 There are a number of other methods of compliance, including parts manufactured to government or industry standards, parts manufactured under technical standard order authorization [TSO], owner-/operator-produced parts, experimental aircraft, field approvals, etc.PMA-holding manufacturers are permitted to make replacement parts for aircraft, even though they are not the original manufacturer of the aircraft.The process is analogous to 'after-market' parts for automobiles, except that the United States aircraft parts production market remains tightly regulated by the FAA.