Experimental Airworthiness Certificates
http://www.faa-aircraft-certificatio...ification.html
https://www.caa.co.uk/Commercial-ind...ermits-to-Fly/
Commission Regulation (EU) 748/2012 Subpart P allows for the issue of a Permit to Fly to an Part 21 aircraft when the Certificate of Airworthiness (CAA Form 25) or Restricted C of A (CAA Form 24) is temporarily invalid or when an aircraft is unable to comply with the regulations set for the issue of a C of A but is still capable of safe flight under defined conditions.