What happened
On September 5, 2019, at 15:24 UTC, an Airbus Helicopters AS350 B2, registration CS-HFT, was engaged in an aerial firefighting mission near Sobrado, Valongo, Portugal. The aircraft, operated by Helibravo, was performing water drops to combat a forest fire when it struck high-voltage power lines. The collision resulted in a crash that led to a post-impact fire.
The investigation
The GPIAAF investigation examined the mission planning, risk assessment, and the technical aspects of the aircraft's crashworthiness. The investigation focused on the flight path relative to the national energy distribution lines and the effectiveness of the aircraft's fuel system in protecting occupants during a post-crash fire. The investigators also reviewed the management of aerial assets by the Portuguese Air Force (FAP), which is responsible for managing firefighting resources.
Findings
- The primary cause of the accident was the collision with high-voltage power lines during the firefighting maneuver.
- The aircraft's fuel storage system design, which met certification standards at the time of its original type certification, contributed to the severity of the post-impact fire.
- The aircraft was equipped with an Arriel 1D1 engine, which did not include certain modern overspeed protection modifications found in newer variants.
- The mission involved high-risk maneuvers near artificial navigation obstacles, specifically medium and high-voltage electrical lines.
Safety action
- A safety recommendation was issued to the FAP to establish operational limits for aerial firefighting, ensuring aircraft do not operate near electric power lines where the Water Protection System (WPS) is ineffective.
- A non-formal recommendation was issued to all aerial firefighting operators to maintain a safe distance from artificial obstacles to protect both the aircraft and the crew.
- All firefighting operators are alerted to implement procedures ensuring the use of protective helmets by flight crews.
- Safety Recommendation PT.SIA 2020/16 was issued to EASA, recommending the retroactive application of modern fuel tank crash resistance improvements to helicopters used in commercial operations, even if they were certified under older specifications.