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

Controller
UNABLE Higher altitude
PROCEED DIRECT TO [position]
The ATC response in the following example is incorrect and shall never be used:
Pilot REQUEST CLIMB TO [level]
REQUEST DIRECT TO [position]
Controller UNABLE
PROCEED DIRECT TO [position]
4.5 Multi-element Uplink Messages
4.5.1 Combining multiple elements into a single message
Only uplink elements that are related to the overall message should be combined into a single
message.
Messages that contain unrelated elements could either cause confusion or result in the crew rejecting
the entire message when one of the elements on its own could have been acceptable. The following
multi-element uplink is an example of a clearance that can be unambiguously sent as a single
message.
WHEN READY
DESCEND TO AND MAINTAIN FL280
REPORT LEVEL FL280
When the elements are not dependent on each other, controllers should send a single element
clearance and wait for the response before sending a subsequent instruction.
4.5.2 Dependent Clearances
A dependent clearance is a message consisting of more than one clearance element, where the pilot
must comply with each of the elements. A rejection of any of the elements, either singly or in
combination, renders the entire clearance invalid. The following multi-element uplink is an example
of a dependent clearance:
CLIMB TO AND MAINTAIN FL330
AT FL330 PROCEED DIRECT TO TUNTO
REPORT LEVEL FL330.
In this example the aircraft must complete a change of level in order to be issued with an amended
route clearance.
Whenever possible, all elements of a dependent clearance should be sent in a single uplink message.
Sending the elements as individual messages may compromise safety or separation if the pilot accepts
Operation Manual of CPDLC V3.0 Algiers FIR 33