Eddie sez:

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.

In a nutshell, here is how it is supposed to work:

  1. You tell "them" when you are going to be ready with a "Target Off Block Time" (TOBT), when you will be ready with all passengers on board, doors closed, ready to start engines.
  2. "They" give you a "Target Start Up Approval Time" (TSAT).
  3. You call "them" when ready to start.
  4. "They" look at all the traffic throughout Europe to make sure the airways and airports do not become saturated during the time you are moving. If there is going to be any saturation, "they" will issue slot reservations to make sure the system isn't overwhelmed.
  5. "They" can simply delay you or even re-route you.
  6. Getting slotted may be no big deal, or it could ruin your day. Knowing how to handle it all improves your odds of avoiding that last possibility.

Everything here is from the references shown below, with a few comments in an alternate color.

Note: The Eurocontrol people like their acronyms, but it is a foreign language to many of us. Breaking with convention, I'll explain each acronym as it comes, repeatedly.

Last revision:


What's the big picture?


Photo: Milestone approach, FMP Exchange
Click photo for a larger image

[ATFCM Users Manual, ¶3.1] Air Traffic Flow and Capacity Management (ATFCM) is a service that is enhancing ATFM with the objective of managing the balance of demand and capacity by optimising the use of available resources and coordinating adequate responses, in order to enhance the quality of service and the performance of the ATM system.

You can be forgiven for thinking, "That's as clear as mud!" The process is designed for the people doing the slot allocation and they are primarily interested in the airlines. If you have a good handler, or at the very least a good international trip support service, this should be transparent to you. But even if all that is true, you need to speak the language. I have had to negotiate slots without any help just a handful of times. In each case it was a matter of talking with someone on ground control or making a phone call to a number that I got from ground control. Just knowing what to say and when is half the battle.

"You," the Aircraft Operator (AO), communicate with "them," the Central Flow Management Unit (CFMU), with messages. This is easier than it sounds. For example, you send a ready message, "REA," by asking ground control to do that for you. LIke this, "Ground control, November One Two Three requests you send a ready message. We are ready to go now."

When do I File my flight plan?

[ATFCM Users Manual, ¶2.2] As per ICAO rule from ICAO doc 7030, flight plans for flights which may be subject to ATFM shall be submitted at least 3 hours before the EOBT. You will get either:

  • ACK (FPL accepted) or,
  • MAN (errors in FPL; after manual processing you will get either ACK or REJ) or,
  • REJ (FPL rejected)

[ATFCM Users Manual, ¶8.1.5] FPLs sent to the IFPS less than 3 hours before the EOBT will render those flights as “late filer”. These flights may be penalised during the slot allocation process. In the flight status column (STA) of the flight list in CHMI / NOP Portal these flights can be identified with a “LF”.

Translation: You should file your flight plan at least three hours prior to your Estimated Off Block Time (EOBT), which is the time you plan on starting your taxi after engine start and before takeoff. You should be told the flight plan was accepted with an ACK message. They could come back and say they had to manually edit the flight plan with a MAN message and that sets you up again for either an ACK or REJ message. If you get a MAN and an ACK, you need to examine the flight plan because it may have changed. In any case, a REJ message means the flight plan you submitted isn't going to work and it is up to you to revise it.

It is unclear how a flight is penalized for late filing.

When do I have to notify "them" of a delay or desire to go early?

[ATFCM Users Manual, ¶2.2] As per ICAO rule from ICAO doc 7030, any changes to the EOBT of more than 15 minutes for any IFR flight within the IFPZ shall be communicated to the IFPS.

Translation: If you think you will be more than 15 minutes early or late from the time you estimate your will be ready to taxi (Estimated Off Block Time), you have to let someone know. This applies to flights in the Integrated Initial Flight Plan Processing System (IFPS) Zone (IFPZ).

When do I find out I've been slotted?

[ATFCM Users Manual, ¶2.2] At the earliest, 2 hours before EOBT you will receive a SAM with a CTOT. However, if a regulation is applied after this time a slot will be issued immediately.

Translation: If you are to be slotted, you should find out 2 hours prior to your Estimated Off Block Time (EOBT) and that will come to you in the form of a Target Off Block Time (TOBT), a time where you should be ready for start up / push back, with all doors closed and ready to start engines. If you don't find out two hours prior, it is because a slot isn't required, but that might change. If that happens, they should tell you immediately.

How do I improve my slot?

[ATFCM Users Manual, ¶7.1] The RFI status indicates that the flight can accept SRMs with CTOT improvements. All flight plans are by default in RFI status. In case an improvement is possible, flights in status RFI will immediately receive a Slot Revision Message (SRM).

[ATFCM Users Manual, ¶7.2] The SIP Wanted Message (SWM) status allows the flight to receive a Slot Improvement Proposal (SIP), instead of directly receiving an SRM, when there is a possibility to improve the flight. The default status (RFI) may be changed to SWM status. Flights in SWM status are not affected by the Recover Hole mechanism.

Translation: Once you are slotted, you are automatically placed in "Request for Direct Improvement" (RFI) status and as soon as a better slots comes available, you should get it in the form of a Slot Revision Message (SRM). I am not sure of how asking for a Slot Improvement Proposal (SIP) through a SIP Wanted Message (SWM) makes things better, but it is an option. The Recover Hole Mechanism allows "them" to give you an open slot (the "hole") that suddenly becomes available.

How do I revise my flight plan or EOBT?

Translation: You can send a delay (DLA) message or a modification (CHG) message to communicate the need to change routing or timing.

What happens if I revise my EOBT after I've been slotted?

[ATFCM Users Manual, ¶2.2] If the new EOBT still enables the flight to depart according to its CTOT, the slot will not be recalculated. If a recalculation is necessary (e.g. DLA / CHG was received with an EOBT that places the ETOT after the CTOT tolerance window), the next available slot will be issued in a SRM. To avoid a substantial delay it is therefore important to update the EOBT as soon as practicable.

Translation: If your change doesn't impact the Calculated Takeoff Time (CTOT), then no problem. If it does, then they put you back into the process. You go to the bottom of the request list, but this isn't always bad. Let's say you want to go early and there happens to be an earlier slot that is empty because it was never assigned or someone else dropped out of it, well then it goes to you. But, on the other hand, if there are other airplanes who sent a CHG before you, well they get first crack at the new slot. Meanwhile the slot you were first given may be taken by someone else. The risk of sending a CHG is that you could end up with a slot that is worse than the one you started with.

What if I am ready early?

[ATFCM Users Manual, ¶7.3] For regulated flights being in a situation to depart before their CTOT / EOBT (doors closed and ready to depart), the AO may ask local ATC to send a Ready (REA) message or, in a CDM aerodrome, the TWR may send a TTOT (T-DPI-s) before the CTOT tolerance window (-5, +10). These actions will trigger the REA status for the concerned flight.

Translation: You, the Aircraft Operator (AO), can call up ground control or tower to send a REA (ready) message to let them know you are ready as much as 15 minutes early. If you want to go even sooner, I think you are supposed to submit a CHG message, but I've seen handlers work around this with an REA message.

What is my slot tolerance?

[ATFCM Users Manual, Annex 7] A slot is issued as a Calculated Take-Off Time (CTOT). The CTOT is defined as a time when the aircraft must take-off. The slot tolerance (-5’ to +10’) is available only to ATC and only to organise the departure sequence. If there is no departure sequence, the CTOT shall be strictly adhered to.

Translation: The slot tolerance is meant for tower to plan take off times as early as 5 minutes before and 10 minutes after the CTOT.

What happens if I miss my slot?

[ATFCM Users Manual, ¶2.2] If your new EOBT is known, send a DLA / CHG. You will receive either: SRM, SLC or FLS. If your new EOBT is not known, send a SMM. You will receive an FLS and will remain suspended until you send a DLA / CHG to provide your new EOBT.

Translation: If you can provide a new Estimated Off Block Time (EOBT), do that. They will respond with a Slot Revision Message (SRM), a Slot Cancellation Message (SLC), or a Flight Suspension Message (FLS). If you cannot provide a new EOBT, you get the FLS. A SRM gives you a new slot time. A SLC means the entire need for slots has gone away. An FLS means you probably have to refile.

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