Here is a quick summary regarding maintenance:
Certificated airplanes must be maintained in accordance with their type certificate. Modifications must be FAA-approved by Field Approval or STC. All maintenance must be performed under supervision of A&P; Annual by IA. Certificated airplanes are subject to ADs with mandatory compliance. Certificated airplanes must be repaired and maintained with FAA-approved parts.
Certificated airplanes must be operated in accordance with factory-provided POH. These planes have standard airworthiness certificates.
Experimental amateur built (E-AB) airplanes do not have type certificates and thus do not require field approvals or STCs to be modified. Major modifications as described in the Operating Limitations of each plane must be tested in an approved flight test area for an amount of time determined by the local FSDO (usually 5 hours). These modifications may be performed by anyone. The flight testing may be performed by anyone holding an appropriate pilot certificate (usually PPL).
Maintenance of E-AB airplanes may be performed by anyone. A yearly condition inspection must be performed by someone with a Repairman’s Certificate for that airplane (typically the original builder), or it may be performed by a licensed A&P (no IA required). E-AB airplanes may be maintained with any other parts, subject only to the eventual approval of the person signing the yearly condition inspection.
The FAA does not issue ADs on E-AB airplanes, thus none apply. The applicability of ADs to certificated parts in E-AB airplanes is unclear. Some local FSDOs demand AD compliance on items such as engines and props, but the authority to do so is in doubt. The EAA is currently seeking clarification of this point from the FAA.
E-AB airplanes have Special Airworthiness Certificates and must be operated in accordance with their Operating Limitations, which are issued for each E-AB airplane individually.