Airworthiness Directives; Bombardier, Inc. Airplanes

We are superseding an existing airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400 series airplanes. That AD currently requires a modification to trim the edge of the bumper plate, including performing an inspection for damage or cracks of the bumper plate and base fitting, and replacing any damaged or cracked part. That AD also currently requires, for certain airplanes, reidentifying the bumper plate. This new AD requires, for airplanes on which the reidentification is done, an operational check of the alternate extension system of the main landing gear (MLG), and repair if necessary. This AD was prompted by the determination that an operational check must be done after reidentifying the bumper plate to ensure the identified unsafe condition is addressed. We are issuing this AD to detect and correct failure of the MLG to extend and lock, which could adversely affect the safe landing of the airplane.