pprune radar
You are correct of course. I was perhaps a bit flippant with my “launching them off” statement.
This is going somewhat off topic, especially as it's in the private flying forum and it's not often that GA get caught up in slots although it has happened to me once!
I can't say what goes on in the various towers regarding agreements with CFMU or flow control.
It seems to me that the ground controller has to make a decision on when to give start up clearance and once the aircraft is in the queue at the hold it's surely sensible to let the aircraft depart if it's only a couple of minutes adrift of it's CTOT margin. I realise that the commander shares this responsibility, however the commander does not know what sort of delays to expect at the hold or how many other aircraft are in queue.
There are two scenarios that give rise to the need for a small amount of flexibility. The first is that the push back and start went extremely quickly and the aircraft arrives at the hold 5 minutes before its CTOT margin (i.e. CTOT minus 10). All aircraft behind it in the hold get held up by delaying that 1 aircraft, and it's possible that another aircraft may miss its slot as a result.
The other scenario is that an aircraft arrives at the hold just before CTOT plus 10 minutes, but a landing aircraft reports debris on the runway meaning that a runway inspection is required, or perhaps there is just a lot of congestion at the hold. Is it really sensible to make the aircraft that's missed its slot taxy back to stand and refuel rather than let it go at CTOT plus 12?
Whilst I realise that you have to draw the line somewhere, it seems sensible to me that once the aircraft is in the system with engines running that it should be allowed to continue if it's only a couple of minutes off of its CTOT margin. If necessary slap it with a speed control, but don’t let it miss the slot and wait for a new one with engines running.
As I said before, ATC are usually extremely good at getting it just right and making sure that everyone arrives at the hold, in the correct order and within the correct time frames provided of course that the aircraft was ready to start on time.