Airworthiness Directives; De Havilland Model DHC-8-100 and DHC-8- 300 Series Airplanes

This amendment revises an existing airworthiness directive (AD), applicable to certain De Havilland Model DHC-8-100 and DHC-8-300 series airplanes, that currently requires a revision to the Airplane Flight Manual (AFM) to advise flight crew members that certain cockpit indications may reveal faulty anti-collision strobe light units, and to provide procedures for subsequent flight crew and maintenance action. That AD also requires a modification that eliminates the need for the AFM revision. That AD was prompted by reports that the function of the proximity switch electronics unit (PSEU) may be adversely affected during operation of the white anti-collision lights. The actions specified by that AD are intended to ensure correct operation of the PSEU and its associated systems. This amendment revises the applicability of the existing AD to add one model of affected airplanes.