VATPAC Tutorial: Conditional Clearances
Below is an explanation of some common or uncommon ATC phrases that are often misunderstood. These are provided for both pilots (to help them understand what the controller means) and controllers (to improve their phraseology).
CONDITIONAL CLEARANCES (AIP GEN 3.4)
A conditional clearance is a procedure where an aircraft is instructed to do something, based on some other condition being met. The most common example is the instruction to "LINE UP BEHIND". AIP requires that the condition be stated at the beginning and then briefly reiterated at the end of the instruction. Note, the runway need only be identified where the possibility of confusion exists.
"QFA123, BEHIND THE ARRIVING A320, LINE UP AND WAIT [RUNWAY 34L] BEHIND."
Note the controller uses the word "behind" twice to promote understanding and compliance. The pilot would readback:
"BEHIND THE ARRIVING A320, LINE UP [RUNWAY 34L] AND WAIT, QFA123."
This means the pilot must identify the traffic referred to in the conditional clearance, wait for the arriving aircraft to pass, taxi onto the runway and await further instructions. If any doubt exists, the pilot shall hold position and confirm the clearance with ATC.