Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Bombardier Model DHC-8-102, -103, and -106 airplanes, and DHC-8-200 and DHC-8-300 series airplanes. This proposed AD would require performing a one-time inspection for non-conforming chain links of chain assemblies of the elevator trim system and gust lock system, and corrective actions if necessary. This proposed AD would also require temporary revisions to the airplane flight manuals of the affected airplanes, which describe procedures for elevator trim checks. This proposed AD results from several reports of failure of the elevator trim chain, due to hydrogen embrittlement. We are proposing 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 to the full nose up or full nose down position with a broken trim chain could cause reduced control during airplane rotation on the ground or a stall during flight.