Like this ???
The negative of filing late is that you are more likely to get a slot from Eurocontrol. Slots are allocated starting at something like EOBT minus 3 hours.
I believe it is the most active airforce in Europe although I cannot recall it ever having been in combat
Na, na, Achim… 
Belgium is engaged in the Syria conflict with F16’s and has a very good reputation on NATO level with it’s fighter jet’s. It has quite some experience flying combat missions. Also during the Lybia crisis Belgium set up a substantial contribution….The aircraft though old where completely modernized with all the latest gizmo’s.
The area over the Ardennes is used by other NATO countries also I believe, it used to be for sure…
If there is flow control, you’ll get a slot regardless of when you filed, won’t you? But if you file early, you have a better chance of getting a slot that coincides with your EOBT.
Bookworm (and others) will know the detail on slot allocation but enroute slots are often caused by a controller’s sector filling up to the limit – regardless of the vertical separation. Then, slots are allocated according to how recently the flight plan was filed.
AFAIK just about all slots for UK to the east / south east are due to a limit in the Dover sector being reached. They are purely regulatory artefacts – there is no separation issue against lower airspace GA.
Slots are very much linked to specific sectors. A handful are responsible for 80% of the GA slots.
Belgium was giving out slots en masse this morning to our users with the justification “ATC equipment”. Seems that a few servers have not booted up yet
Zurich is the master of slots in Central Europe. When there is more than one aircraft within 1000NM of the sector, they issue “ATC capacity” slots to GA aircraft. We get it every day.
And then there is Cyprus which is the least competent ATC in all of Europe. You can’t do a traffic pattern there without a slot and they will make sure you fly doglegs over the open sea when the sky is completely empty. The Larnaca FIR is to be avoided…
Zurich is the master of slots in Central Europe.
I think you got it wrong. Try Geneva on a weekend during the Ski season. Or Berne, anytime 
Bookworm (and others) will know the detail on slot allocation but enroute slots are often caused by a controller’s sector filling up to the limit – regardless of the vertical separation. Then, slots are allocated according to how recently the flight plan was filed.
tomjnx and achimha have forgotten more about slot allocation than I’ll ever know.
My understanding is that the provisional slots enroute are devised 2 hours ahead, so all other things being equal there’s a bit of an advantage in filing at least 2 hours ahead if you want something close to an on time slot. However, I’ve never confirmed that with data, and I’m happy to take the advice of the experts.
How late is “late” Achim?
I personally think that filing 2-3h ahead works well. Of course with sufficient time at hand should there be a problem. You need 2h per regulations but in reality even 5 min before EOBT works in almost all cases. If I file at 1600Z for the next morning, chances that a military commander schedules a little outing in the meantime are very slim.
Most of the GA slots disappear towards the original EOBT. One of the things I am planning to do down the road is a bit of data mining in our logs so we can give out hard facts about who allocates slots, how long the delays are and how they develop over time.
As to IFPS revalidation errors (the case jwoolard had, airspace use plan changed between filing and EOBT) — they are extremely rare. I think less than 1% of the flights we handle get it. Which means that filing a few days ahead isn’t that wrong either. One day I’ll collect another statistic sample: what is the average lead time of filing among our user base.
So today was fun…
Having got the flight plan in last night, I woke up this morning to a slot message (the ATC equipment issue above).
This slot time was then revised a total of 4 times, varying back and forwards by over an hour. In the end we only had 20 minutes delay.
Over Belgium I was twice given traffic information: F16 left to right 1000ft below. Never seen anything go by so fast…
Still, much much easier than doing that flight VFR.
Thank you for the excellent autorouter system. The SMS messages (12 for one flight!) saved the day.
