'EASA aircraft' means an aircraft which is required by the Basic EASA Regulation and any implementing rules adopted by the Commission in accordance with that Regulation to hold an EASA certificate of airworthiness, an EASA restricted certificate of airworthiness or an EASA permit to fly;
Source Article 255 of the
Air Navigation Order
ORS4_4 doesn't exist, I think you mean
ORS4 No 804, which applies when
b) The aircraft is operated and maintained in accordance with, in the case of an EASA aircraft, the airworthiness provisions of Annex I to Regulation (EC) No. 2042/2003
or, in the case of a non-EASA aircraft, the airworthiness provisions of Part 3 of the Order applicable to private flight.
If the aircraft has a National Permit to Fly there is a separate exemption
ORS4 No 802 which does not contain the requirement since it's not applicable.