The topic of the thesis is framed within the activities of a project whose purpose is to convert a civil platform into a multi-role aircraft capable of long range maritime patrol mission, as well as anti-submarine and anti-surface warfare mission. Design and modification activity will be done side by side with the military type certification process, based on both civil and military regulations: FAA Title 14 CFR (Part 21, 25 etc.) and military standards (MIL-STDs and MIL-HDBKs) where FAA cannot be applicable. Within this contest the main objective is to analyze the verification and certification process following the major modification, in order to identify all the critical issues and to propose some design solutions.