The PIC of an aircraft to be operated in controlled airspace shall—
(a) ensure that an ATS flight plan is submitted and changes thereto are notified as prescribed in regulation 91.03.4;
(b) ensure that radio contact is established with the responsible ATSU and that radio communication is maintained as prescribed in regulation 91.06.16 except where such communication is accomplished using air data link; and
(c) for flight in controlled airspace, obtain and comply with air traffic control clearances and instructions: Provided that—
(i) the PIC of an aircraft may deviate from an air traffic control clearance in exceptional circumstances, but such deviation shall be reported to the responsible ATSU as soon as possible; and
(ii) the PIC of an aircraft may propose an amendment to an air traffic control clearance, but such amendment shall not be applied until acceded to by the responsible ATSU.