Slot Window Compliance

[bookworm]

On the CFMU portal, there's a graphic that shows "Slot Window Compliance". The current pie chart is fairly typical:

Complied 1045 (57%)
Dep. before 492 (27%)
Dep. after 295 (16%)

Am I misunderstanding what this means? The poor compliance percentage surprises me, as I thought that ATC would enforce the slot robustly, not permitting t/o before the slot, and requiring a DLA to be sent (precipitating a probable later slot) if the aircraft didn't make it away by the end of the slot. What's the real life practice?

[10W]

There could be some small level of inaccuracy due to local procedures.

For example, UK FMP positions have an agreement to vary the window by +/- 5 minutes if the aircraft is operating domestically and subject to a UK slot. This isn't co-ordinated with Brussels, so could show as a violation on their system even although it has been approved locally by the agencies involved. Other countries or ATS partnerships may have similar things in place.

There could also be some variance with timings, depending on how the CFMU calculates rounding up/down times. The UK rounds down if it is minute +29 seconds or less, and up if it is minute +30 seconds or more. Let's give you a CTOT of 1200. So if you get airborne at the end of your slot window of 1210 at 1210.29, then the UK will deem you departed at 1210. But it may be that the Brussels system says that is after 1210 and so you have violated because you departed at 1211 in their system. The opposite could also be true for an early departure, with the UK assuming you have taken off in the next minute (i.e. within the slot) at 1154.30 (UK time thus 1155) but Brussels deem you have gone a minute early as it is still 1154 to them. I don't have that detail of knowledge of the CFMU system, but it is a possibility.

Other than that, it seems to be down to the departure airfield for allowing the non compliance. Heathrow, for one reason or another, is usually top of the pops in the UK each day ;)

[Roffa]

Other than that, it seems to be down to the departure airfield for allowing the non compliance. Heathrow, for one reason or another, is usually top of the pops in the UK each day

Given that we're routinely over delivered when there's arrival flow in place it looks like the aggrieved parties outbound are not averse to getting their own back!

[10W]

Maybe we should just go for Free Flight now then ? ;)

[5milesbaby]

Are the stats for slots issued due to flow control, or are they also including being within 15 mins of a pending departure time during freeflow too??

I've been subject to an overload due to freeflow busters, 5 flights departed early, 5 late - one of which was 92 minutes after its P-time. Funnily 3 of the 5 late ones were the same company, they have now improved but still not angels. :ugh:

[10W]

That's another good aspect to investigate, 5milesbaby. There is a +/- 15 minutes on EOBT for non regulated flights which operators can use. It would be interesting to see if the CFMU data does indeed include such flights. I would expect not, but you never know !

[10W]

Having checked, the report states it is only for Regulated flights, and only for flights where the CFMU gets a DEP message or an Activation Message from the departure aerodrome.

The latest report is for February and it seems that Manchester Airport are now consistently the 'bad boys' in the UK with a slot violation rate almost double that of Heathrow (they were showing a similar level difference % wise in January also). Looking on the bright side, there's a few Turkish ones which are consistently even worse ;-)

[irishpilot1990]

Is it poor airmanship(or controller equivalent) or is there punishments/reasons for airports to not comply?

[5milesbaby]

That doesn't look good really then 10W, surely NATS should pick that up and address the violations through the UCE scheme? The only other excuse I can think for bad results is how often are Manch using their hourly slot extra tolerances (assuming they have them)? I remember that when I did famil at Gatwick, we could depart 2 an hour at +20 and 2 at +15 rather than the usual +10, I expect Manch has similar? Would the figures be able to show these extra allowed tolerances too?

Having stated earlier, being on the rough end of non-adherence isn't very pleasant and a practice that may well need nipping before it becomes too familiar.

[bookworm]

COMMISSION REGULATION (EU) No 255/2010 (http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:080:0010:0016:EN:PDF) (which I hadn't found when I posted above) sets out the responsibilities. It also says, under performance monitoring:

"Member States shall ensure that where adherence to ATFM
departure slots at an airport of departure is 80 % or less during
a year, the ATS unit at that airport shall provide relevant
information of non-compliance and the actions taken to
ensure adherence to ATFM departure slots. Such actions shall
be indicated in a report to be submitted by the Member State
concerned to the Commission."

So you have to fall below 80% even to get your wrist slapped! Though I do notice that Manch gets a mention as a bad boy in the 2010 report. ;)

[vespasia]

when I did famil at Gatwick, we could depart 2 an hour at +20 and 2 at +15

Long gone now, we're restricted to -5/+10, although tbh it's not usually a problem and Flow are pretty good at finding an extra 5 if we really need it for a good reason:ok:

[eagleflyer]

Although slot adherence should be insured normally there are occasions where it really doesn´t help but in fact worsens the result. In our center we´ve got quite a few routings that involve very short (repositioning) flights of 15-20 minutes. Sometimes there´s only one or two sectors involved in such flights, but still the TWR guys won´t clear a departure for take-off unless the CFMU has exempted the flight from the regulation. This takes a while of course (and sometimes serious discussions too) preventing us from using an opportunity the "real" traffic picture provides. This often happens during regulations due to WX.

[Gonzo]

Don't forget that application of MDIs and ADIs can in some circumstances overrule CTOTs, which might be a factor in CFMU's statistics.