Use of paid parking space by other aircraft
8.  Where any fee has been paid in respect of an aircraft for the parking of the aircraft or the housing of the aircraft in a hangar on a monthly basis and the aircraft does not use the space evaded for it —
(a)another aircraft with the same taxi-weight may, with the written approval of the chief executive officer, use such space; and
(b)no rebate of the fee shall be granted under any circumstances.