Summary
We propose to adopt a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400 series airplanes. This proposed AD was prompted by reports of inadvertent deployment of a single outboard spoiler during flight. This proposed AD would require replacement of the power control units (PCUs) for the outboard spoilers with upgraded PCUs. We are proposing this AD to prevent leakage of the piston head seal and piston rod seals of the outboard spoiler PCUs, which could result in inadvertent spoiler deployment and reduced controllability of the airplane.