10.1.2 Coordination between ATC units providing air traffic service within contiguous control areas. ATC units shall forward from unit to unit, as the flight progresses, necessary flight plan of information. When so required by agreement between the appropriate authorities to assist in the separation sitcraft, flight and flight progress information for along routes in flight to night region boundaries shall also be provided to routes or in charge of the the ATc units information regions adjacent such routes Nor 1- sch route or portion of route is often referred to as an area common interest, the extent of which is a usually determunedby Dhe requured separation mlnima Note 2 See also 1024 0.1212 The flight plan and control information shall be transmitted in sufficient time to permit reception and coordination between the units con analysis of the data by the receiving and Note See Chapter 11 and Appendices 3 and 6 for details regardung messages their contentandtime of transmission. 10.1.2 2 TRANSFER OF CONTROL 10 221 The responsibility for the control ofan aircraft be transferred from the ATC unit to the unit at next e time of crossing the common control area boundary as determined by the unit having control of the aircraft or at such other point or time as has been agreed between the two units. 01222 Where specified in letters of agreement between the units concerned, and when transferring an aircraft, the transferring unitshallnotify the that the is in position to transferred, and specify that the responsibility for control should be assumed by the accepting unit forthwith at the time of crossing the control boundary or other transfer coatrol point in f agreement between the ATC or at such other point or time coordinated between the two units. 101223 If the transfer of control time or point is other than forthwith, the accepting ATC unit shall not alter the clearance of the aircraft prior to the agreed transfer of control time or point without the approval of the transferring unit 10.1.224 If transfer of communication is used to transfer an aircraft to a receiving ATC unit, responsibility for control shall not be assumed until the time of crossing the control area boundary or other transfer of control point specified in letters of agreement between the ATC units 10.1.225 When transfer of control of identified aircraft is to be effected, the appropriate procedures specified in chapter 8 section g 74, shall be applied.