If you were given the conditional instruction "After the landing/departing aircraft line up and wait"
Do you still wait for the aircraft to leave the runway before lining up?
For example if you were at a field with a runway say 1600m long and the landing aircraft missed the first taxi way off the runway, would you wait for him to call vacated before lining up or once he has passed you would you be expected to line up and wait for take off clearance?
Do that to me at certain times of the day and you are likely to have your line up clearance cancelled followed by a
VERY long wait.
Conditional clearances are used to speed things up - i.e, you know someone is about to call you, so get another transmission / instruction out of the way in the free air time you have.
Now - if I've got two inbounds, with a gap in between to depart you - you'll get the conditional clearance that you describe. Any delay waiting for the first aircraft to vacate means you could baulk the second inbound - so as soon as it's passed you, get your backside on the runway and be ready.
After all - what are you worried about? The last time I looked there weren't that many aircraft fitted with reverse gear - the guy on the runway isn't going to back into you is he?
