Summary
The FAA proposes to adopt a new airworthiness directive (AD) for all Viking Air Limited Model DHC-7 airplanes. This proposed AD would require an inspection of certain SM-200 servo drive units (power servo motor and housing assemblies) for certain markings, related investigative action if necessary, and modification if necessary. This proposed AD results from a report that some SM-200 servo drive units that were not in configuration MOD H are installed on Model DHC-7 airplanes. MOD H prevents the internal clutch fasteners from backing out. We are proposing this AD to prevent the possibility of internal clutch fasteners from backing out, which could cause an inadvertent servo engagement and consequent reduced controllability of the airplane.