SEA01MA163 · Kawasaki KV-107-II

The Kawasaki Vertol KV-107 II rotorcraft had departed the helibase on a non-mandatory test flight requested by the pilot-in-command (PIC) to 'tweak' the rotorcraft's engine synchronization system. The test flight was conducted with the bucket and 150 foot long line attached to facilitate the test procedure. Witnesses reported observing the rotorcraft between 300 and 1,000 feet in altitude and beginning a climb when it began to pitch/roll and descend rapidly. Several witnesses reported seeing the bucket horizontal to the rotorcraft and also caught up in one of the rotors. The aircraft impacted on its right side intact with the exception of its rotor blades. Two of the three forward rotor blades were found 600-900 feet from the ground impact site. The third forward rotor blade, which was broken in half, was found with its outboard section at the ground impact site and the inboard half approximately 100 feet away. All three aft rotor blades were found in close proximity to one another and approximately 400 feet distant from the primary ground impact site. All six blades separated from their root sections in about the same place and a post crash fire destroyed much of the rotorcraft. Post crash examination established control continuity from the cockpit area through the control closet and on to all the associated hydraulic actuators as well as the continuity of the entire synchronization drive shafting. Examination and disassembly of all major components revealed no evidence of any fatigue propagation, disconnects, or characteristics of other time dependent failure mechanisms. All hydraulic actuators underwent an X-ray examination and disassembly and there was no evidence of any blockage or jamming within any of the actuators. The engines were examined and disassembled and the gas generator speed range for both was determined to be between 64.3% and 69.7%, or about 10% above ground idle. There was evidence that the long line cable encountered/impacted the nose gear strut, as well as an aft strut, the forward left side of the fuselage, the forward rotor head rain shield and all three forward rotor blades. It could not be determined whether the cable to rotor interaction was an initiating event or the result of a previous occurrence which allowed the cable to become entangled with the forward rotor blades. The PIC had more than 1630 hours of V-107 rotorcraft time of which more than 670 hours were logged as PIC time. The co-pilot had more than 150 hours of V-107 rotorcraft time none of which was PIC time.

Verbatim NTSB analysis and probable cause from the NTSB dataset