Airworthiness Directives; Bombardier, Inc. Airplanes

We are superseding airworthiness directive (AD) 2011-13-08 for certain Bombardier, Inc. Model DHC-8-400 series airplanes. AD 2011-13- 08 required a free-play check for excessive free-play of the shaft swaged bearing installed in the tailstock end of each elevator power control unit (PCU), and replacing any PCU on which the bearing exceeds allowable limits with a serviceable PCU. This new AD adds airplanes to the applicability from that of AD 2011-13-08. This AD was prompted by a determination that additional airplanes are affected by the identified unsafe condition. We are issuing this AD to detect and correct excessive free-play of the swaged bearings, which could lead to excessive airframe vibrations and difficulties in pitch control, and consequent loss of controllability of the airplane.