Introduction
On February 10, 2009, a Bell 206L-3 helicopter, registered JA6055 and operated by Shin Nihon Helicopter Co., Ltd., was involved in an accident while conducting a transmission line inspection flight in Minakami-machi, Tone-gun, Gunma Prefecture. The aircraft sustained substantial damage, and both occupants—a pilot in command and a transmission line inspector—suffered serious injuries.
History of the Flight
The helicopter departed from a temporary helipad in Numata City, Gunma Prefecture, at approximately 09:38 Japan Standard Time (JST) for an inspection flight of the Minakami line (Grid A). The flight plan submitted to the Tokyo Airport Office specified VFR flight rules, a cruising speed of 30 knots, and an intended route from Yujuku substation to various points, with a total estimated flight time of 1 hour 10 minutes.
According to statements from the pilot and inspector, after takeoff, they began inspecting Grid A. The pilot reported difficulty identifying tower serial numbers and initially failed to spot the intersecting transmission lines of Grid B. After passing tower 36, the pilot rechecked the route map and then spotted Grid B. He instinctively banked the aircraft to the right, but the helicopter contacted one of the transmission lines of Grid B. The pilot stated that after the contact, the aircraft became briefly trapped, then freed, and subsequently entered an uncontrolled descent, crashing into a nearby mulberry field.
The inspector reported that during the flight, his attention was drawn to foliage near tower 36, and he did not make call-outs regarding obstacles. He noted that the helicopter suddenly began climbing before the wire strike. After the impact, the aircraft banked right, became parallel to Grid B, and then descended leftward to the ground.
The accident occurred around 09:53 JST at the mulberry field near the overhead intersection of Grid A and Grid B (coordinates 36° 42’ 52”N, 138° 57’ 57”E).
Injuries to Persons
The pilot sustained broken lumbar vertebrae. The inspector sustained broken lumbar vertebrae and viscerocranium. Both injuries were classified as serious.
Damage to the Aircraft
The aircraft was destroyed. Specific damage included:
- Fuselage and tailboom: destroyed
- Landing gears: destroyed
- Main rotor blades: one separated, the other destroyed
- Main rotor mast: separated
- Engine: damaged
- Tail rotor blades: separated
Other Damage
One of the transmission lines of Grid B—the lowest line on the west side (Line C)—was cut and hung over Grid A. This caused a power outage lasting approximately four hours, affecting roughly 17,000 households and disrupting two local train operations on the JR Joetsu Line.
Personnel Information
The pilot, aged 35, held a commercial pilot certificate for rotorcraft with a land single-turbine rating. The inspector had approximately 30 years of experience in power grid inspection by helicopter and was familiar with the inspection route.