4.2.3.3.1 When basic flight plan data for a flight has been provided, an EST message shall be transmitted by each area control centre or flight information centre to the next area control centre or flight information centre along the route of flight.
4.2.3.3.2 An EST message shall be transmitted in sufficient time to permit the air traffic services unit concerned to receive the information at least 20 minutes before the time at which the aircraft is estimated to pass the transfer of control point or boundary point at which it comes under the control of such unit, unless another period of time has been prescribed by the appropriate ATS authority. This procedure shall apply whether or not the area control centre or flight information centre responsible for origination of the message has assumed control of, or established contact with, the aircraft by the time the transmission is to be effected.
4.2.3.3.3 When an EST message is transmitted to a centre which is not using automatic data processing equipment, the period of time specified in 4.2.3.3.2 may be insufficient, in which case an increased lead-time shall be agreed.
4.2.3.4 Co-ordination (CDN) messages
4.2.3.4.1 A CDN message shall be transmitted during the co-ordination process by an accepting unit to the transfer-
IX. Air Traffic Services Messages
ring unit when the former wishes to propose a change to co-ordination data as contained in a previously received CPL or EST message.
4.2.3.4.2 If the transferring unit wishes to propose a change to the data contained in a CDN message received from the accepting unit, a CDN message shall be transmitted to the accepting unit.
4.2.3.4.3 The process described above is repeated until the co-ordination process is completed by the transmission of an acceptance (ACP) message by one of the two units concerned. Normally, however, when a change is proposed to a CDN message, direct-speech circuits shall be used to resolve this issue.
4.2.3.4.4 After the co-ordination process has been completed, if one of the two ATS units concerned wishes to propose or notify any change in basic flight plan data or conditions of transfer, a CDN message shall be transmitted to the other unit. This requires that the co-ordination process must be repeated.
4.2.3.4.5 A repeated co-ordination process requires to be completed by the transmission of an ACP message. Normally, in a repeated co-ordination process, direct-speech circuits shall be used.
4.2.3.5 Acceptance (ACP) message
4.2.3.5.1 Unless special arrangements have been made between the air traffic control units concerned in accordance with Part VIII, 4.2.5, an ACP message shall be transmitted by an accepting unit to the transferring unit to indicate that data in a CPL or an EST message is accepted. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址:Rules of the Air and Air Traffic Services(105)