How to Manage Traffic Without A Regulation, and

How to Manage Traffic Without A Regulation, and
What To Do When You Need One?
Identification of the Issue
The overall aim of NATS’ Network management position is to actively manage traffic
so that sector and unit throughput is maintained at a safe level whilst maximising
available capacity and minimising disruption to our customers.
NATS’ Network Management uses two main systems to identify capacity issues and
to make judgements as to the best way to manage them. These systems are the
CFMU CHMI and NATS own Traffic Load Predication Device (TLPD). Both these
systems use the same base data; however the analysis and display is different.
Based on experience, NATS’ Network Managers compare the output from both
systems to provide the mental picture of the situation on which decisions are based.
The CFMU CHMI is used primarily to provide a long range (4-10 hours) sense of the
anticipated traffic situation in the sector (or combination of sectors) and provide UK
Network Management with a feeling as to where to concentrate in the forthcoming
period. The method of display commonly used for CHMI (20mins/rolling hour) tends
to amplify any perturbations in airspace throughput and thus provides a good overall
demand ‘landscape’.
Figure 1: Screenshot of CHMI
TLPD displays traffic demand up to four hours ahead, and this is the timescale UK
Network Management will tend to act upon as the majority of Europe wide
disturbances will have impacted the overall demand picture thus it is a truer reflection
of what is expected. At this point UK Network Management will actively monitor the
situation and start to formulate plans, however in the majority of cases plans won’t be
acted upon until the traffic situation is less than 2 and a half hours away as slots will
have been issued for UK departures at this point and the final outlook better known.
Figure 2: Screen shot of HMI (With explanatory indicators)
MONITORING VALUE – ENTRY PER HOUR
SECTOR OCCUPANCY - PER 15 MINS
A/C OCCUPANCY
ROLLING TIME LINE - 4 HOURS
CURRENT TIME
HISTORICAL DATA
15 MIN BLOCK
COMPLEXITY
From experience, what may appear as an hour or more of demand in excess of the
Monitoring Value on CHMI may well manifest itself as a single peak on TLPD and
thus a regulation would impact far more traffic than is necessary. Using TLPD UK
Network Management gains confirmation and confidence in the outlook present by
CHMI.
To Regulate or Not
The judgement call as to whether to regulate or look for alternatives is mainly based
on the use of TLPD. TLPD displays traffic as discrete 15 minute columns of airspace
occupancy (whereas CHMI shows airspace entry) so UK Network Management will
look at the level and duration of the excessive traffic situation. If the excess is
confined to 2 or 3 columns (30 to 45 minutes) then a non-regulated solution will be
sought, however if the situation is more prolonged then a regulation will be more
likely to be used.
Ultimately a regulation is always available as a solution to the problem, and there are
no hard and fast rules as to where and when to apply them. An important caveat to
the preceeding sentence is that a regulation may not be effective if applied “at the
last minute”. The decision is always based on experience and analysis of the traffic
that makes up the excessive traffic situation.
Within the UK Network different sectors have different problems and different
solutions to resolve them. Through local experience UK Network managers can
chose the solution that is most effective and has the least impact to safely achieve
the desired result. As an example, the use of departure metering (through processes
such as Minimum Departure Interval – MDI) is more effective resolving a problem
close to the departure aerodrome whereas at greater distances from point of
departure, other factors (winds, aircraft speed, vectoring and using direct routings)
diminish the effectiveness of this process.
Local experience also enables UK Network Management to know which sectors are
closely linked and how a particular bulge in traffic demand can often be mapped
through a series of sectors, and the most effective point of action chosen to resolve
multiple problems.
Any decision making will always involve the Local Area Manager for the relevant
airspace. This individual provides a much greater understanding and level of detail
to the decision, with UK Network management adding the ‘network wide’ implications
and offering the potential solutions. On many occasions the Local Manager will
decide that the issue can be handled without intervention and brief the operational
staff accordingly.
Once a decision has been made the situation is continuously monitored to ensure
that any changes in demand can be handled safely and that the impact to NATS’
customers is minimised.
Making the Decision
Where a bulge in demand is identified and the duration does not necessarily warrant
regulation, UK Network Management will undertake a number of activities to confirm
the situation and gain a deeper understanding of what is happening and why. This
process is based around the Flight List which displays all the traffic contained within
the demand bulge for the airspace concerned.
Often TLPD data has a number of inaccuracies within it that need to be resolved to
aid the decision making process. Flight lists will be examined to identify any aircraft
that should have departed but have not yet – and the EOBT updated accordingly The
differing colours of columns in Figure 2 indicate the sources of the information from
which data consistency can be extrapolated.
Once the data has been updated, the flight list will be examined and any obvious
trends identified. This could be a prolonged sequence of departures from a single
airfield; the combination of closely spaced departures from a group of sectors, etc.
The UK Network Manager will examine this and make a decision as to whether the
presented traffic situation can physically manifest itself – as the data is at this point
based on flight plan information it is possible to show 10 departures from the same
airfield at the same time. This is physically impossible and regulating based on this
would be unnecessary penalising.
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Figure 3: Typical Flight list
What To Look For
When examining the flight list UK Network Management look for any consistent
trends or unusual situations that have contributed to the problem. This may be a
sudden surge of traffic from a particular point on the continent (such as will occur
when a severe regulation ends and traffic is allowed to free flow through the
previously effected airspace) or a stream of departures from an individual airfield.
By examining the flight list UK Network Management gets a sense of what is likely to
happen and can structure their response accordingly. UK Network Management will
identify traffic within the sector that does not necessarily need to be there, such as
departing traffic that can be accepted in but can stay with a sector below the airspace
or landing traffic where the descent point has been calculated but they could pass
over the top.
In the event that the problem is a result of a stream of departures from a single point
these can be metered by using MDI (a rigid process), Average Departure Interval –
ADI (a less rigid process that still provides a level of assurance on delivery), or
Airfield Reasonable Departure Spacing – ARDS (where the airfield will use their ATC
understanding to provide an appropriate departure sequence whilst retaining a lot of
operational flexibility).
Which of these processes is used will depend on the overall traffic pattern and the
experience of UK Network Management as to which will be most effective.
Whilst the above techniques are all time based, depending on the airfield and
situation UK Network Management may request a distance based solution, using
Miles In Trail (MIT) from a single or group of airfields delivering into the effected
airspace.
When the bulge in demand is shown in a vertically layered sector UK Network
Management will look at the demand levels in adjacent sectors, to see if targeted
level capping can resolve the situation. Often by limiting the climb profiles of a small
number of flights, to position them into airspace where there is available capacity,
this will avoid regulations that have a much more widespread impact.
In some circumstances UK Network Management will look at the possiblity of
tactically re-routing a small number of flights to have the same effect – negotiating
directly with the airlines and gaining their understanding and approval of why this
action has been taken.
In the event that the bulge in traffic is shown as a single 15 minute period of high
demand, the traffic may be manipulated to spread the impact in a more manageable
manner.
This may mean delaying aircraft on the ground. By issuing Take Off Not Before
(TONB) instructions, direct to the ATC unit at the departure airfield, we ensure the
specific aircraft arrive in the airspace slightly later than originally planned and when it
is more acceptable in terms of demand. TONB instructions would typically be for a
maximum of 5-7 minutes and, unlike regulated slots, are targeted at specific flights.
With all the above techniques, UK Network Management continuously monitor the
situation to determine whether the chosen course of action is effective and where the
impact on NATS’ customers can be minimise whilst maintaining a safe operation.
If We Have To Regulate
There will always be instances where a regulation is required to safely manage traffic
demand, and UK Network Management will use this method where it is appropriate.
Once a regulation has been applied, by CFMU, UK Network Management review the
flight list, affected by the regulation, to see what improvements can be made. In
particular they look for flights that are not actually worked by the controlling authority
of the airspace but are captured within it by the airspace descriptions used by the
CFMU.
They look for flights that could be tactically level capped or re-routed to avoid the
airspace and thus regulated delay. Where a flight has a disproportionately high delay
the reasons for this will be identified (missed slot or late filing of a plan etc.) and this
reduced where it can be safely handled within the sector.
These activities are taken to reduce the impact of the regulation to all users whilst
maintaining capacity in a safe manner.
Benefits of Tactical Capacity Management:
Since the concepts and techniques behind network management have evolved over
a number of years it is difficult to gauge the direct impact of tactical capacity
management to show how much additional traffic is being accommodated or how
much delay is avoided.
Instead the benefits of tactical capacity management can be illustrated in the support
of all stakeholders, providers and customers, in the processes and actions used by
the UK network management.
In an attempt to provide a simplistic quantification of the benefits to airlines provided
by the application of tactical capacity management consider the following:
On the morning of 31st July 2008, because of technical difficulties with the TLPD, the
UK network manager asked CFMU to ensure protection of the UK sectors by
imposing regulations. When the effects of the regulations were calculated on the
expected traffic it was anticipated that over 12,500 minutes of delays would be
created within the UK airspace.
As the TLPD system came online and the network managers were able to examine
the characteristics of the expected traffic, they were able to ask the CFMU to lift
regulations in a measured fashion, without creating sector overloads.
Using tactical capacity management procedures the UK network managers were able
to lift replace regulations with precise tactical capacity measures targeting specific
aircraft. By the time that all the regulations were cancelled, actual delays were limited
to just over 4,500 minutes, a saving to the airlines of approximately 8000 minutes.
Using the recognised conversion of 1 minute delay equating to €70, this represents a
saving of €560,000 to the airlines in one day.
Further Information on NATS Network Management:
Contact:
David A. White
Head of Network Management Strategy & Development
NATS
+44 (0) 1489 612429
Email: David.A.White@nats.co.uk