How to Manage Traffic Without A Regulation, and What To Do When You Need One?

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 A/C OCCUPANCY SECTOR OCCUPANCY - PER 15 MINS ROLLING TIME LINE - 4 HOURS CURRENT TIME 15 MIN BLOCK HISTORICAL DATA 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. ν 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 31 st 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