The following thesis was written within Leonardo S.p.A - Helicopter Division in Cascina Costa, Samarate (VA), Italy. It delineates the basic principles behind the internal procedures implemented by a generic European Design Organization within the aviation sector under the latest amendment of the Commission Regulation (EU) No 748/2012 - Annex I (Part 21) and actively engaged in the helicopter market. Each procedure described should be understood as not specifically attributable to Leonardo S.p.A - Helicopter Division, but intended as the outcome of what the competent Authority requires from a DO located in the EU, in order to show compliance with the current Airworthiness standards and Environmental Protection requirements.