NTSB opens public docket on Mutiny Bay crash that killed 10

On Friday the NTSB opened the public docket on the ongoing investigation into the Sept. 4, 2022 crash of a de Havilland DHC-3 Turbine Otter in Mutiny Bay. The public docket contains over 500 pages of documents, photos, videos, maintenance records and witness statements. The investigation is still ongoing and a final report will be released at a later date.

On Sept. 4 a de Havilland DHC-3 (N725TH) was conducting a scheduled CFR Part 135 flight between Friday Harbor, Washington and Renton, Washington. On board was a pilot and nine passengers. This was the pilot’s second trip of the day and each trip included numerous flight legs. The plane departed from Friday Harbor Seaplane Base (W33) for the Renton Municipal Airport (RNT) and data indicates the plane flew a southerly heading before turning south-southeast. While en route the altitude was between 650 and 975 feet above mean sea level and the groundspeed was between 115 and 125 knots.

10 people believed dead following a float plane crash in Mutiny Bay, Washington

The altitude increased to 1,125 feet and the groundspeed reduced to 109 knots when just seconds later the altitude dropped to 875 feet and the groundspeed reduced to 100 knots. Tracking data ended a few seconds later at an altitude of 700 feet and a groundspeed of 55 knots. Witnesses reported the plane in level flight before entering a slight climb and then pitching down in a near-vertical descent. The plane continued in a nose-low, near-vertical descent until impacting the water in Mutiny Bay. All nine passengers and the pilot were killed. The pilot was identified as Jason Winters and the passengers were identified as Patricia Hicks, Sandra Williams, Lauren Hilty, Ross Mickel, Remy Mickel, Luke Ludwig, Rebecca Ludwig, Joanne Mera and Gabrielle Hanna.

Several witnesses told the NTSB the plane was spinning, rotating or spiraling during parts of the descent. One witness told the NTSB they did not hear any pitch change in the engine/propeller noise.

“The airplane was similar to a child with a toy airplane, dive bombing into a bathtub,” one witness said to the NTSB.

Fuselage view from front right

Nine witnesses near the accident site provided the NTSB with information about the accident. Four of the nine witnesses reported traveling to the accident site on a boat to assist. One pilot was flying nearby in a Cessna 120 and told the NTSB he encountered turbulence/windshear between 1,500 feet and 2000 feet above ground level.

“It was spinning and heading nose first towards the water,” one witness said.

The initial responders at the site included many private citizens, the U.S. Coast Guard, Island County Sheriff’s Office, Washington Department of Fish and Wildlife, Customs and Border Patrol and Tulalip Tribes. Private citizens recovered one floating victim and pieces of debris, which were turned over to the sheriff’s office. The USCG continued search operations for 24 hours after the accident. WDFW searched the area for evidence of the wreckage the day after the crash using onboard fish-finding sonar equipment. The search continued in Mutiny Bay near the last automatic dependent surveillance-broadcast location of the plane without results.

Sonar imaging from the search

On Sept. 7 the National Oceanic and Atmospheric Administration, Office of Coast Survey, Acting WA Navigation Manager reached out to the NTSB Western Pacific Regional Office to offer assistance. The group chair and the NOAA Navigation Response Team-Seattle deployed on Sept. 8 on a 34-foot-long aluminum survey boat, equipped with a multibeam sonar and side scan sonar. The team surveyed an area about 1.9 miles long by 0.75 miles wide. Searches continued as data began to narrow down potential locations for debris and victim recovery. Once the wreckage was discovered and identified, the groups began planning for recovery.

Due to the depth of the water, at approximately 190 feet, the most suitable tool for recovery was a work class remotely operated vehicle. The Deep Drone 8000 ROV, a controllable vehicle with scanning sonar and two arms designed by the Navy, was deployed in the recovery operation that began on Sept. 27. Parts of the plane were identified by the ROV and the main wreckage was rigged with a chain and connected to a crane hook on Sept. 29. The last two ROV dives on Sept. 30 expanded the search area and were concluded later that day. In total, there were 17 dives and 26 hours of bottom time. About 85 percent of the plane was recovered from the sea floor.

The NTSB identified a safety concern in October after investigators found the aircraft’s horizontal stabilizer actuator had separated into two pieces as a result of unthreading. An urgent safety recommendation was issued to the FAA and one to Transport Canada. During the examination of the airplane wreckage, the NTSB 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 examination also found that the circular wire lock ring, which is designed to prevent the clamp nut from unscrewing, was missing.

A missing or improperly installed horizontal stabilizer actuator lock ring is a critical safety hazard that can result in a reduction or loss of pitch control during flight. It is unknown whether the lock ring was in place before the crash and simply part of the 15 percent of the wreckage not recovered from the plane. The NTSB urged all operators of DHC-3 aircraft to conduct an immediate inspection and report findings to either the FAA or Transport Canada.

The docket contains hundreds of documents including reports on airplane performance, operations, structures, systems, maintenance records, laboratory examinations and witness statements. There are also materials like transcripts, videos and photos included. The public docket does not share any conclusion about how or why the crash occurred. A probable cause will be included in the final report, which the NTSB said would be issued at a later date and include analysis, findings, recommendations and probable cause determinations related to the accidents. Final reports can take 12-18 months to complete and are done to help prevent another similar tragedy from occurring.

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