Incident Overview
On July 17, 2017, at approximately 16:30 UTC, a flight instructor and a student pilot conducted pre-start inspections on a Robinson R44 Raven I helicopter at the Bukowina Tatrzańska landing site. After starting the engine, but before engaging the clutch, the crew heard a metallic, cyclic scraping sound from the rear of the fuselage. The instructor immediately shut down the engine.
Inspection and Findings
Following a second pre-flight inspection, the crew attempted another engine start and again heard the metallic scraping sound, prompting another shutdown. The event was recorded in the pilot's daily log, and the instructor notified the Part 145 maintenance organization. Upon removing the fan assembly, technicians found loose screws securing the cone to the fan assembly. The screws showed intact factory-applied paint, indicating no prior maintenance intervention or tampering. Additionally, corrosion was observed on the fan and at the mounting points of the fan to the cone shaft, as well as on the rear wall of the fan.
Manufacturer Response
The removed fan assembly was sent to the manufacturer. On November 21, 2017, the operator received a report from the manufacturer stating: "a crack in the fan cone was detected as a result of loose mounting screws working under permanent vibration conditions." The manufacturer provided a replacement fan assembly under warranty at no cost. The helicopter was subsequently returned to service. No injuries occurred during the incident.