What happened
On November 6, 2007, at approximately 11:32 local time, an Mi-8T helicopter departed from the Brandensteinsebene airfield near Coburg, Germany, to perform a ferry flight to Straubing. The helicopter was performing a heavy-lift operation, transporting a Piper Malibu as an external sling load. The aircraft, which had previously sustained landing gear damage, had been temporarily repaired by a maintenance facility to facilitate this transport.
The load configuration involved three steel cables—one on each side of the main landing gear and one around the tail—converging at a central node. A single main cable connected this node to the helicopter's external cargo hook, suspending the aircraft approximately 20 meters below the helicopter. Approximately 16 minutes into the flight, witnesses observed portions of the Piper Malibu's right wing breaking away and flying off. Simultaneously, the aircraft detached from the helicopter's sling and plummeted from an altitude of 200 to 300 meters, impacting the ground nose-first. The helicopter crew landed the helicopter safely in the immediate vicinity of the crash site.
The investigation
The BFU investigation focused on the mechanical failure of the lifting assembly. Investigators recovered the three attachment cables, the central node, and the main cable at the impact site. The examination revealed that the upper end of the main cable had completely slipped out of the eye terminal, which served as the interface to the shackle. The end of the cable was found unraveled for a length of approximately two meters, while the eye terminal and shackle remained attached to the helicopter's cargo hook.
Findings
- The primary cause of the accident was the failure of the main cable to remain secured within the eye terminal.
- The 16 mm diameter steel cable, which featured seven main strands, had been originally swaged into the eye terminal.
- While a cable of this specification should theoretically possess a breaking strength of approximately 16,500 kg, the connection failed during flight.
- The flight occurred in unstable maritime air with gusty westerly winds, though the mechanical failure of the terminal was the decisive factor in the detachment.