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Scotts-Bell 47 throttle linkage concern prompts FAA actionScotts-Bell 47 throttle linkage concern prompts FAA action

The FAA has proposed to issue an airworthiness directive (AD) requiring inspections and adjustment of the throttle linkage of various models of the Scotts-Bell 47 helicopter to avoid loss of throttle control.

The Federal Aviation Administration is one of the many government agencies that have influence over general aviation. Photo by David Tulis.

The AD was prompted by several reports of throttle linkage separation from the engine carburetor shaft, which resulted in loss of throttle control, the FAA said. Its investigation determined that a “missing or improperly installed safety wire may fail to prevent an excessively worn splined carburetor shaft from separating from the throttle linkage.”

The investigation also found that “the unusual routing of the safety wire in this design along with a lack of clarity in the maintenance instructions may have contributed to nine other incidents.” Comments may be submitted on the AD, Docket No. FAA-2018-0440, until July 17.

The AD would require inspecting before further flight the throttle linkage connection at the engine carburetor for condition, security, and to determine if the safety wire is in place and captures the throttle linkage and the carburetor stop arm.

Before the first flight of each day, a visual check would be required of the throttle linkage to the carburetor attachment for installed safety wire, and for intact anti-sabotage lacquer. An owner/operator (pilot) may perform the visual check, and must document compliance as set forth in the AD.

The AD also would require adjusting, safety wiring, and applying anti-sabotage lacquer to the throttle linkage within 100 hours time-in-service or at the next annual or 100-hour inspection, whichever occurs first, and thereafter at each annual or 100-hour inspection, whichever occurs first. See the AD for procedures specific to models of the Scotts-Bell 47.

The FAA estimates that the AD would affect 698 helicopters. Cost estimates included the “minimal” cost of a pre-flight check of the throttle linkage connection by the pilot; a half-hour at an average labor rate of $85 to inspect the engine throttle linkage, for a cost of $43 per helicopter and $30,014 for the U.S. fleet; and adjusting and securing the throttle linkage, which would require about three work hours and $12 of parts, for a cost of $267 per helicopter, or $186,366 for the U.S. fleet, per occurrence.

Comments may be submitted online or by mail to U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590-0001.

Dan Namowitz

Dan Namowitz

Associate Editor Web
Associate Editor Web Dan Namowitz has been writing for AOPA in a variety of capacities since 1991. He has been a flight instructor since 1990 and is a 30-year AOPA member.
Topics: Aircraft Regulation, Airworthiness Directives, Maintenance

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