What happened
On May 21, 2010, an Mi-8T helicopter, registration OK-XYC, was performing aerial work to transport cooling towers between Letenská pláň and a site near the Vltava River in Prague. During the transport of the second load, a wooden timber measuring approximately 1m x 0.1m x 0.1m detached from the underside of the cargo and fell into the Vltava River near Čechův Bridge.
The timber had been placed under the cooling towers by ground personnel to facilitate handling and prevent contamination of the cargo. The flight crew did not notice the object falling, and the subsequent transport of the remaining loads proceeded without further incident. No injuries were reported, and no damage occurred to the aircraft.
The investigation
The ÚZPLN investigation examined the preparation of the cargo, the sling load procedures, and the actions of the ground crew. The investigation established that the cooling towers had been placed on wooden timbers at the request of the ground workers to assist with stability and cleanliness. The investigation also reviewed the roles of the ground crew, specifically the lead slinger, and the adherence to the established technological protocol for the mission.
Findings
- The primary cause of the incident was the failure of the lead slinger to perform a thorough inspection of the underside of the load after it was lifted to a height of approximately 2 meters.
- The ground crew and the lead slinger failed to notice that one of the wooden timbers had become lodged in the bottom of the cargo during the initial lift.
- The lead slinger's preparation for the aerial transport was inadequate, specifically regarding the verification of the cargo's underside for foreign objects.
- The inspection of the underside of the load was not performed in accordance with the approved technological procedure.
Safety action
- The air operator's operating manual should be updated to include specific tasks and responsibilities for individual personnel involved in sling load operations.