What happened
On September 4, 2019, an AS350 B3 helicopter, registration D-HAUE, operated by Helibravo – Aviação Lda., was preparing for a firefighting mission at the Pampilhosa da Serra CMA in Portugal. During the take-off sequence, the pilot noticed a sudden increase in engine power immediately after selecting the flight command. This surge caused the aircraft to oscillate and rotate 90 degrees clockwise.
As the aircraft rose to approximately one meter, the pilot was unable to counteract a low tail attitude. The helicopter descended, striking the ground hard with the rear right skid and the tail rotor. The impact caused the aircraft to rotate around its longitudinal axis, eventually resulting in the main rotor striking the ground. The aircraft came to rest on its right side, approximately three meters from the initial contact point. While all occupants were wearing seat belts, one passenger was briefly trapped near the right-side door during the evacuation. There were no fatalities, though one passenger sustained minor injuries.
The investigation
The GPIAAF investigation focused on the engine performance and the operational differences between aircraft models in the operator's fleet. Analysis of the Engine Vital Management System (VEMS) confirmed two peaks in main rotor speed exceeding 448 rpm, which significantly surpassed the certified maximum limit of 390 +4/-5 rpm.
The investigation also examined the pilot's experience, noting that while the pilot was highly experienced in the AS350 B2 model, this was his first flight at this specific location using the Arriel 2B engine configuration. The investigation highlighted critical procedural differences between the Arriel 2B and the Arriel 2B1 engines, specifically regarding the pre-flight engine start-up and power selection procedures via the twist grip.
Findings
- The primary cause of the accident was a sudden increase in engine power that exceeded certified rotational limits.
- The pilot's recent experience was primarily with the AS350 B2, and he had only 8.25 hours of flight time in Portugal using the specific Arriel 2B engine configuration.
- Significant operational differences exist between the Arriel 2B and Arriel 2B1 engines regarding the twist grip position (FLIGHT/VOL vs. IDLE) and the engine governor (single-channel DECU vs. dual-channel EBCAU1).
- There was no evidence of a lack of medical fitness or any medical condition affecting the pilot's performance.
- The aircraft sustained substantial damage to the engine, transmission, main rotor, and tail rotor.
Safety action
Following the accident, the operator, Helibravo – Aviação Lda., implemented a new safety procedure for mission departures. Ground staff are now required to maintain continuous visual contact with the pilot and only signal readiness with a "thumbs-up" once both parties have confirmed they are ready for flight.
The GPIAAF issued safety recommendation PT.SIA 2019-008, advising the operator to ensure all pilots are thoroughly trained on the specificities of different engine configurations within their fleet and to work toward standardizing the AS350 B3 fleet to mitigate risks associated with non-standardized equipment.