Manuel CPDLC V3.0. - Service d'Information Aéronautique Enna

the first uplink of a dependent clearance, complies with the instruction, and then responds UNABLE
to the next message when received. By the time that the controller has received the UNABLE
response, the aircraft could have begun executing the first instruction of a clearance that is invalid if
the pilot cannot comply with the second element.
The response to a multi-element uplink message will either be a WILCO or UNABLE that refers to
the entire message. It is not possible for the pilot to respond to individual elements of a multi-element
message.
NOTE: Care must be taken in the construction of dependent clearances to ensure that there is no
ambiguity present in the message. In the example above, the second element has been carefully
chosen to reinforce the requirement instead of using the word THEN followed by the route clearance
PROCEED DIRECT TO TUNTO.
The following message is an example of poor message construction as it does not unambiguously
convey to the pilot that the climb clearance must be completed prior to commencing the route
clearance component. This format SHOULD NOT be used for dependent clearances:
CLIMB TO AND MAINTAIN FL330
THEN
PROCEED DIRECT TO TUNTO
Operation Manual of CPDLC V3.0 Algiers FIR 34