AD 2006-20-04 71 FR 56856

The FAA is adopting a new airworthiness directive (AD) for certain Bombardier Model DHC-8-102, -103, and -106 airplanes, and Model DHC-8-200 and DHC-8-300 series airplanes. This AD requires performing a one-time general visual inspection for non-conforming chain links of chain assemblies of the elevator trim system and gust lock system, and corrective actions if necessary. This AD also requires temporary revisions to the airplane flight manuals of the affected airplanes, which describe procedures for elevator trim checks. This AD results from reports of several failures of the elevator trim chain, due to hydrogen embrittlement. We are issuing this AD to prevent breakage of the elevator trim chain, which would prevent the actual position of the elevator trim tab from being annunciated to the flightcrew. Attempting to adjust the trim tab from the full nose up or full nose down position with a broken trim chain could result in misleading information relative to takeoff trim settings and consequent loss of control on takeoff.