A de Havilland DHC-3 Otter floatplane on a scheduled flight between two seaplane bases abruptly entered a near-vertical 9,500-fpm descent and stuck the water in Mutiny Bay near Freeland, Washington, U.S., killing the pilot and all nine passengers. The airplane sank to the bottom of the bay and was destroyed.
The U.S. National Transportation Safety Board (NTSB) said in its final report on the Sept. 4, 2022, accident that the probable cause was the failure of a critical flight control system.
The board cited “the in-flight unthreading of the clamp nut from the horizontal stabilizer trim actuator barrel due to a missing lock ring.” That failure caused the horizontal stabilizer to move to “an extreme trailing-edge-down position, rendering the airplane’s pitch uncontrollable,” the report said.
“If a lock ring is not present to secure the actuator barrel and the clamp nut together, they can become separated, and the actuator would not be able to control th…
