What happened
On April 3, 2024, a Kaman K-1200 helicopter was performing an external load operation near Föritztal, Germany. The mission involved using a specialized lifting system, known as a Heligrip, to remove trees damaged by drought from a steep slope. The aircraft was equipped with a rigid spreader bar assembly designed to stabilize the load.
During the takeoff phase to pick up the Heligrip, which was secured on a trailer, the pilot attempted to lift the load vertically. However, the helicopter did not move toward the attachment point as intended. Instead, the rigid nature of the spreader bar caused the load to pull the helicopter's hook sideways. This created a pivot point that induced a rotation around the vertical axis and a roll around the longitudinal axis, similar to a dynamic rollover. The force was sufficient to tear the Heligrip's support cradle from its trailer, dragging the entire assembly behind the aircraft. The pilot attempted to increase power to gain time for an emergency release, but the aircraft lost control and struck the ground approximately 60 meters from the takeoff site. The pilot sustained minor injuries.
The investigation
The BFU examined the aircraft, the external load system, and the meteorological conditions at the time of the accident. The investigation focused on the mechanics of the spreader bar assembly and the pilot's reaction to the sudden lateral forces. Investigators also reviewed the operator's safety management systems and risk assessments regarding the use of the experimental Heligrip system.
Findings
- The primary cause of the loss of control was the restraint of the helicopter caused by the rigid spreader bar assembly.
- The spreader bar was deployed in a fully extended, straight configuration, which left virtually no margin for error or movement during the pickup.
- The Heligrip's gripper was closed, further limiting the system's flexibility.
- The pilot's reaction—increasing collective pitch—was identified as an inappropriate response that likely accelerated the rollover rather than preventing it.
- While wind gusts were present, they were well within the aircraft's demonstrated operational limits and were not a primary cause.
- The external load system was still in a testing phase, and the operator's risk analysis had underestimated the danger of the helicopter becoming tethered to the load.