GM1 SERA.8015(f)(4) Air traffic control clearances
CAA ORS9 Decision No. 1
COORDINATION OF CLEARANCES — DOWNSTREAM CLEARANCE
(a) In such cases it is assumed that contact of a downstream ATC unit is initiated by the pilot. Therefore, the rules require that the aircraft maintain the necessary two-way communication with the current ATC unit.
(b) In cases where an aircraft cannot maintain two-way communication whilst obtaining a downstream clearance, the pilot needs to seek the acceptance to leave momentarily the communication channel of the current ATC unit prior to contacting a downstream ATC unit.