The improper installation of a key helicopter part was the likely cause of the Feb. 22, 2022, fatal crash at Kauai’s Pacific Missile Range Facility Barking Sands, the National Transportation Safety Board said this week in a final report on the incident.

Two pilots and two crew members were killed in the crash of the Sikorsky S-61 helicopter under contract to the Navy.

The flight’s mission involved locating a training torpedo in the open waters, retrieving the torpedo using a recovery basket/cage system, then returning the torpedo by sling load to Barking Sands.

As the helicopter was returning to the base at about 10:20 a.m., witnesses saw it make a couple of turns and then drop to the ground nose-down, the report said.

In an examination of the wreckage, an investigator found the “fore/aft primary servo” without a nut and cotter pin, which likely led to a condition that allowed the aircraft to lose control.

“The mechanic who installed the fore/aft servo input link to the fore/aft primary servo likely failed to correctly install the attaching hardware,” the report said, adding that the company’s certified inspector failed to notice the error, too.

Those who died in the crash were pilots Daniel Maurice, 64, and Patrick Rader, 55, and crew members Matthew Haider, 43, and Erika Teves-Valdez, 42. Maurice was a resident of Lyle, Wash., while the others lived on Kauai.

The helicopter was owned and operated by Oregon-based Croman Corp., which employed all four victims and has provided air support services at the Pacific Missile Range Facility since 2007.