Accident Overview
On June 29, 2020, at approximately 09:30 Japan Standard Time, a Fuji-Bell 204B-2 helicopter, registration JA9383, operated by Nakanihon Air Service Co., Ltd., sustained damage during landing at Takaoka operation site in Fukusaki-cho, Kanzaki-county, Hyogo Prefecture. The helicopter was on a ferry flight from Nara Prefecture Heliport with four people on board, including the pilot and three mechanics. No injuries were reported.
Flight History
According to pilot and mechanic statements, the helicopter took off from Nara Prefecture Heliport at around 08:49 and flew at a pressure altitude of approximately 2,000 ft. After passing north of Osaka International Airport, it descended from the east side of the operation site, made a left turn, and approached from the west. During the final approach from the southwest at an altitude of about 40 ft above ground level, the pilot heard a "Kyuin, Kyuin, Kyuin" sound from the rear, which changed to a continuous "bang, bang, bang." The torque meter fluctuated between 20 and 40 psi. The mechanic identified the sounds as engine surging. The pilot and mechanic decided to land vertically. When the pilot lowered the collective pitch control, the helicopter descended rapidly and made a hard landing. After landing, the engine was still running and the "ENG CHIP DET" warning light was illuminated. The pilot shut off the fuel and stopped the engine. A video taken by a witness 30 m north of the touchdown site showed the descent sequence.
Damage to Aircraft
The helicopter was substantially damaged. Primary structural components of the lower fuselage were buckled, including cross tube attachments. The landing gear cross tubes extended outward by approximately 10 cm, and the left and right steps attached to the landing gear were damaged with contact marks on the cross tube. The speaker mounted in the center of the forward cross tube fell and was damaged. The ELT activated upon ground impact. The engine exterior showed no deformation or damage, but the exhaust duct was discolored. A large amount of engine oil was leaking at the bottom of the compressor.
Engine Investigation
A teardown investigation of the engine was conducted at the manufacturer's facility. The axial compressor first stage had one blade fractured near the blade platform. All other blades exhibited impact damage, missing material, bent airfoils in the direction opposite of rotation, and blade tip rub and roll-over. No cracks were found in other compressor blades. The fracture surface of the broken blade was examined. No other engine components showed anomalies beyond those related to the hard landing.
Site and Weather Conditions
The accident site at Takaoka operation site had fields to the east and west, a wooded hill to the south, and construction vehicles parked on the north side of a landing strip built with construction road surface covering plates. Weather observations from a nearby station at the time of the accident recorded an east-southeast wind at 0.8 m/s, temperature 24.8°C, and no precipitation. The pilot and a witness reported wind as almost calm.