14 CFR 21.175: Airworthiness certificates: classification.

(a) Standard airworthiness certificates are airworthiness certificates issued for aircraft type certificated:

(1) In the normal, utility, acrobatic, commuter, or transport category;

(2) As manned free balloons; or

(3) As special classes of aircraft.

(b) Special airworthiness certificates are airworthiness certificates issued for:

(1) Aircraft type-certificated in the primary, restricted, provisional, or limited category;

(2) Aircraft certificated in the light-sport category;

(3) Aircraft operating for an experimental purpose; or

(4) Aircraft operating under a special flight permit.