Federal Aviation Administration order points to one possible cause of Whidbey seaplane crash
National Transportation Safety Board investigators look at the recovered engine of the DHC-3 Otter that crashed on September 4 off Whidbey Island.
The Federal Aviation Administration has issued a warning regarding potential weaknesses in parts of the tail of Otter seaplanes, the same type of aircraft that crashed off Whidbey Island last month.
The emergency airworthiness directive, issued Tuesday, warns of potential cracks and corrosion in the movable surface of the horizontal tail that controls the plane’s pitch. The directive is not a result of the investigation into the fatal crash in Mutiny Bay, which killed 10 people, but does suggest one possible cause.
The directive warns that, if not addressed, the cracks and corrosion could lead to a structural failure in the tail and “loss of control of the airplane.”
A person close to the Mutiny Bay crash investigation said the directive was spurred when mechanics discovered a crack in the tail of another Otter during a routine inspection unrelated to the deadly crash.
The person spoke anonymously because they were not authorized to release information about the ongoing National Transportation Safety Board investigation.
The directive states that the FAA received “multiple recent reports” of cracks in the same part: the elevator, a movable surface at the rear of the horizontal tail.
The Federal Aviation Administration has issued a warning regarding potential weaknesses in parts of the tail of Otter seaplanes, the same type of aircraft that crashed off Whidbey Island last month.
The emergency airworthiness directive, issued Tuesday, warns of potential cracks and corrosion in the movable surface of the horizontal tail that controls the plane’s pitch. The directive is not a result of the investigation into the fatal crash in Mutiny Bay, which killed 10 people, but does suggest one possible cause.
The directive warns that, if not addressed, the cracks and corrosion could lead to a structural failure in the tail and “loss of control of the airplane.”
A person close to the Mutiny Bay crash investigation said the directive was spurred when mechanics discovered a crack in the tail of another Otter during a routine inspection unrelated to the deadly crash.
The person spoke anonymously because they were not authorized to release information about the ongoing National Transportation Safety Board investigation.
The directive states that the FAA received “multiple recent reports” of cracks in the same part: the elevator, a movable surface at the rear of the horizontal tail.
In addition, there have been a series of other nonfatal Otter incidents involving elevator failure.
A sudden elevator failure can cause a plane to pitch immediately nose-down, similar to the trajectory reported by some witnesses of the September 4 crash, said Douglas Wilson, a Seattle-based seaplane pilot and president of aviation consulting firm FBO Partners.
The Mutiny Bay crash plane was a de Havilland Canada DHC-3 Otter turboprop operated by Renton-based Friday Harbor Seaplanes.
Todd Banks, president of Kenmore Air, which flies similar Otter seaplanes, said investigators could be examining as many as a dozen possibilities, ranging from structural failures of the airframe to a pilot health emergency.
However, he said the timing of the FAA directive is “interesting” and that something going wrong with the control surface on the tail is likely one focus of the investigation.
NTSB spokesperson Peter Knudson said via email Friday that in the Mutiny Bay crash investigation “the wreckage examination and records review are still underway.”
“We will be looking at all the structure and systems on the airplane to determine if there were any malfunctions or failures that contributed to the accident,” he said.
An FAA spokesperson said Friday “the investigation is ongoing. No cause has been determined.”
Multiple recent reports of cracks
Tuesday’s FAA directive states that it was “prompted by multiple recent reports of cracks in the left-hand elevator auxiliary spar.”
Delivered weeknights, this email newsletter gives you a quick recap of the day's top stories and need-to-know news, as well as intriguing photos and topics to spark conversation as you wind down from your day.
This unsafe condition, if not addressed, could lead to “elevator failure, with consequent loss of control of the airplane,” the directive states.
The auxiliary spar is the trailing edge of the elevator, which flaps up or down to move the nose of the plane up or down.
The left elevator is interconnected with and moves in sync with the flaps on the wings to enhance stability.
The last DHC-3 Otters were built in the late 1960s. Today’s fleet of aging workhorse seaplanes has been modified and rebuilt over the years. They need constant maintenance to fight the corrosive effects of seawater.
The FAA directive mandates “repetitive detailed visual inspections of the entire left-hand elevator auxiliary spar for cracks, corrosion, and previous repairs, and depending on the findings, replacement of the left-hand elevator auxiliary spar.”
The wording requires urgent action, indicating the danger is considered serious.
Within three days of receipt of the directive all Otter operators are instructed to “remove the left-hand elevator tab from the elevator and perform a detailed visual inspection.”
Results of the inspections have to be reported back to the FAA within 10 days.
Wilson of FBO Partners said daily visual inspection of the elevator is not easy on a seaplane.
That’s because when a seaplane is docked, with one of its floats tight against the dock, the tail is at a height and a distance from the dock that makes a thorough visual inspection difficult. The only way to do so is to pull the plane out of the water and do a complete inspection on dry land, Wilson said.
Following a 1995 DHC-3 Otter in-flight vibration incident in Ketchikan, Alaska, caused by cracks in an elevator tab, the operator’s director of maintenance told NTSB investigators that “the airplane’s tail is approximately 10 to 11 feet above the ground and is very difficult to examine during pre-flight.”
Past elevator failure incidents
The FAA did not detail where any of the recent multiple reports of cracks in Otter elevator spars occurred.
In-depth journalism takes time and effort to produce, and it depends on paying subscribers. If you value these kinds of stories, consider subscribing.
However, several past accident reports show elevator failure as a cause.
In May, a DHC-3 Otter crashed nose down into forested terrain while coming in to land in Yakutat, Alaska. The pilot had noticed the elevator not responding fully to his controls at various points in the flight and the airplane pitching up alarmingly.
No one died but the pilot and three passengers on board suffered serious injuries. The NTSB said that accident is still under investigation.
In 2014, an Otter experienced “an anomalous in-flight vibration and uncommanded nose down pitch during cruise flight in the vicinity of Homer, Alaska,” an NTSB report states.
No one was injured. But the airplane’s right elevator “sustained substantial damage.”
In 2015, another Otter in cruise flight near Skwentna, Alaska, also experienced unusual vibration. After landing, the tab on the right-hand elevator, which had been poorly repaired, was found to be damaged.
With investigators not yet finished examining the wreckage from the Mutiny Bay crash, it’s impossible to definitively point to the cause. For sure, they will be looking for evidence of elevator failure as a serious focus of the inquiry.
This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed.
Investigator In Charge (IIC): Brazy, Douglass
The National Transportation Safety Board travelled to the scene of this accident.
Additional Participating Entities:
Matt Rigsby; Accident Investigation and Prevention (AVP); Washington, District of Columbia
Federal Aviation Administration / Flight Standards District Office; Seattle, Washington
Northwest Seaplanes Inc
Friday Harbor Seaplane Tours
Location: Freeland, Washington
Accident Number: DCA22MA193
Date and Time: September 4, 2022, 15:09 Local
Registration: N725TH
Aircraft: DEHAVILLAND DHC-3
Injuries: 10 Fatal
Flight Conducted Under: Part 135: Air taxi & commuter - Scheduled
On September 4, 2022, at 1509 Pacific daylight time, a de Havilland DHC-3, N725TH, was substantially damaged when it impacted Mutiny Bay near Freeland, Washington, and sank. The pilot and 9 passengers were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 135 scheduled flight. The US Coast Guard and good Samaritans responded to the accident site.
The accident occurred during the pilot’s second trip of the day; each trip involved multiple flight legs. A review of Federal Aviation Administration (FAA) tracking data revealed that the accident flight departed from Friday Harbor Seaplane Base (W33), Friday Harbor, Washington, about 1450 with a destination of Renton Municipal Airport (RNT), Renton, Washington. The track data indicated the airplane flew a southerly heading before turning south-southeast. The en route altitude was between 650 and 975 ft above mean sea level (msl), and the groundspeed was between 115 and 125 knots. At 1508:43 the altitude increased to 1,125 ft, and the groundspeed reduced to 109 knots. At 1508:49, the altitude decreased to 875 ft and the groundspeed reduced to 100 knots. The tracking data ended at 1508:51, at an altitude of 700 ft and groundspeed of 55 knots.
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, near-vertical descent until it impacted water in Mutiny Bay. Several witnesses described the airplane as “spinning,” “rotating,” or “spiraling” during portions of the steep descent. One witness reported hearing the engine/propeller noise and noted that he did not hear any “pitch change” in the noise.
The pilot began working for the operator in 2013 and was one of two pilots who flew the DHC3, which he began flying in 2017. He had accrued a total of 4,686 flight hours as of May 31, 2022. His total flight hours in the DHC-3 have not yet been determined. He received training in emergency drills and procedures in May 2022, and an aircraft competency check in June 2021.
The airplane’s most recent 100-hour inspection was performed on September 1, 2022. Included at that time were recurring inspections required by Airworthiness Directives (AD) 83-04-05 (control column lower assembly) and 2011-18-11 (elevator control tabs). A left-hand rudder retract cable was replaced during the 100-hour inspection. The previous 100-hr inspection was performed on August 16, 2022, which also included the recurring AD inspections noted above. At that time, the horizontal stabilizer hinge bolts, a right-hand engine ignitor, and a left-hand float locker latch were replaced.
The airplane was not equipped nor was it required to be equipped with a flight data recorder or cockpit voice recorder. A King 560 Enhanced Ground Proximity Warning System was installed, which can retain some parametric flight data; however, the unit was not crash-protected. Some floating debris was recovered by local authorities and good Samaritans who responded to the accident site. This included three 6-ft sections of aluminum honeycomb panels used for flooring in the airplane, a seat cushion and seat belt, and small sections of foam, consistent with a modification made to the landing floats.
The NTSB structure’s group chairman went on board vessels provided by the Washington Department of Fish and Wildlife, the National Oceanic and Atmospheric Administration (NOAA) and the University of Washington to collect data using varying types of sonar equipment.
A sonar survey of the accident area located the main wreckage and debris field at a depth of about 190 ft.
At 1515, the automated weather observing station at Jefferson County International Airport (0S9), located 10 nautical miles northwest of the accident site, reported wind from 310° at 10 knots, visibility 10 statute miles, few clouds at 4,000 ft and 7,500 ft, broken clouds at 9,000 ft, temperature 20°C, dew point 14°C, and an altimeter setting of 30.02 inches of mercury.
Additionally, pilots flying in the vicinity of the accident area reported turbulence and a scattered cloud layer at 2,300 ft.
The US Navy will be assisting the NTSB with the wreckage recovery, and examination will begin once the wreckage is recovered.
Douglass Brazy, Investigator In Charge, onboard NOAA S3006 survey boat.
Aircraft and Owner/Operator Information
Aircraft Make: DEHAVILLAND
Registration: N725TH
Model/Series: DHC-3
Aircraft Category: Airplane
Amateur Built:
Operator:
Operating Certificate(s) Held: Commuter air carrier (135)
Operator Designator Code:
Meteorological Information and Flight Plan
Conditions at Accident Site: VMC
Condition of Light: Day
Observation Facility, Elevation: K0S9
Observation Time: 15:15 Local
Distance from Accident Site: 10 Nautical Miles
Temperature/Dew Point: 20°C /14°C
Lowest Cloud Condition: Few / 4000 ft AGL
Wind Speed/Gusts, Direction: 10 knots / , 310°
Lowest Ceiling: Broken / 9000 ft AGL
Visibility: 10 miles
Altimeter Setting: 30.02 inches Hg
Type of Flight Plan Filed: Company VFR
Departure Point: Friday Harbor, WA (W33)
Destination: Renton, WA (RNT)
Wreckage and Impact Information
Crew Injuries: 1 Fatal
Aircraft Damage: Substantial
Passenger Injuries: 9 Fatal
Aircraft Fire: Unknown
Ground Injuries: N/A
Aircraft Explosion: Unknown
Total Injuries: 10 Fatal
Latitude, Longitude: 47.99032,-122.58502
Those who may have information that might be relevant to the National Transportation Safety Board (NTSB) investigation may contact them by email witness@ntsb.gov, and any friends and family who want to contact investigators about the accident should email assistance@ntsb.gov. You can also call the NTSB Response Operations Center at 844-373-9922 or 202-314-6290.