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S-61N fatal accident in Hawaii linked to improper maintenance


The U.S. National Transportation Safety Board (NTSB) said last year’s fatal crash of a Sikorsky S-61N in Kekaha, Hawaii, may have been caused by improperly installed front and rear main servos by maintenance crews.

At the time of the crash, the aircraft was being used to recover inert training torpedoes from the Pacific Ocean.National Transportation Safety Board photoAt the time of the crash, the aircraft was being used to recover inert training torpedoes from the Pacific Ocean.National Transportation Safety Board photo
At the time of the crash, the aircraft was being used to recover inert training torpedoes from the Pacific Ocean.National Transportation Safety Board photo

In the NTSB’s final report on the Feb. 22, 2022, crash, investigators added that the company’s quality control staff failed to notice improper installation before certifying the helicopter for flight, leading to the accident.

The aircraft (registration N615CK) is owned by Croman Corporation and was flying under contract with the U.S. Navy at the time of the accident. Its mission is to locate and recover a training torpedo in open water and then hoist it back to the Barking Sands Pacific Missile Range (PMRF).

On the way back to the PMRF, multiple witnesses saw the helicopter cross the shoreline and begin a shallow left turn as it turned north into the prevailing wind. When approaching the landing site, the helicopter stopped turning and flew northeast. About 200 feet above the ground, it gradually tilted downward and began to crash nose-first in a near-vertical attitude. A post-crash fire destroyed much of the cockpit and passenger cabin. Both pilots and two crew members were seriously injured.

NTSB investigators later determined that the clevis end of the flight control fore/aft servo input link was still connected to the flight control fore/aft crank located near the main gearbox. However, the rod end is only partially connected to the front/rear servo input clevis, and its bolt is mostly out of its normal mounting position.

The front/rear main servo system of the accident aircraft.National Transportation Safety Board photoThe front/rear main servo system of the accident aircraft.National Transportation Safety Board photo
The front/rear main servo system of the accident aircraft.National Transportation Safety Board photo

Since there was no evidence of breakage or deformation, it was determined that the bolt may have been displaced from its normal position during the accident flight due to a missing restraining nut and cotter pin.

This results in uncommanded inputs to the fore/aft servos, resulting in a nose-down attitude of the helicopter and the crew being unable to control its pitch attitude.

Between December 17 and 29, 2021, the helicopter underwent multiple maintenance procedures.

The NTSB concluded in its report that the accident may have been caused by maintenance personnel failing to properly install the front/rear main servos and secure them with the correct hardware.



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