Status: | Accident investigation report completed and information captured |
Date: | Sunday 4 September 2022 |
Time: | 15:09 |
Type: | de Havilland Canada DHC-3T Turbine Otter |
Operator: | Friday Harbor Seaplane Tours |
Registration: | N725TH |
MSN: | 466 |
First flight: | 1967 |
Engines: | 1 General Electric H80 |
Crew: | Fatalities: 1 / Occupants: 1 |
Passengers: | Fatalities: 9 / Occupants: 9 |
Total: | Fatalities: 10 / Occupants: 10 |
Aircraft damage: | Destroyed |
Aircraft fate: | Written off (damaged beyond repair) |
Location: | 3 km (1.9 mls) SW off Freeland, WA ( United States of America)
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Phase: | En route (ENR) |
Nature: | Domestic Non Scheduled Passenger |
Departure airport: | Friday Harbor SPB, WA (FBS), United States of America |
Destination airport: | Renton Airport, WA (RNT/KRNT), United States of America |
Narrative:A float-equipped de Havilland Canada DHC-3T Turbine Otter, N725TH, was destroyed when it impacted the water in Mutiny Bay, Washington. All ten occupants were killed in the accident.
The accident flight departed from Friday Harbor Seaplane Base, Washington, about 14:50 with a destination of Renton-Will Rogers Wiley Post Memorial Seaplane Base, Washington. Track data indicated the airplane flew at an en route altitude of 650 to 975 ft above mean sea level (msl), and the groundspeed was between 115 and 125 knots.
At 15:08:43, the airplane pitched up about 8° and then abruptly pitched down about 58°. The data ended at 15:08:51, when the airplanes altitude was 600 ft msl and the estimated descent rate was more than 9,500 ft per minute.
Witnesses near the accident site reported that the airplane was in level flight before it entered a slight climb, then pitched down in a near-vertical descent. The airplane continued in a nose low, spiraling, near-vertical descent until it impacted water in Mutiny Bay.
The wreckage was located a week later, at a depth of 190 feet.
Probable Cause:
Probable Cause: The in-flight unthreading of the clamp nut from the horizontal stabilizer trim actuator barrel due to a missing lock ring, which resulted in the horizontal stabilizer moving to an extreme trailing-edge-down position rendering the airplanes pitch uncontrollable.
Accident investigation:
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Investigating agency: | NTSB |
Status: | Investigation completed |
Duration: | 1 year and 1 months | Accident number: | DCA22MA193 | Download report: | Final report
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Classification:
Horizontal stabilizer
Loss of control
Sources:
»
AP»
Photo»
NTSB
Follow-up / safety actions
NTSB issued 10 Safety Recommendations
Issued: 27-OCT-2022 | To: FAA | A-22-23 |
TO THE FEDERAL AVIATION ADMINISTRATION: Require all operators of De Havilland Canada DHC-3 airplanes to conduct an immediate one-time inspection of the horizontal stabilizer actuator lock ring in accordance with the instructions in Viking Air Limited Service Letter DHC3-SL-27-001 and report their findings to the Federal Aviation Administration. (Urgent) |
Issued: 27-OCT-2022 | To: Transport Canada | A-22-24 |
TO TRANSPORT CANADA: Require all operators of De Havilland Canada DHC-3 airplanes to conduct an immediate one-time inspection of the horizontal stabilizer actuator lock ring in accordance with the instructions in Viking Air Limited Service Letter DHC3-SL-27-001 and report their findings to Transport Canada. (Urgent) |
Issued: 05-OCT-2023 | To: FAA | A-23-01 |
Require operators of DHC-3 airplanes to install a secondary retention feature on the horizontal stabilizer actuator clamp nut to ensure it remains secured to the barrel in the event the lock ring is not installed or otherwise fails to retain the clamp nut. |
Issued: 05-OCT-2023 | To: FAA | A-23-02 |
Require operators of DHC-3 airplanes to visually inspect both the horizontal stabilizer actuator lock ring and the associated torque seal at an interval that ensures safe flight or until a secondary retention feature is installed. |
Issued: 05-OCT-2023 | To: Transport Canada | A-23-03 |
Require operators of DHC-3 airplanes install a secondary retention feature on the horizontal stabilizer actuator clamp nut to ensure it remains secured to the barrel in the event the lock ring is not installed or otherwise fails to retain the clamp nut. |
Issued: 05-OCT-2023 | To: Transport Canada | A-23-04 |
Require operators of DHC-3 airplanes to visually inspect the horizontal stabilizer actuator lock ring at an interval that ensures safe flight or until a secondary retention feature is installed. |
Issued: 05-OCT-2023 | To: Transport Canada | A-23-05 |
Require operators of DHC 3 airplanes install a torque seal on the horizontal stabilizer actuator clamp nut and lock ring and inspect the torque seal at an interval that ensures safe flight until a secondary retention feature is installed. |
Issued: 05-OCT-2023 | To: Viking Air | A-23-06 |
Develop inspection criteria for maintenance personnel to determine whether the horizontal stabilizer trim actuator lock ring is airworthy or needs to be replaced, to be performed at an interval that ensures safe flight. |
Issued: 05-OCT-2023 | To: Viking Air | A-23-07 |
Notify DHC-3 operators of the circumstances of this accident and instruct them to remove moisture seals that are installed within horizontal stabilizer actuators and are not approved by Viking Air or a regulatory agency. |
Issued: 05-OCT-2023 | To: Viking Air | A-23-08 |
Revise the DHC-3 AMM to include inspection and overhaul procedures for the horizontal stabilizer actuator that specify how many holes can be drilled into the clamp nut and how to determine if the holes are airworthy, a proper torque value for installing the clamp nut, and how to install the lock ring and verify that it is properly seated and functions as intended. |
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This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.