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, and SD3-30 series airplanes. This proposal would require replacement of existing oxygen system ``O'' rings with improved wear-resistant ``O'' rings. 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 the loss of oxygen from the aircraft oxygen system, which could result in an insufficient supply of oxygen being provided to the airplane flight crew and passengers in the event of an emergency.