What happened
On August 6, 1996, at approximately 12:20 PM, an MBB BO105 CBS helicopter, operated by the Hamburg police, crashed into a harbor basin near Neustadt/Holstein during a training mission. The flight was part of an annual exercise for a police diver unit, simulating the rescue of persons from the water using an external load consisting of a rescue net attached to a 6.5-meter line.
During the sixth training flight of the day, the pilot initiated a left turn at an altitude of approximately 50 meters. During this maneuver, the external load began to oscillate violently. The oscillations intensified until the connection cable between the cargo hook and the rescue net made contact with the main rotor. The impact caused three of the four rotor blades to detach from the rotor head, along with the entire tail boom. The aircraft lost all lift, pitched forward sharply, and struck the water nearly vertically. All five occupants on board—the pilot, a flight mechanic, an instructor, and two police divers—were killed in the crash.
The investigation
The BFU investigation focused on the mechanics of the rotor failure and the configuration of the external load. Investigators examined the wreckage, which was recovered from a depth of approximately 5 meters. The investigation included a reconstruction of the wreckage, an analysis of the rotor blades, and an examination of the cargo hook assembly.
Technical analysis of the rotor blades revealed significant damage, including a strike mark on one blade consistent with contact by a wire cable. The investigation also reviewed the pilot's flight experience and the organizational procedures regarding training and external load operations. Investigators found that while the pilot was highly experienced in general helicopter operations, his experience with external load maneuvers was extremely limited due to the rarity of such training exercises.
Findings
The primary cause of the accident was that the connection cable between the cargo hook and the rescue net entered the main rotor after the external load developed uncontrolled oscillations.
Several contributing factors were identified:
- The configuration of the external load, specifically the length of the cable and the shape of the rescue net relative to its low weight, was improper and encouraged unstable swinging.
- The pilot possessed very little experience in conducting operations involving external loads.
- There were no established procedures or standards available to the unit commander for determining the technical requirements or training programs for such specialized maneuvers.
- There was a lack of information exchange with other organizations or police units that had experience with similar rescue systems.
- There was no effective mechanism to ensure the flight mechanic was constantly monitoring the load to provide early warning of oscillations.