What happened
On February 22, 2022, at approximately 10:20 HST, a Sikorsky S-61N helicopter, registration N615CK, crashed at the Pacific Missile Range Facility (PMRF) in Kekaha, Hawaii. The aircraft was operating under a Part 1/33 flight for Croman Corporation, performing a mission for the United States Navy to retrieve inert training torpedoes from the ocean and return them to the facility via sling load.
According to ADS-B data, the helicopter departed PMRF and flew north-northwest to an area 44 miles away. After maneuvering, the aircraft returned south-southeast toward PMRF. As the helicopter approached the facility and crossed the shoreline, it began a shallow left turn into the prevailing wind. As it neared the ordnance recovery clear area (ORCA), the left turn ceased, and the aircraft began traveling in a northeasterly direction.
Witnesses near the site reported that while the helicopter was approximately 200 feet above the ground, it gradually pitched nose-down and impacted the ground in a near-vertical attitude. The crash resulted in 4 fatal injuries for the two pilots and two crewmembers.
The investigation
Investigators examined the wreckage and found the helicopter had come to rest on its left side. The main rotor blades were heavily fragmented, and a post-crash fire consumed much of the cockpit and cabin.
An examination of the flight control system revealed that the fore/aft servo input link remained connected to the bellcrank near the main gearbox. However, the rod end was only partially connected to the fore/aft servo input clevises. The bolt used to secure this connection had mostly backed out of its proper position. While the bolt itself showed no signs of fracture or deformation, the nut, nut-side bushing, washers, and cotter pin were missing.
Maintenance records showed that the fore/aft primary servo had been installed on December 28, 2021, approximately 7.5 flight hours before the accident. During this maintenance period, mechanics from both the operator's base in Oregon and the local PMRF station had performed various actions on the aircraft.