achimha wrote:
The most widely used GA IFR filing solutions are (…). All of them relay they CTOT messages.
I’ve only used one of them up to now. I got CTOTs, but never a detailed explanation of why like Peter quoted in message 13. Is there a way to get them for light GA? My airline pilot acquaintances say they ask their ops department :)
You get the slot assignment/amendment message with all details when using autorouter. Sometimes you can draw conclusions from it and come up with an alternative route, sometimes it’s more difficult.
I am wondering what is the best strategy for enroute slots. Every once in a while we get allocated an enroute slot from Eurontrol which delays our departure. What I understand:
- Refiling, delaying etc. does not help as that puts you at the end of the queue
- Often it starts with an outrageous delay and then further messages come in and the delay settles to a more reasonable time.
- One strategy is to file early and then either leave late or delay at the latest moment. So in case a slot gets allocated it usually moves towards the actual time of departure.
Once an enroute slot is allocated what is the margin for leaving early or late around that slot EOBT? For example in Croatia they let us depart 3min early but tower let us wait 1 minute on the runway not to exceed those 3 minutes.
What is the best strategy if you can not meet the slot departure time because of other delays? Lately we got allocated a slot only 3min after the original EBOT. Then we delayed by 30min for other reasons and the new slot was then 45min after the original EOBT. So maybe we should have delayed just by 10min and let the slot delay do the rest?
Hard question 
I usually got CTOT in range 5 to 10 min after filed EOBT if I file a night before the flight.
Sebastian_G wrote:
Once an enroute slot is allocated what is the margin for leaving early or late around that slot EOBT?
Keep in mind that a CTOT is a take-off time, not an off-block time.
You can take off from 5 minutes before to 10 minutes after CTOT.
Sebastian_G wrote:
- Often it starts with an outrageous delay and then further messages come in and the delay settles to a more reasonable time.
The problem is sometimes that you get a CTOT way after filed EOBT, and it then starts creeping forward until it is shortly after the filed EOBT. If you planned according to the first CTOT, you may not be ready by the time you got the revised CTOT… IIRC the autorouter has the /FREEZE feature (in the Telegram bot) which allows you to request no further updates to CTOT in order to avoid that.
I find that
Often it starts with an outrageous delay and then further messages come in and the delay settles to a more reasonable time.
is the most common scenario, so one has to be ready at the original EOBT and just sit around…
The exception is one of the ATC strikes (usually French, once it was a Greek one) and then the CTOT doesn’t shrink – until the strike ends. The only options are to cancel and route around the offending region or to file a VFR leg through it (which is a hassle if you have to depart VFR because you have to fly to/via VRPs, may not get into CAS, etc).
Essentially there is nothing you can do. File the time you want then if you get a slot hope it shortens. If you have one don’t delay or something to try to shorten it.
Normally +-5mins.
When a flight is regulated and a CTOT issued (slot, slot time) then there is no time margin for the AO.
AO must arrange for a departure on CTOT taking into account start up and taxi time. That means that in an aerodrome with a 5 min taxitime ATC have the right to deny start up clearance to aircraft requesting start up at the same time as the CTOT because the flight has missed the slot.
A time margin (Slot Time Window) that starts 5 minutes before CTOT until 10 min after CTOT is in the disposal of the ATC in order to sequence the flight in the aerodrome traffic. It is not uncommon for flights departing from the same aerodrome to have the same CTOT. It is their AOs responsibility to have the flight ready for start up according to their CTOT and the ATC job to sequence them in traffic and have them both airborne within the Slot Time Window.
A useful strategy from CFMU faq :
Slot – Can I ‘freeze’ my slot?
No. However, if the CTOT (Calculated Take-Off Time) received is acceptable, then a DLA (Delay) message should be sent to IFPS (Integrated Initial Flight Plan Processing System) using the following formula:
New EOBT (Estimated Off Block Time) must not be later than CTOT minus taxi time minus 10 minutes. Example: EOBT 1000, CTOT 1100, but the flight cannot go off blocks until 1025. The taxi time is 15 minutes. Calculation:
1100 – 15, minus 10 = 1035.
The new EOBT must be earlier than 1035, in order not to trigger a revised CTOT. Alternatively, you may change the status to SWM (SIP Slot Improvement Proposal) Wanted Message), which gives an option of accepting or rejecting any improvement offered.
It avoids having to wait in the aircraft for an hour if you are ok with the CTOT
Salim wrote:
the following formula:
New EOBT (Estimated Off Block Time) must not be later than CTOT minus taxi time minus 10 minutes.
How/where do you find the airport’s taxi time used by the Eurocontrol computer for this rule?
