AugustaWestland AW119MKII near Philadelphia, PA — 2020-03-21

Probable cause

The in-flight failure of the lower left side of the engine cowling due to the mechanic’s improper installation of the fasteners, which resulted in the cowling impacting all four main rotor blades.

NTSB narrative

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.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Maintenance should have ensured all fasteners were properly secured before the flight.

NTSB coding

• Part(s) separation from AC · Approach
• Maintenance

Evidence available

• Photos
• 3 docket documents

Docket documents3

• PILOT/OPERATOR AIRCRAFT ACCIDENT REPORT, NTSB FORM 6120.1form
• NTSB SUMMARY OF FINDINGSother
• PHOTOSphotos

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