The following master's thesis was developed in collaboration with T.P.S. Group S.P.A.'s Airworthiness department. Based in Torino, this company specialises in the design and production of aeronautical parts and modifications. This work in particular focuses on the certification process of an external basket in both a short and a long version to be installed on an AS350 helicopter, with the objective of accommodating and transporting payload. Considering the maximum take-off weight of the subject aircraft, the project was carried out under Part 27 of the Federal Aviation Regulations with specific items being replaced with paragraphs from EASA's Certification Specifications 27 airworthiness standards and it encompasses virtually every area involved in a process of this kind.