Section 21.187 - Issue of multiple airworthiness certification(a) An applicant for an airworthiness certificate in the restricted category, and in one or more other categories except primary category, is entitled to the certificate, if- (1) The applicant shows compliance with the requirements for each category, when the aircraft is in the configuration for that category;(2) The applicant shows that the aircraft can be converted from one category to another by removing or adding equipment by simple mechanical means;(3) The aircraft complies with the applicable requirements of part 34 of this subchapter; and(4) The airplane complies with the applicable requirements of part 38 of this subchapter.(b) The operator of an aircraft certificated under this section must have the aircraft inspected by the FAA, or by a certificated mechanic with an appropriate airframe rating, to determine airworthiness each time the aircraft is converted from the restricted category to another category for the carriage of passengers for compensation or hire, unless the FAA finds this unnecessary for safety in a particular case.(c) The aircraft complies with the applicable requirements of part 34.Doc. No. 5085, 29 FR 14569, Oct. 24, 1964, as amended by Amdt. 21-68, 55 FR 32860, Aug. 10, 1990; Amdt. 21-70, 57 FR 41369, Sept. 9, 1992