Incident Summary
On June 19, 2019, at approximately 17:55 Japan Standard Time, an Aerospatial AS355F2 helicopter, registered as JA6697 and operated by Toho Air Service Co., Ltd., experienced a serious incident while flying over an area near Aikawa-cho, Aiko-gun, Kanagawa Prefecture. The No. 1 engine (left engine) shut down after a single boom was heard, and fragments penetrated the engine casing. The pilot in command (PIC) performed emergency procedures and made a preventive landing on the riverbed of the Nakatsu River in Aikawa-cho around 18:01. No injuries to the three occupants (PIC, mechanic engineer, and press cameraperson) were reported.
Flight History
The helicopter departed from Tokyo Heliport at 17:35 for press and news coverage. The PIC, seated in the right seat, flew at approximately 2,000 ft to the reporting location. Live coverage began around 17:51 while the helicopter maintained about 2,100 ft and 60 kt. At 17:55, the PIC heard a single boom, felt vibration, and observed the GEN and AUTO caution lights for the No. 1 Engine illuminate, with the N1 indication dropping to zero. The PIC recognized an engine shutdown and executed single-engine failure procedures. The No. 2 engine power increased radically, and the PIC lowered the collective pitch lever to avoid exceeding limits. The PIC then decided to make a preventive landing due to limited power availability and selected a clear riverbed site.
Damage Assessment
Post-landing inspection revealed that fragments of the compressor stator vanes and blades penetrated the engine casing. The No. 1 engine, a turboshaft engine (Allison 250-C20F, serial number CAE-840936), sustained internal damage including deformation of the front support, significant damage to the 2nd through 6th stage compressor blades and stator vanes, and 11 outward cracking openings on the compressor case. The combustion chamber, gas producer turbine, and power turbine contained fragments and scratch marks. The No. 2 engine showed no anomalies. The helicopter itself was slightly damaged, with major damage confined to the No. 1 engine.
Additional Information
The helicopter (Aerospatial AS355F2, serial number 5524, manufactured June 17, 1993) had a total flight time of 4,751 hours 24 minutes. The No. 1 engine had been previously installed in another Toho Air Service helicopter (JA9647) where a broken stud for the front bearing housing was discovered in August 2017. After repair, it was installed in JA6697 in January 2019. The weight and balance at the time of the incident were within allowable limits. Meteorological conditions were cloudy with visibility 20–30 km, wind south to southeast at 4–5 kt, and temperature 20–21°C.