DEFINITION:

It comprises all the activities related with obtaining the airworthiness certification issued for any kind of aircraft by the national aviation authority in the state in which the aircraft is registered.

Following FAA regulations there are two general types of airworthiness certifications:

• Standard airworthiness certificate for: Normal, Utility, Acrobatic, Commuter, Transport, Manned free balloons and Special classes.
• Special airworthiness certificate including many special classes like personal use, agricultural, patrolling, weather control and experimental aircrafts (including unmanned aircraft systems)

(Source: FAA regulations: https://www.faa.gov/aircraft/air_cert/airworthiness_certification/aw_overview/  and PAE own elaboration)