ERA20CA135

Factual narrative

The pilot and the flight test engineer had just completed a production test flight of the helicopter and were preparing to land when the lower section of the left side of the engine cowling folded back and struck all 4 main rotor blades and made contact with all 4 main rotor blades at some point prior to the rotor stopping, resulting in substantial damage. According to the operator/manufacturer, none of the fasteners on the left side of the cowling remained attached and 3 of the fasteners were missing.Prior to the flight, the pilot observed that the fasteners attaching the generator duct to the right side of the same cowling appeared long and reported it to maintenance. No anomalies were observed with the fasteners attaching the cowling tothe airframe. Maintenance then removed the one-piece engine cowling and a mechanic replaced the generator duct fasteners before reinstalling the cowling with the help of another mechanic. The mechanic said he specifically fastened each of the fasteners on the cowling himself and did a 100% check of each fastener after the cowling was installed. Once the cowling was reinstalled a quality inspector visually inspected the engine cowling fasteners. He did not observe any anomalies and signed off that the work had been completed. Prior to the accident flight, the flight test engineer performed another preflight inspection of the helicopter and did not observe any obvious issues with any of the cowling fasteners. The helicopter then departed and flew for about an hour before the cowling folded back. Postaccident examination of the cowling by the operator/manufacturer revealed no evidence of any preaccident discrepancies with the fasteners/cowling, or the design and conformity of the helicopter structure. The pilot and the flight test engineer were completing a production test flight of the helicopter. A review of a surveillance video showed that, as they were preparing to land, the lower section of the left side of the engine cowling folded back and struck all four main rotor blades, which resulted in substantial damage to the blades. According to the operator/manufacturer, postaccident examination of the helicopter revealed that none of the fasteners on the left side of the cowling remained attached and that three of the fasteners were missing. No evidence of any preaccident discrepancies with the fasteners, the cowling, or the design and conformity of the helicopter structure was found. According to the manufacturer/operator, before the flight, the pilot reported to maintenance personnel that he had seen that the fasteners attaching the generator duct to the right side of the same cowling appeared long. Maintenance personnel then removed the one-piece engine cowling, and a mechanic then replaced the generator duct fasteners and reinstalled the cowling with the help of another mechanic. The mechanic said he specifically fastened each of the fasteners on the cowling himself and checked all the fasteners after the cowling was reinstalled. Once the cowling was reinstalled, a quality inspector visually inspected the engine cowling fasteners. He did not see any anomalies and signed off that the work had been completed. The flight test engineer performed another preflight inspection of the helicopter and did not note any issues with any of the cowling fasteners. It is likely that the mechanic did not properly install the cowling fasteners before the flight, which resulted in the cowling coming loose and striking the main rotor blades. Source: NTSB Aviation Accident Database Retrieved: 2026-02-12

NTSB Findings

FAA avdata. C = Cause, F = Factor.

• C Aircraft-Fluids/misc hardware-Misc hardware-Fasteners-Incorrect service/maintenance - C
• C Personnel issues-Task performance-Maintenance-Installation-Maintenance personnel - C
• C Aircraft-Aircraft power plant-Engine (turbine/turboprop)-(general)-Failure - C