39.—(1) Subject to paragraph (3), a national certificate of airworthiness issued for a non-EASA aircraft registered in the United Kingdom ceases to be in force if—
(a)the aircraft or any part of the aircraft or such of its equipment as is necessary for the airworthiness of the aircraft has been overhauled, repaired, replaced, modified or maintained;
(b)maintenance or an inspection of the aircraft or of any equipment necessary for the airworthiness of the aircraft is required by a maintenance programme established under article 54;
(c)maintenance of the aircraft or of any equipment necessary for the airworthiness of the aircraft has been made mandatory by a directive issued by the CAA;
(d)an inspection for the purpose of ascertaining whether the aircraft remains airworthy has been made mandatory by a directive issued by the CAA; or
(e)any modification of the aircraft or of any equipment which is necessary for the airworthiness of the aircraft, has been made mandatory by a directive issued by the CAA for the purpose of ensuring that the aircraft remains airworthy.
(2) A certificate of airworthiness which has ceased to be in force under paragraph (1) becomes valid again on the issue of a certificate of release to service under this Order or in accordance with paragraph 21A.163(d) of Part 21 relating to the overhaul, repair, replacement, modification, maintenance or inspection.
(3) A certificate of airworthiness which would not be in force by reason of paragraph (1) remains in force if the aircraft is flying in the circumstances specified in article 44(3).