This Master Thesis has been developed within the Leonardo S.p.a. - Helicopters Division - Airworthiness Office - located in Cascina Costa di Samarate, Varese, Italy. The work presented through this Thesis has been part of an Internship carried out at the Company Facilities. In the dynamic aviation industry, the ability to modify and update aircraft designs while ensuring safety and regulatory compliance is of paramount importance. The aim of this thesis is to analyze the company background of the work of managing the design, development and certification processes associated with changes to an aircraft type certificate. This research delves into the intricate procedures and issues that arise when seeking to modify or enhance an aircraft’s type certificate.