Flight control system failure led to Mutiny Bay crash that killed 10, NTSB says

The NTSB said a failure in the flight control system on the de Havilland DHC-3 led to the deadly 2022 crash that killed 10 people. The failure of a single component of a critical flight control caused the plane to enter into an unrecoverable, near-vertical descent into the water. The NTSB has issued an urgent recommendation to DHC-3 owners and operators, requiring an immediate one-time inspection of the horizontal stabilizer actuator.RELATED STORIES:NTSB opens public docket on Mutiny Bay crash that killed 10NTSB preliminary report released on Mutiny Bay crash that killed 1010 people believed dead following a float plane crash in Mutiny Bay, WashingtonOn Sept. 4, 2022 a float-equipped de Havilland DHC-3 plane was on a scheduled passenger flight with one pilot and nine passengers. The plane was flying between two seaplane bases when it crashed into Mutiny Bay near Freeland, Washington. The plane sank in about 200 feet of water and the wreckage took weeks to recover. The NTSB recovered about 85 percent of the aircraft from the ocean floor and took 17 dives and 26 hours of bottom time. Days after the investigators began the examination of the wreckage, it was found that the actuator that controls the pitch of the plane had been disconnected from a control linkage, making it impossible for the pilot to control the airplane's pitch. This evidence led the NTSB to conclude that flight control failure happened before the crash, not as a result of it. Investigators found that the horizontal stabilizer actuator had separated into two pieces as a result of unthreading, resulting in an urgent safety recommendation to the FAA and Transport Canada on Oct. 26. 2022. During the examination of the wreckage, it was found that the clamp nut which attaches to the top eye end and bearing assembly of the horizontal stabilizer actuator, also known as trim jack assembly, to the actuator barrel had unscrewed from the barrel. The circular wire lock wing, designed to prevent the clamp nut from unscrewing, was missing. A missing or improperly installed lock ring can result in a reduction of loss of pitch control during flight, although it is not known if the lock ring was in place before the crash or part of the 15 percent of the wreckage not recovered. When the plane's design was certified by the FAA in 1952 there was no requirement for a secondary locking device to secure the flight control linkages. In 1996, regulations were amended to require all new aircraft to have a secondary locking device, if the loss of the first device would prevent a safe flight and landing. "We're calling on the Federal Aviation Administration and their Canadian counterparts to eliminate the safety vulnerability identified by NTSB investigators, so this kind of tragedy never happens again," NTSB Chair Jennifer Homendy said.Fuselage view from front right As a result of the investigation, the NTSB is urging the FAA and Transport Canada to require DHC-3 operators to install a secondary retention device to prevent a single point of failure in the flight control system. Additional recommendations were sent to the agencies pertaining to the crash and subsequent findings. The NTSB also sent recommendations to the current type certificate holder Viking Air. "The Mutiny Bay accident is an incredibly painful reminder that a single point of failure can lead to catastrophe in our skies," Homendy said. "To adequately protect safety, we must build in the necessary redundancies across the entire aviation system."