Originally Posted by kraggy
do say Ryanair's ops team file a plan for a flight that would normally be scheduled and the CFMU issue a slot based on this request?
Yes, but slots are only issued if necessary - they aren't always. These flights are deemed to be "out of regulation" and can go any time providing the FPL is still live.
and if this slot is missed, will a new strip with updated dep time automatically come out of the atc system to the controllers for the conerned flight?
No - you miss your slot, you've missd your chance and you have to delay or refile the plan. Flight Plans within the IFPS zone (Europe basically) have to be delayed if the aircraft is going to be off blocks 15 minutes or more later. If you delay the plan then a new slot will be issued - might be 5 minutes later, might be 50, might even be out of regulation and no slot applicable.
What
DOESN'T work is crews knowing their slot, running late, and thinking "It's ok, ATC will let us go if we're outside slot tolerance" - we won't. It may be possible to get an extension if we have the time and opportunity to phone the Flow management people - but don't count on it.