The FAA has announced that all De Havilland Otter DHC-3 airplanes should remain grounded until all parts have been inspected. However, its latest statement does not mandate a grounding.
In the aftermath of last month’s Whidbey Island crash into Mutiny Bay that killed 10 people, the NTSB started an investigation, while urging U.S. Otter owners to keep their planes grounded until they can be inspected.
The new FAA airworthiness directive stated that an inspection must confirm that the stabilizer actuator lock ring is installed correctly by Dec 19.
The AD requires visual inspections of a stabilizer component to confirm a lock ring is present and correctly installed, and submitting the results to the FAA.
“Operators must perform the inspections within 10 hours of flight time after the AD takes effect,” the FAA said in a statement to GlobalAir.com. “The FAA began alerting U.S. DHC-3 operators last week about a Viking Air Limited service letter recommending the inspections. The missing ring could result in loss of control of the airplane. The investigation of a Sept. 4 fatal DHC-3 crash revealed the lock ring was missing. The AD affects approximately 63 U.S.-registered airplanes.”
Read the complete AD here.
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Following last month’s crash, the FAA issued an Emergency Airworthiness Directive (AD) for any owner of the De Havilland Otter DHC-3. The AD was issued on Oct. 4, exactly a month afterward. According to the FAA, this Emergency AD was prompted by multiple recent reports of cracks in the left-hand elevator auxiliary spar.
The AD called for an inspection to detect cracks, corrosion, and previous repairs. If not addressed, the aircraft could experience elevator flutter leading to elevator failure and possible loss of control of the airplane.
Recovered wreckage highlighted in green. Recovered flight controls highlighted in orange. (Source: NTSB)
After the investigation of the crash, the NTSB stated that investigators found the aircraft’s horizontal stabilizer actuator had separated into two pieces as a result of unthreading. The search recovered 85% of the airplane from the water and the wreckage was sent to Washington D.C. for further investigation by the NTSB Materials Laboratory.
This examination found that the actuator separated where the clamp nut threads into the barrel section. Furthermore, it was determined that the threads inside the barrel and the threads on the clamp nut separated by unthreading as opposed to being pulled apart in tension. A circular wire lock ring used to prevent the barrel and clamp nut from unthreading has not yet been located in the wreckage. According to the NTSB, this possible safety issue could result in a loss of airplane control.
Examples of horizontal stabilizer actuators and lock rings. On the left, the lock ring is fully inserted, and, on the right, the lock ring is partially inserted. (Source: NTSB)
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