SERA.8035 Communications

(a) An aircraft operated as a controlled flight shall maintain continuous air-ground voice communication watch on the appropriate communication channel of, and establish two-way communication as necessary with, the appropriate air traffic control unit, except as may be prescribed by the relevant ANSP in respect of aircraft forming part of aerodrome traffic at a controlled aerodrome.

(1)  The requirement for an aircraft to maintain an air-ground voice communication watch shall remain in effect when CPDLC has been established.

(b) The Secretary of State shall comply with the appropriate provisions on communication failures as have been adopted under the Chicago Convention. [...]