Flow control is a way of life in the EU; the skies have become so crowded that something had to be done. In 1988 the entire system was automated which enabled more airplanes to fill the sky more efficiently, but it made a complex system too complex for pilots to comprehend.
Even if a pilot was emersed into the system for complete familiarity, pilots aren't allowed to access the system directly. And there is that pesky problem with language. It really pays to have a local handler on your payroll everywhere you go in Europe. But there may be times the handler is unable or unwilling to help. In that case you need to be able to speak the CFMU lingo. There are a lot of acronyms. If you learn the terms, are patient, and remain calm on the phone and radio, you too can negotiate a slot in the European Union.
Everything here is from the references shown below, with a few comments in an alternate color.
Eurocontrol Member States (2015), from Basic CFMU Handbook.
The process begins when you file your flight plan, which you can do up to 120 hours in advance but should do no later than 3 hours prior to your desired takeof time. (If you file more than 24 hours in advance, you will need to add the DOF -- Date of Flight -- entry into item 18 of the flight plan.) From this point, your fate is in the hands of the Central Flow Management Unit (CFMU).
[CFMU Handbook, ¶7.4] Integrated Initial Flight Plan Processing System (IFPS):
Every flight plan ends up with the IFPS to be deconflicted so that, in theory, once you takeoff there should be no conflicts with any other en route traffic or with the volume of traffic at your departure and destination airports.
[https://www.eurocontrol.int FAQs] When do I file an FPL? Not later than 3 hours before EOBT. You will get either:
By the time it gets to the pilot, a MAN result means the flight plan was accepted, but with minor changes. If the flight plan was sent back to the IFPS for manual adjustment that failed, the pilot would see that as a REJ.
If there are no en route conflicts or no flow issues, your flight plan can be accepted without a slot and you are free to depart unrestricted. If a slot is needed, it will be generated by the Computer Assisted Slot Allocation (CASA) system.
[CFMU Handbook, ¶11.2.1] The CASA System is largely automatic and centralised, and functions from an Aircraft Operator’s point of view in passive mode.
[CFMU Handbook, ¶188.8.131.52] At a fixed time before the Estimated Off-Block Time (EOBT) of each pre-allocated flight, called Slot Issue Time (SIT), the slot is allocated to the flight and a Slot Allocation Message (SAM) is sent to the Aircraft Operators and ATC.
The CFMU issues the slot 2 hours prior to your EOBT by sending the SAM. You will also get an Expect Start Engine Time which considers the time to do that and the time to taxi when arriving at a Calculated Takeoff Time (CTOT).
The CTOT is valid from CTOT - 5 to CTOT + 10.
Generally speaking, only an airport official or somebody associated with the system between the airport and the CFMU can make changes to an allocated slot. Eurocontrol can be contacted (numbers and email address are given at https://www.eurocontrol.int), but the first question will likely be “have you called the airport?” Your handler should be your “go to” contact. Failing that, you should talk to clearance delivery, ground control, or someone else at the airport first.
[https://www.eurocontrol.int FAQs] FPL updates - When do I notify a delay? Send a DLA/CHG for any change of EOBT (Estimated Off Block Time) greater than 15 minutes. However, do not update EOBT as a result of delay given by CTOT (Calculated Take-Off Time).
If you cannot make your SLOT time, you should cancel it to free that time up for other aircraft. It is said that the CFMU tracks operators who are habitually unable to make slot times and can penalize you in the future.
If you want to depart early, you have several options:
[https://www.eurocontrol.int FAQs] Change status - How do I change status of my flight?
By sending : an SWM (SIP Slot Improvement Proposal) Wanted Message), if you were in RFI (Ready/Request For (direct) Improvement ) status or an RFI, if you were in SWM status.
Remember the airport has to do this for you, either through your handler or your request.
[https://www.eurocontrol.int FAQs] What do I do if I have missed my slot?
If your new EOBT (Estimated Off Block Time) is known send DLA/CHG. You will receive either: SRM (Slot Revision Message), SLC (Slot Requirement Cancellation Message) or FLS (Flight Suspension Message).
If your new EOBT is not known send an SMM. You will receive an FLS (Flight Suspension message) and will remain suspended until you send a DLA to provide your new EOBT.
[https://www.eurocontrol.int FAQs] How can I reroute my flight?
Send a new route via a CHG (Change) or CNL (Cancel) and RFP (Replacement Flight Plan), or use AOWIR (Aircraft Operator ‘What-If’ Re-route) if you have access to ATFCM CHMI/NOP (Network Operation Portal).
[https://www.eurocontrol.int FAQs] What do I do if I get an SLC (Slot Requirement Cancellation Message)?
You are no longer subject to ATFCM measures and may depart without delay. If the SLC is issued after EOBT (Estimated Off Block Time) +15 minutes you must update your EOBT by sending a DLA/CHG.
Having a competent handler can save you hours of delay and make changes much easier. If you don’t have a handler or your handler pleads ignorance, start with ground control and ask, “I need help with a slot issue.” It is likely they’ve heard that before.
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