Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Short Brothers Model SD3-60 SHERPA, SD3-SHERPA, SD3-30, and SD3-60 series airplanes. This proposal would require replacement of the existing pneumatic de-icing boot pressure indicator switch with a newly designed switch. This proposal is prompted by an occurrence on a similar airplane model in which the pneumatic de-icing boot indication light may have provided the flightcrew with misleading information as to the proper functioning of the de-icing boots. The actions specified by the proposed AD are intended to prevent ice accumulation on the airplane leading edges, which could reduce controllability of the airplane.