What happened
On June 19, 2019, an Aerospatial AS355F2, registered JA6697, was conducting a news coverage flight from Tokyo Heliport. While flying at approximately 2,100 feet near Aikawa-cho, Kanagawa Prefecture, the pilot experienced a sudden boom and vibration. The left engine (No. 1) immediately lost rotation speed, and the pilot observed the generator and automatic restart caution lights illuminate.
Recognizing the engine had shut down, the pilot executed emergency procedures. Due to a significant increase in power demand on the remaining right engine, the pilot performed a controlled, preventive landing on the riverbed of the Nakastre River to avoid further complications. There were no injuries during the incident.
The investigation
The JTSB investigation focused on the internal damage to the No. 1 engine. A teardown inspection revealed that fragments from the compressor had penetrated the engine casing, creating 11 outward-facing cracks and causing significant deformation to the compressor case. The investigation examined the engine's maintenance history, noting that the engine had previously undergone repairs for a broken bearing housing stud and corrosion on the compressor case in 2017. Investigators also reviewed the operating environments of the engine, which had been based in both mountainous and coastal regions, and the storage conditions of the engine as a spare unit prior to its installation in JA6697.
Findings
- The primary cause of the engine failure was the fracture of the second-stage compressor blades.
- This fracture was likely triggered by corrosion that had weakened the structural integrity of the blades.
- While no foreign object damage (FOD) was found, corrosion was present on the leading edges of the first-stage blades.
- It is probable that residual corrosion from previous repairs was not fully eliminated, and inadequate water rinsing after flights or during storage allowed the corrosive environment to further degrade the components.
- The investigation noted that while visual inspections were performed, a more rigorous focus on identifying early signs of corrosion on accessible blade edges might have prevented the failure.