Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Bombardier Model DHC-8-100 series airplanes. This proposal would require changing the power supply for the thunderstorm lights from the left secondary bus to the left essential bus. This proposal is prompted by issuance of mandatory continuing airworthiness information by a foreign civil airworthiness authority. The actions specified by the proposed AD are intended to prevent a failure of the thunderstorm lights in the cockpit after loss of all generated electrical power. This condition could result in the cockpit instruments not being visible to the flight crew during certain emergency procedures, and consequent reduced controllability of the airplane.