The Federal Aviation Administration (FAA) has issued an emergency Airworthiness Directive (AD) for Viking Limited DHC-3 Otter airplanes to address possible issues with the lock ring on the stabilizer.
The emergency AD is the second such directive to be issued by the agency amid an investigation into the crash of the de Havilland Otter turboprop that occurred in September near Seattle killing all 10 persons on board. The AD is effective immediately.
Per a statement from the FAA, 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.
Last week, the FAA began alerting U.S. DHC-3 operators about a Viking Air Limited service letter recommending the inspections.
The AD affects approximately 63 U.S.-registered airplanes.
The accident airplane was registered to Northwest Seaplanes, a Part 135 operation. At the time of the accident, the airplane was en route from Friday Harbor Seaplane Base (W33) to Renton Municipal Airport (KRNT). According to witnesses, the aircraft was flying at an altitude of approximately 600 feet over Mutiny Bay when it suddenly pitched down and hit the water.
How We Got here
On October 24, the National Transportation Safety Board (NTSB) issued a factual report on the accident noting that the lock ring on the stabilizer was missing. Although the report stopped short of identifying the missing part as the cause of the September 4 crash, the report did note that without the lock ring, the horizontal stabilizer, which controls the aircraft’s pitch, can experience an uncommanded drop, putting the aircraft into an irrecoverable dive.
The NTSB, the FAA, and Air Transport Canada worked together to identify potential issues with the aircraft that might have contributed to the accident, and many seaplane operators took it upon themselves to perform extra inspections of their fleets out of an abundance of caution. No other issues were reported.
It took more than a week for the NTSB, along with the help of the U.S. Navy and sophisticated sonar equipment, to locate the wreckage, as the aircraft disintegrated upon entering the water.
The depth and strong currents made it difficult to retrieve the wreckage. The NTSB notes approximately 85 percent of the aircraft was pulled from the water.
The remains of seven of the 10 persons on board have been recovered.