The National Transportation Safety Board on Thursday announced an “urgent safety recommendation” for operators of the type of floatplane that crashed off Whidbey Island in September, killing all 10 people on board.
NTSB recommends that the Federal Aviation Administration and Transport Canada require all operators of the De Havilland Canada DHC-3 plane to inspect its horizontal actuator lock ring.
“Immediate action needs to be taken to inspect the actuator of DHC-3 airplanes, of which 40% operate in the United States, to prevent a similar tragedy from happening,” said NTSB Chair Jennifer Homendy. “NTSB is issuing this urgent recommendation as a result of a significant finding made by NTSB investigators.”
Investigators had previously identified concern with the horizontal stabilizer actuator, a piece of the tail that provides stability to the up-and-down flight of the aircraft.
A pilot can manipulate the actuator with the pitch trim wheel in the cockpit, which manipulates the actuator with control cables that extend or retract the length of the actuator, which allows the pilot to relieve elevator control force pressure.
According to investigators, the actuator was found separated, and an examination of the threads inside the barrel and the threads on the clamp nut revealed the two pieces separated by unthreading, not by the impact.
The upper portion was found attached to the horizontal stabilizer, while the bottom portion was found attached to its mount in the fuselage.
According to investigators, a circular wire lock ring should be used to keep the two parts from unthreading. Through examination of the wreckage, investigators found that the circular wire lock ring was not present.
An unthreaded actuator would result in a free-floating horizontal stabilizer, allowing it to move uncontrollably on its hinge, resulting in a possible loss of airplane control.
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