Investigation Summary
The accident flight was the pilot's second trip of the day, consisting of multiple legs through the San Juan Islands. While en route to Renton at approximately 1,000 feet, the aircraft suddenly pitched up slightly before entering a near-vertical, high-speed nose-down descent. Witnesses described the plane spiraling or rotating before impacting the water at high velocity, which resulted in the total disintegration of the airframe. Some witnesses reported hearing a 'loud explosion,' which investigators later clarified was the sound of the high-speed impact with the water rather than an in-flight event. The wreckage settled at a depth of approximately 190 feet. Recovery efforts led by the NTSB and the U.S. Navy retrieved the horizontal stabilizer trim actuator, which was found separated into two pieces. The investigation revealed that the clamp nut had completely unthreaded from the actuator barrel. This specific assembly is secured by a circular wire lock ring; however, the lock ring was not found in the wreckage, and wear patterns suggested it had been missing for some time, allowing vibrations and normal operation to gradually unscrew the nut. The discovery prompted an NTSB campaign to ensure this vulnerability is fixed before tragedy strikes again.
Final Conclusions
The NTSB determined the probable cause was the loss of pitch control due to the unthreading of the clamp nut from the horizontal stabilizer trim actuator barrel. This occurred because the required lock ring was missing, likely due to a maintenance error during a previous assembly. The separation allowed the horizontal stabilizer to move to an extreme trailing-edge-down position, rendering the aircraft's pitch uncontrollable. The board also noted the lack of a redundant design in the DHC-3 pitch trim system, which allowed a single point failure of a small component to result in a catastrophic loss of the aircraft.
Video Analysis
Recent Air Crash Leads to Urgent Aviation Safety Recommendation — An analysis of the 2022 Mutiny Bay DHC-3 crash, focusing on the recovered wreckage and the critical failure of the horizontal stabilizer actuator assembly.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Jason Winters. Total hours as of May 31, 2022. He had been flying the DHC-3 since 2017 and was the company's primary Otter pilot.
Systems & Failure Modes
Horizontal Stabilizer Trim Actuator
A jackscrew-style mechanism that adjusts the angle of the horizontal stabilizer to trim the aircraft's pitch.
Actuator Lock Ring
A small wire ring designed to fit into a groove and prevent the clamp nut from unthreading due to vibration.
Interesting Facts
- 01The aircraft was the last DHC-3 Otter ever built by de Havilland Canada, manufactured in 1967 with serial number 466.
- 02Prior to its US registration, the aircraft was registered in Canada as C-FVQD; this registration was cancelled in November 2013, and the aircraft was exported to the United States in March 2014.
- 03The horizontal stabilizer actuator was found in two pieces because the clamp nut had fully unthreaded from the barrel.
- 04A wire lock ring, which is the only mechanism preventing the nut from unscrewing, was missing from the assembly.
- 05The aircraft had undergone a 100-hour inspection just three days before the accident, on September 1, 2022.
- 06The impact was so severe that witnesses described the plane as 'disintegrating' upon hitting the water.
- 07The aircraft was not equipped with, nor required to have, a flight data recorder (FDR) or cockpit voice recorder (CVR).
Safety Actions & Advisories
Urgent Inspection Recommendation
Source ↗The NTSB issued an urgent recommendation for all DHC-3 operators to visually inspect the stabilizer actuator to ensure the lock ring is present and properly seated.
Viking Air Service Letter
The type certificate holder issued a service letter requiring immediate inspection of the horizontal stabilizer actuator assembly for all DHC-3 Otters.
Known Controversies & Unanswered Questions
Single Point of Failure Design
Reference ↗Legal and safety experts questioned why the DHC-3 pitch trim system lacked redundancy, drawing parallels to the Alaska Airlines Flight 261 crash where a single jackscrew failure also led to a catastrophic loss of control.