What happened
On February 4, 2019, at 11:21 LMT, a medical rescue crew from Olsztyn was dispatched for a HEMS (Helicopter Emergency Medical Service) mission to the village of Grom. The crew conducted the approach following VFR (Visual Flight Rules) procedures. During the landing phase, the rotor wash lifted a large piece of transparent plastic film that had been previously obscured by accumulated snow. The debris was blown toward the aircraft's tail rotor.
Upon touchdown, the crew noted an unusual noise emanating from the rear of the aircraft. The commander instructed the crew member to inspect the exterior, who subsequently discovered that the film had become lodged in the fenestron. After shutting down the engines, the pilot identified fragments of the film on the tail rotor drive shaft and the fenestron blades.
The investigation
The investigation focused on the damage sustained by the aircraft's tail rotor assembly. Following the incident, the aircraft was grounded, and a mechanic from Warsaw-Babice arrived to perform inspections. After consulting with the manufacturer, specific inspections were carried out in accordance with service bulletins and maintenance manuals. During this technical review, personnel discovered that the flexible connections of the clutch on the long tail rotor drive shaft had suffered deformation in the form of delamination at all three connection points.
Findings
- The primary cause of the incident was the ingestion of transparent plastic film into the fenestron, which was lifted from the ground by rotor wash after being hidden under a layer of snow.
- The debris caused structural damage to the flexible connections of the tail rotor drive shaft clutch.
- The operator has proposed systemic changes to training protocols regarding landings in unprepared terrain, specifically focusing on identifying potential foreign object debris (FOD) hazards.