Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Dornier Model 328-100 and -300 series airplanes. This proposal would require inspection of the metal oxide varistor (MOV) modules and transient absorption zener (TAZ) diodes to determine if those parts are outside of tolerance limits, and replacement of MOV modules and TAZ diodes with new parts, if necessary. This action is necessary to prevent the failure of critical ice protection systems following a lightning strike, which could result in reduced controllability and degraded performance of the airplane in the event of an encounter with icing conditions. This action is intended to address the identified unsafe condition.