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- European CDM Substitution on Cancellation
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- European CDM Substitution on Cancellation
The Substitution on Cancellation process is proposed as an enhancement to
the current European Air Traffic Flow Management system.
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In cases of severe loss of capacity at an airport,
Substitution on Cancellation would help airlines to protect their schedules while
temporarily reducing demand for that airport to ease the disruption and reduce delays.
The following pages illustrate how ...
Collaborative Decision Making
Visit the European CDM website at www.euro-cdm.org for more information
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Introduction: Flow Management by CFMU
Where forecast demand for an area of airspace exceeds the available capacity, Europe’s
Central Flow Management Unit (CFMU) creates a regulation. A flight scheduled to pass
through a regulation is assigned a slot to constrain the time at which it reaches that busy
area. In this way, CFMU ensures that the airspace is not overloaded with traffic.
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If a flight is scheduled to pass through more than one regulation, each regulation will, in
general, require a different take-off slot. The regulation that requires the latest take-off time
is termed the Most Penalising Regulation (because it delays the flight the most). It is the
most congested area of airspace that flight passes through, and so takes precedence over
the others in setting the CFMU slot.
So a flight’s take-off slot is determined by its Most Penalising Regulation.
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On occasions, an airport’s movements capacity may be reduced to well below it’s normal
operating capacity, for example by fog or by an incident on a runway or taxiway. In order to
prevent a large build-up of arriving traffic waiting to land, CFMU will create a regulation,
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assigning slots to all flights planning to land at the airport.
If the airport’s capacity is severely reduced, the arrival regulation is likely to be the
Most Penalising Regulation for all arriving flights.
The next slide gives an example of large delays building up at a capacity-reduced airport ...
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An example of a capacity-reduced airport ...
Under normal operating conditions, our example Airport has an
arrivals capacity of 24 aircraft per hour
07:00
07:02
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07:05
07:08
07:10
07:13
07:15
07:18
07:20
Airport operations are disrupted, for example by fog,
07:22
07:25
and arrivals capacity is reduced by 50% to only
07:28
12 aircraft per hour (one every 5 minutes, on average).
07:30
07:32
Assuming the airport planned to operate at capacity,
07:35
there is now an over-demand of 12 arrivals per
07:37
hour. The flights scheduled to arrive in a single hour
07:40
07:43
now need two hours to arrive.
07:45
07:48
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Large delays quickly build up.
07:50
07:53
A flight scheduled to arrive at:
07:55
08:00 will get an arrival slot of 09:00,
07:57
09:00 will get an arrival slot of 11:00.
08:00
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FLT001
FLT002
FLT003
FLT004
FLT005
FLT006
FLT007
FLT008
FLT009
FLT010
FLT011
FLT012
FLT013
FLT014
FLT015
FLT016
FLT017
FLT018
FLT019
FLT020
FLT021
FLT022
FLT023
FLT024
FLT025
 12 per hour
07:00 next step
07:05
07:10
07:15
07:20
07:25
07:30
07:35
07:40
07:45
07:50
07:55
08:00
Delays persist even after the airport returns to full capacity because there is a backlog of
delayed flights. This backlog will only reduce when there is spare arrival capacity compared
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with the planned number of arrivals - perhaps during the quieter afternoon period.
Cancellation
In the face of these severe delays, airlines may chose to cancel flights to help protect their
schedules. Cancelling a flight releases an aircraft and crew that would have been delayed
… on the flight into the disrupted airport
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… and again awaiting departure of the return flight.
When a flight is cancelled, its CFMU slot is released to be used by the next flight in the
slot “queue”...
…and all subsequent flights in the “queue” are brought forward one place to close the gap.
In our example, cancellation of 6 flights would reduce delays for subsequent flights by a
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total of 30 minutes.
Cancelling flights also helps Air Traffic Services and the Airport:
the best way to reduce the period of disruption resulting from the loss of capacity is to
reduce the number of flights going to that airport while the problem remains, and until
the backlog of delayed flights is cleared.
In our example, cancellation of 6 flights could mean that the backlog is cleared during the
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quieter afternoon period, instead of delays persisting into the busy evening period.
However, if a cancellation is made at the last minute, it may be too late for another flight
to take the released slot. As a result, the scarce arrivals capacity may actually be wasted,
with no reduction in delays.
In spite of this, the current European Flow Management system may effectively discourage
airlines from cancelling flights in a timely manner. The next slide illustrates how...
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How the current Flow Management system can discourage cancellations
Note that Airlines XX and YY both have
flights from the same departure airport (LHR)
at similar times.
CFMU slot time Under today’s Flow Management System,
at arrival
the first airline to cancel a flight is likely to
regulation
see its passengers (and hence revenue)
CFMU
New
transfer to the rival airline’s flight. The
Arrival
Slot next step
cancellation just releases a slot that will
Slot Time Time
help reduce delay for that rival flight.
10:55
The original arrivals schedule at our
example airport... next step
… and the delayed slots:
STA = Scheduled
Time of Arrival
Flight
Origin
STA
AB123
XX001
CD234
YY001
EF345
CDG
LHR
FRA
LHR
CDG
09:00
09:00
09:03
09:05
09:05
GH456
XX002
YY002
IJ567
BHX
LHR
LHR
BRU
KL678
XX231
MN789
OP890
XX003
QR901
11:00
11:05
11:10
11:15
cancelled
11:00
11:05
11:10
10:55
11:00
11:00
10:55
13:55
14:00
14:05
14:10
13:50
13:55
14:00
14:05
AMS
CDG
ZRH
12:00
12:00
12:04
15:25
15:30
15:35
15:20
15:25
15:30
BRU
LHR
DUB
16:00
16:00
16:02
18:25
18:30
18:35
18:20
18:25
18:30
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For example: If Airline XX cancels it’s
flight XX001… its CFMU slot is released to be
used by the next flight in the slot “queue”... next step
…and all subsequent flights in the “queue” are
brought forward one place and so get a slot
5 minutes earlier.
XX’s first arrival from LHR will
be at 13:55.
XX is likely to lose passengers to Airline YY
which can offer an arrival from LHR at 11:05
— passengers from the cancelled XX001, and
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also from the delayed XX002.
Now Airline
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As a result, Airlines XX and YY may each wait
until the last minute to cancel their flights,
hoping that the other will cancel instead. next page
How Substitution on Cancellation helps
Substitution on Cancellation encourages timely cancellation of flights by allowing the
cancelling airline to benefit directly from the released slot.
This is achieved by a change in the slot allocation rules in cases of severe disruption at
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an airport.
Under Substitution on Cancellation, each slot is temporarily assigned to the airline
whose flight occupies it.
This means that an airline that cancels a flight can re-use the released slot, to reduce
the delay to another of its flights.
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 The airline is encouraged to cancel flights because it sees direct benefit from doing so
— and it does not see the released slot going immediately to benefit a rival!
 Airlines with several flights arriving at the airport are given more control in their
schedule management, enabling them to use cancellation to best effect.
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The Substitution on Cancellation slot allocation rules can apply only in cases of
severe disruption at an airport, because in that case the arrivals regulation is
the Most Penalising Regulation for all arriving flights (it is much more severe than other
regulations). Therefore, arriving flights can swap slots with very little risk of other
regions of airspace becoming overloaded as a result.
Re-running the previous scenario under Substitution on Cancellation ...
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Under Substitution on Cancellation ...
Each slot is temporarily assigned to the airline whose flight occupies it.
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If Airline XX cancels XX001 it can re-use the slot for an on-time arrival of XX002. next step
CFMU
New
Arrival
Slot
Slot Time Time
Flight
Origin
STA
AB123
XX001
CD234
YY001
EF345
CDG
LHR
FRA
LHR
CDG
09:00
09:00
09:03
09:05
09:05
10:55
11:00
11:05
11:10
11:15
GH456
XX002
YY002
IJ567
BHX
LHR
LHR
BRU
10:55
11:00
11:00
10:55
13:55
14:00
14:05
14:10
KL678
XX231
MN789
AMS
CDG
ZRH
12:00
12:00
12:04
15:25
15:30
15:35
14:00
15:30
OP890
XX003
QR901
BRU
LHR
DUB
15:00
15:00
15:02
18:25
18:30
18:35
18:20
18:25
18:30
cancelled
Now Airline XX can transfer passengers
from the cancelled XX001 to XX002, running
that flight full.
The passengers of XX001 are not delayed
any further by the cancellation of their flight.
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11:00
Furthermore, Airline XX can now use its freed
14:00 slot to help its delayed flight XX231,
scheduled for 12:00 arrival from another airport.
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That frees the 15:30 slot, but Airline XX cannot
use it, as this is before the scheduled time of
its next arrival.
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The 15:30 slot is therefore released back
into the ‘pool’.
As in today's system, each released slot
means subsequent flights’ slots are
advanced by a few minutes.
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Conclusion
Substitution on Cancellation left Airline XX in a better position after cancelling its flight
than the current Flow Management system would have.
Cancelling one early flight meant that Airline XX could significantly reduce the disruption
to the rest of its daily schedule.
 Passengers of flight XX002 had delay reduced by 3 hours.
 Passengers of flight XX231 from CDG had delay reduced by 1½ hours.
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 Under Substitution on Cancellation, Airlines with several flights arriving at the
disrupted airport will be able to use cancellation to better manage their schedules.
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This direct benefit to the cancelling airline will mean that:
 more flights are cancelled,
 cancellations are declared earlier, in time for released slots to be re-used.
And hence ...
 Delays will be reduced for other flights at the disrupted airport.
 Recovery from the disruption will be faster, benefiting Airport, Air Traffic
Services and user airlines alike.
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Notes
Substitution on Cancellation offers a way of improving today’s Flow Management system
in cases of severe disruption at an airport.
It has already been applied successfully in the US.
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Substitution on Cancellation is a good example of Collaborative Decision Making because:
• it encourages courses of action that are of mutual benefit to several parties
(cancelling flights benefits self and other airlines, Airport and Air Traffic Services);
• it puts the decision in the hands of the organisation best placed to make it
(Airline Ops decides which of its flights should be cancelled to best manage its schedule).
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As for all applications of CDM, participants will need to agree rules and procedures
to ensure that Substitution on Cancellation brings optimum benefit.
For example:
• Is only one single substitution allowed, or may the cancelling airline try to
re-use the slots released by each substitution (as was shown in the example)?
• Substitutions could also be negotiated between the Operations Centres of
different airlines, with the cancelling airline nominating another flight to benefit
from its freed slot. Should substitutions between different airlines allowed?
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