NOTE: Feedback indicates that this is the correct answer in the authority exam, although the callsign should actually be at the end of the message. It has been reported by students.

A conditional clearance is a clearance issued by an air traffic controller which does not become effective until a specified condition has been satisfied. Basically, once something has happened, then you can proceed with your action. For example:

• "After the departing aircraft; cross runway 28"
• "Behind the landing aircraft; line up runway 28 behind" NOTE: ‘behind' should be used twice.
• "After the Airbus 320 from left to right, taxi to holding point echo" etc.

Looking at the answer options:

“Behind the Airbus, Fastair56Y, line up and wait” --> INCORRECT. The word 'behind' is used twice in such a conditional clearance.

“Fastair56Y, behind the Airbus line up and wait, behind” --> CORRECT. This represents the correct phraseology, including the use of the word 'behind' twice.

“Fastair56Y, line up and wait, behind the Airbus” --> INCORRECT. The word 'behind' is used twice in such a conditional clearance.

“Behind the Airbus, line up and wait, Fastair56Y” --> INCORRECT. The word 'behind' is used twice in such a conditional clearance.

ICAO Doc 9432
2.8.3 Issue of clearance and read-back requirements

2.8.3.6 Other clearances or instructions, including conditional clearances, shall be read back or acknowledged in a manner to clearly indicate that they have been understood and will be complied with.