For an aircraft or its part to be certified, it must usually have been designed and manufactured by approved organisations. The party responsible for the design of an aircraft or its part is the Type Certificate Holder’s design organisation (DOA) and for possible changes and repairs, the design organisation that has approved their design. The European Aviation Safety Agency EASA issues the approvals of the Design Organisations and oversees their operation. The Design Approval Holder has the right and obligation to produce the required maintenance and manufacturing instructions and keep them up to date for as long as the product is used.
The holder of the DOA (Design Organisation Approval) has the right to design and classify modifications in accordance with its design manual, taking into account the applicable airworthiness requirements (Certification Specifications). The POA (Production Organisation Approval) entitles the organisation to manufacture products (aeroplanes, engines and propellers) and parts as well as appliances for aviation equipment according to the approved instructions.