U.S. investigators say a mechanical issue may have caused the seaplane crash that killed 10 people off an island in Washington state last month.
The most recent overhaul of the plane’s horizontal stabilizer actuator was completed April 21. The lock ring was not found with the wreckage, but several of the holes drilled in the clamp nut to accept the lock ring were damaged “such that they would not allow for the full insertion of the lock ring.”
The NTSB and the Transportation Safety Board of Canada have asked that the manufacturer draft instructions for all operators of DHC-3 aircraft to inspect the actuator to ensure that the lock ring is properly installed to prevent unthreading of the clamp nut. Crews using remotely operated vessels and cranes recovered the majority of the plane’s wreckage from the sea floor more than 150 feet below the surface in late September.