International Operations Manual

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.

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

Last revision:




Eurocontrol Member States (2015), from Basic CFMU Handbook.

Flight Plans

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):

  1. provides a centralised flight planning system for the States within the CFMU area with the object of rationalising reception, initial processing and distribution of flight plan data to ATC Units;
  2. provides Repetitive Flight Plan (RPL) and Filed Flight Plan (FPL) data for use by the CFMU Operations for ATFCM planning, monitoring and slot allocation.

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.

[ FAQs] When do I file an FPL? Not later than 3 hours before EOBT. You will get either:

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

  • REJ (FPL rejected).

Slot Allocation

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, ¶] 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).

Slot Tolerances

The CTOT is valid from CTOT - 5 to CTOT + 10.

Dealing With the System

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, 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.


[ 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 the SAM has not yet been issued, you can send a DELAY message.
  • If the SAM has been issued, you may need to CANCEL your flight plan and restart the entire process.
  • SSR (Slot Revision Request)


If you want to depart early, you have several options:

  • You could send a cancellation message (CNL), wait 5 minutes, and resubmit. This could get you an early time but it risks a time even later than your original slot time.
  • You could just wait until the issued slot time.
  • You could send a REA (Ready) message, which tells the CFMU you are ready to take the next available slot. But you need to ensure you are really ready with everyone loaded. You also need to make sure the airport can accomodate you. If the airport has its own slot procedures, you could find yourself with a CFMU slot that does not agree with the airport slot. You need to ask the airport. A knowledgeable handler can work both ends of the equation to minimize this possiblity.

Improving Your Slot Time

[ 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.

Missed Slot

[ 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.


[ 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).

Slot Cancellation

[ 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.

If You Don’t Have a Handler

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.

See Also: