of the engine). The helicopter was an Agusta A109E, serial number 11090, manufactured in 2000. The captain held a commercial pilot certificate with type rating for land-multi turbine and had 7,687 hours total flight time. The helicopter's weight and center of gravity at the time of the incident were within allowable limits.
Examination of the main rotor scissors revealed that the lower link had detached from the upper swashplate. The scissors assembly is an essential component that transmits rotation from the main rotor hub to the upper swashplate. According to the helicopter manufacturer, such a detachment is considered a catastrophic failure with no emergency procedures in the flight manual to address it.
Maintenance records indicated that between April 12 and June 6, 2024, periodic checks were performed by Mechanic B at Iwai Heliport. During those checks, the scissors linkage was replaced because the gap measurement was out of tolerance. Inspection of the cotter pin installed after replacement showed that it was not sufficiently bent or tightly secured, and it lacked anticorrosive coating.
Meteorological Conditions
At the time of the incident, weather data from the Automated Meteorological Data Acquisition System (AMeDAS) station in Shimotsuma (about 4 km from the landing site) recorded a southeast wind of 1.2 m/s, temperature 34.2°C, and sunshine in the previous 10 minutes.
The forced landing site exhibited a linear trench on the ground, collapsing of the outer fence, and paint transfer matching the helicopter's color.