I have just read somewhere that the penalty is a 1 hour hold, or a cancellation of IFR.
Is that real?
It seems somewhat bizzare for a Class G airport departure, because you are initially flying VFR, clear of CAS, on your own, and (usually) only in the general direction of where you want to be going. You call up the IFR controlling authority (e.g. London Control) when you get around to it. In some cases there could be a long VFR section of say half an hour (e.g. a departure from Biggin EGKB to the west). So the actual EOBT is not going to be well defined.
And if you depart from an airport in CAS, they won’t let you even taxi if there is a slot.
You’re misinterpreting what was written “somewhere”. What was meant was that because the destination had a limit on IFR arrival rate, the practical result of departing an hour before the slot was that the aircraft had to hold for an hour or cancel IFR and make a VFR arrival at its destination. It wasn’t a ‘penalty’ as such.
Never happens to us
Yes – the word “penalty” was wrong. There isn’t a Eurocontrol jail in the sky where they send pilots, with 2 choices: (a) to fly holds for one hour or (b) to cancel IFR and have to dig out VFR charts and hack along at 999ft across Belgium or whatever 
But to make you hold for an hour, for probably no reason (I don’t think any slots imposed on GA flying below about FL250 are done for any actual reason connected with traffic) because you ignored a CTOT seems silly. Still, I suppose they have to impose some sort of sanction otherwise why bother with slots in the first place.
Never happens to us
What doesn’t happen?
(a) You ignore slots but never get a hold
(b) You never ignore slots
If you ignore airport slots in Germany nothing will happen in the air but the slot office might send you a letter and threaten you with a very high fine.
Mostly b, sometimes a, but never a “punishment delay”
Sometimes there’s no choice if you are collecting someone and they’re late.
But if there is no sanction at all then the slot system is pointless. If they go to the trouble to issue an enroute slot you should comply. It can be a pain but so what? I actually don’t think that the issue them just because they can.
Airport slots are a bigger pain and often silly eg EDDB.
But to make you hold for an hour, for probably no reason (I don’t think any slots imposed on GA flying below about FL250 are done for any actual reason connected with traffic)
Not long ago, someone working for ATC explained to me, that most enroute slots within Germany are caused by understaffing of the control centres. They have very strict regulations regarding the number of aircraft a controller is allowed to handle at once (especially since the collision near Überlingen in 2002). So whenever someone calls in sick, the number of aircraft in some sectors needs to be reduced by issuing slots. In summer, the expected closure of sectors due to thunderstorms will also result in slots to avoid overloading the adjacent sectors.
To avoid problems associated with last-minute slots when departing on Z flightplans, I always try to get my IFR clearance while still on the ground. Either through the aerodrome radio operator or via mobile phone.
So far, I got only in (moderate) trouble for busting an airport slot at Zürich (with no consequences, they accepted our explanation), never for an enroute slot.
most enroute slots within Germany are caused by understaffing of the control centres. They have very strict regulations regarding the number of aircraft a controller is allowed to handle at once
That is the explanation which has been circulating for most of the slots issued to traffic departing southern UK to the east / south east. There is a claimed bottleneck in the Dover sector. I vaguely recall that the ATC desk is allowed to have 30 aircraft in that sector, so if you have 30 at FL300 and your filed route for FL150 is concurrent, you will get a slot.
Of course this is stupid… if the airspace wasn’t Class A then you could file Z until KONAN and fly it anyway. Well, you can file Z until KONAN at ~ FL064 under the Class A but (a) not in your jet and (b) it gives poor weather avoidance options because being held down low means one could end up under heavy wx through which one can’t climb up due to icing.
To avoid problems associated with last-minute slots when departing on Z flightplans, I always try to get my IFR clearance while still on the ground. Either through the aerodrome radio operator or via mobile phone.
That’s the holy grail Not always possible.
If they go to the trouble to issue an enroute slot you should comply
Everything within reason, though.
The only time I got an enroute slot (outside of Bern) was 5 minutes after a flight of more than an hour (due to ATC staffing). There’s no way I can control before departure where I will be exactly after one hour of flight, wind forecasts are seldom that accurate.
