It is not uncommon for a banner tow operator to configure aircraft for banner towing operations  in a manner and to such an extent that the aircraft no longer meets the requirements of § 21.187.  After proper application, these aircraft can be issued a Special Airworthiness Certificate in the  restricted category, and limited to banner towing operations only.  Aircraft that are modified and certificated under § 21.25 for special purpose operations will be  issued operating limitations with the CoW. The operating limitations specify the type and scope  of operations for which the aircraft may be used, and the aircraft must be operated as prescribed  in § 91.313.  No person may operate a civil aircraft unless an appropriate airworthiness certificate and  effective U.S. Registration Certificate are displayed in the aircraft at the cabin or cockpit  entrance, so that it is legible to the passengers or crew as prescribed in § 91.203(b).  The current edition of AC 20-65, U.S. Airworthiness Certificates and Authorizations for  Operation of Domestic and Foreign Aircraft, provides guidance and general information  regarding the issuance of airworthiness certificates for U.S.-registered aircraft.  Aircraft with a Special Airworthiness Certificate in the restricted category issued under § 21.25  are subject to the same maintenance and record keeping requirement as aircraft operated with a  standard airworthiness certificate, part 43, § 43.1(a)(1).  All maintenance, repairs, and alterations must be operationally checked, approved, and  documented as prescribed by § 91.407.  All major repairs and alterations to the aircraft and appliances as defined in 14 CFR part 1 may  be returned to service as long as the person approving the return to service is a person specified  in § 43.7 or § 43.17, and the approval for the return to service of the aircraft conforms to all  regulatory requirements as prescribed in part 43 appendix B.  Title 14 CFR part 65, § 65.95(a)(1) states that the holder of an inspection authorization may  return an aircraft to service after major repair or major alteration if the work was done in  accordance with technical data approved by the Administrator. The owner or operator as  prescribed in § 91.417(a), (b), and (c) must maintain these records.  Aircraft that are used for a special purpose like banner towing must be inspected annually as  required by § 91.409.  Banner tow aircraft that are operated with a Special Airworthiness Certificate in the restricted  category under § 21.25 must also be marked in accordance with § 45.23(a) and (b). Aircraft  operated in the restricted category must display the word “RESTRICTED” near each entrance to  the cabin or cockpit on that aircraft, in letters not less than 2 inches or more than 6 inches in  height.  Maintenance Requirements.  UNCONTROLLED COPY WHEN DOWNLOADED  Check with FSIMS to verify current version before using  6-3 (and 6-4) 