Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all de Havilland Model DHC-7 series airplanes. This proposal would require performing a review of the airplane maintenance records to determine if any insulation blankets have been repaired or changed during service, and various follow- on actions, if necessary. This proposal is prompted by reports of corrosion forming on areas of the airplane structure where black film thermal insulation blankets are used. The actions specified by the proposed AD are intended to prevent such corrosion, which could result in degradation of the structural capability of the airplane fuselage and consequent sudden loss of cabin pressure.