SESAR concept - recent questions answered

• Questions about the SESAR concept should be sent via e-mail to Ros Eveleigh.  Note: questioners remain anonymous.
• Where specific questions are discussed further, corresponding answers are refined and updated as necessary [in square brackets].
• Selected recently answered questions (in italics) are listed below. 

10 July, 2008

Are the TMR on the RBT fixed for the duration of a flight?

[Not necessarily.  The TMR are not constraints on RBT but a way of achieving a balance between trajectory uncertainty and the overheads of RBT updating]. The TMR will vary according to the needs of the ATM system for a given time or location and could be defaults carried by the airspace or the trajectory. The TMR could be expressed [as a 'delta'] in terms of time, climb rate or lateral/vertical position. The TMR may be tight for a portion of the trajectory where the traffic is dense, and looser elsewhere. Also, the TMR could be loose for a long lookahead time and tight where the lookahead is short, for example the TMR for the time at the FAF could be 5 minutes when the aircraft is 3 hours from the airport, but reduce to 30 seconds when it is 45 minutes away. [The benefit of variable TMR versus system complexity this causes needs to be established through R&D.] 

 30 June, 2008

How will CDM processes support SBT refinement?

When there is an over-demand that cannot be satisfied by redeployment of any available capacity, the problem is presented to the Users. The Users then balance their business needs to the new situation and submit new SBTs, possibly with the aid of a "what-if" tool. The input that will be provided by the ATM system to the CDM process that will solve the problem has not been detailed by SESAR, but could include: hypothetical delays that would be applied if no action were to be taken; probability of occurrence (less certain the longer the lookahead) and other factors to be defined that would support the User decision making. 

27 June, 2008

Is the RBT conflict free?

The RBT is not [necessarily] "conflict free". The rationale of the RBT is that it is agreed before take-off. The quality of data on aircraft position (along-track error) is therefore insufficient for separation assurance purposes.

[The RBT is agreed prior to departure on the basis of being the best balance between the needs of the airspace user and constraints of the ATM system, but not necessarily conflict free. When the RBT is executed, the authorised segments should be conflict free.]

When does the SBT become the RBT?

The SBT is the published business trajectory that is available for collaborative ATM planning purposes, whereas the RBT represents the trajectory that the User agrees to fly and the ANSP and Airports agree to facilitate. The SESAR concept does not specify a time or external trigger when the SBT changes to an RBT. When airports and ATM have agreed on the trajectory to be flown, the data will be loaded into the aircraft’s avionics. This final pre-flight trajectory generated by the on-board avionics is the RBT. 

 25 June, 2008

What is the difference between 4-D Trajectory Management and a 4-D contract?

4-D Trajectory Management is a fundamental principle of SESAR: it is the process that captures the overall traffic situation in the NOP and controls the development of the business or mission trajectories (BDT to SBT to RBT) in 4 dimensions (latitute, longitude, flight-level and time). Specifically, 4-D Trajectory Management is the process by which the Business Trajectory of the aircraft is established, agreed, updated and revised. This is achieved through Collaborative Decision Making processes between the aircraft operator, ATM and Airports (where applicable) except in time-critical situations when only Flight Crew and Controller are involved. [4-D Trajectory Management takes place from the time when the SBT is first shared until it arrives at the gate at its destination.] A 4-D contract is an ATC clearance that prescribes the containment of the trajectory in all 4 dimensions for the period of the contract during which the uncertainty associated with the future predicted position does not increase with the prediction horizon. 4D contracts are foreseen as an en-route control technique, and will not be issued pre-departure or in lower airspace.

23 June, 2008

How will Arrival Management change in SESAR?

Arrival management in the future (a significant evolution from today's AMAN) will consider traffic much earlier for the preparation of the sequence and required spacing to enable an optimal approach to be flown. The aim is to ensure an efficient descent portion of the RBT, undisturbed by tactical actions that might jeopardise the lateral or vertical efficiency of the arrival.

In the future scenario the airport will be served by a set of optimised arrival routes. The arrival manager function will be able to allocate arrival routes and set constraints such as Controlled Time of Arrival (CTA) on merging points with the objective of building an optimum sequence. The CTA technique fits well with Time Based Spacing (TBS) which would follow on after passing the CTA point.

The arrival manager could work as follows: 

1. As aircraft arrive at the arrival manager horizon, the RBT is reviewed and an alternative trajectory may be considered along with a CTA for a merge point.
2. If aircraft take-off within the arrival manager horizon, their agreed RBT will be influenced by the arrival manager function, which might apply a constraint on a point in the vicinity of destination (such as a target time) with the aim of preparing the arrival sequence. When the aircraft becomes airborne, a CTA is applied.
3. Aircraft may be required to fly trajectories that are laterally or vertically separated to avoid having to apply in-trail speed control, which might prevent the CTA being respected - a good reason for the deployment of closely spaced PRNAV routes. 
4. As the aircraft approach the CTA point, they will make the transition to TBS and follow the aircraft ahead with the required spacing.
5. The lateral and vertical trajectory is therefore respected throughout the process enabling the most efficient arrival trajectory in all but speed, which is used to optimise the sequence and achieve the ideal spacing. 

The use of improved trajectory data allows the arrival management process start earlier to deliver traffic efficiently into the structured arrival route system at the optimal place and time, which will enable all of the above to happen with minimum tactical intervention. Therefore, the preparation of the arriving traffic sequence is expected to be completed by around 20 mins prior to touchdown, and should start only as early as necessary to achieve the stated objectives. It is thought that at least 1 hour will be needed to smooth out ripples in the traffic delivery, which will be the result of RBT, which is expected to be +/- 2 or 3 minutes.

For information, the UPS hub operation in the USA starts to do arrival management 1000 NM out and is now addressing the problem of integrating departures from airports within this range. 

19 June, 2008

In 2020, will the Tower Runway Controller change the sequence of aircraft presented by the DMAN?

It is anticipated that the DMAN will generate an optimal sequence (including spacing) taking into account all constraints, e.g., RBT constraints, wake vortex categories, etc., and the routine task of Tower Runway Controller will be to respect that sequence.

The highly dynamic nature of airport operations means that the system will allow the Tower Runway Controller to make changes to that sequence when required.

The AMAN will work with shared data that enables the automatic consideration of the output of UDPP. That is, the arrival management process envisaged by SESAR will take into account user preferences by access to the outputs of the UDPP. 

1-12 June, 2008 

Are Tower and TMA Controllers aware of the Network Operations Plan (NOP)?

Yes, the NOP is instantiated through the RBT, which will be available for each flight, much as the flight plan information is available now. The proportion of RBT information available to particular users of the system has not been decided.

Do tactical controllers have responsibility for delivery of this plan, subject to the main priority of safety?

Yes, the RBT in the plan is the trajectory that the ANSP has agreed to facilitate, so delivery-to-plan must be a responsibility of the tactical controller. [It is not clear at this time how much visibility of the overall plan the controller needs.  When there is deviation from the plan, this will be recognised by the system which will analyse the situation and may or may not require the controller to take remedial actions.] 

Or is it the responsibility of the aircraft operator to keep to the plan?

Yes, it is the RBT that the aircraft operator has agreed to fly; however, the concept recognises that circumstances may occur that prevent an operator from keeping to that plan. In these cases, the RBT will need to be renegotiated, possibly causing the UDPP to be invoked or other collaborative planning actions deployed.

Will an aircraft receive an inferior service if it arrives before or behind plan?

[If the aircraft arrives before or after any constraints applied to the trajectory, it will not receive the service agreed.] 

Or will the operator be penalised the next day?

The SESAR concept does not describe the application of penalties on the operator (or service provider) for not following the RBT. 

18 April, 2008 

What is the difference between Dynamic DCB and Complexity Management?

The actions of Dynamic DCB and Complexity Management both react to traffic loading prior to its entry into a sector.

Dynamic DCB can have impacts at local and network levels. As the look-ahead for decisions is up to 2 hours, these will be based on less-certain data as a proportion of aircraft involved may be on the ground at the time of forecast.

Complexity Management decisions apply actions at ATC local-level based on forecasts of aircraft already in flight, which therefore use more precise data, with look-ahead of around 40 minutes prior to sector-entry and could result in minor adjustments to flight profiles.

Dynamic DCB solutions will be more adapted to solve traffic demand/capacity imbalances.

Complexity Management is only expected to be necessary in specific regions of very high traffic density and is therefore an optional layer of the ATM process to be deployed only when fully justified. Unless deployment of Complexity Management can be justified Dynamic DCB alone will ensure acceptable traffic levels whilst maximising performance.

7 March 2008

What are the rules and incentives (if any) for Pilots, Aircraft Operators, Airport Controllers and Radar Controllers to conform to the Network Operations Plan (NOP)

The NOP incorporates the Reference Business Trajectories (RBTs) for aircraft; these represent the 4D trajectory that the aircraft will fly and the airports and service providers facilitate. It will therefore be possible to monitor compliance [with constraints] by any party. The SESAR concept does not define rules or incentives to have an acceptable level of compliance, but does not rule them out.

If UDPP meets at an airport and collaboratively revises the Airport Operations Plan, does it have to conform to the current state of the NOP (cf. respecting Flight Plans and CTOTs today), and does it have to negotiate with AMANs and DMANs at all connected airports?

UDPP is a CDM process activated by Network Management. The initiation of UDPP includes an initial attribution of delay. New proposals coming from the Airspace User should respect other constraints included in the NOP (i.e., if UDPP is activated for a departure queue the Airspace User cannot ignore destination constraints in his SBT recalculations that may result from UDPP departure “slot swapping”)

If there is no constraint on departure time for any flight outside the AMAN horizon for its destination, how is it possible to manage complexity?

The need for time constraints for aircraft outside the AMAN horizon will be dealt with by the layered planning processes. The result of this process will be implemented through the RBT. 

4 March 2008 

When refining Shared Business Trajectories (SBTs), many other SBTs could be affected. Would SBTs under revision have a special identifier for making it easier to airspace users affected by the revisions have a clear picture on which trajectories are still undetermined?

The notion that the SBT will have different status in the NOP is not ruled out in SESAR, but the need for and scope of the information on SBT status will require validation to ensure the right level of information is available, not too much, not too little.

How will PTC-2D exactly be carried out? What is the difference to today? It is a new separation mode. How is it applied for separation? What are the responsibilities? Where is it applicable?

2D PTC may be used to authorise a segment of the RBT in 2 dimensions. It is also a means of creating a closed loop route revision that is designed to be flown with an agreed precision. It is designed to replace the use of open-loop routing instructions such as headings or “fly track”. It can therefore be used to create a discrete 2D route for a particular aircraft to resolve conflict. The separation to be applied should be similar to that applied to “separated” PRNAV routes. It is expected that with suitable track conformance monitoring this separation should be similar to radar separation minima – but it is not radar separation minima.

How will PTC-3D exactly be carried out? What is the difference to today? It is a new separation mode. How is it applied for separation? What are the responsibilities? Where is it applicable?

3D-PTC is exactly the same as 2D-PTC except that it prescribes a 3rd (vertical) dimension. Therefore all 3 dimensions must be flown with the agreed precision and the separation minima in the vertical plane should be that applied to “separated” vertical transition paths. This is a new separation minima because aircraft today are provided with separated level bands (current level to cleared level) except where climb rates (climb not less/more then) techniques are applied.

3 March 2008 

How will ATC Clearances be issued for each portion of the flight RBT?

The RBT will be authorised in segments using the trajectory sharing, revision and authorisation capabilities of the SWIM network. This process may be heavily supported by automation but with the separator (normally the Air Traffic Controller in Managed Airspace) central to the decision making process.

What is the process for a flight entering ECAC?

Prior to entering a segment of the RBT the aircraft will be authorised to proceed. This may be an automated procedure, but when conflict is identified along the concerned RBT segment the controller will be alerted and a revised clearance will be devised (with or without system support).

At what point are decisions made on runway sequencing, trajectory deconfliction, delay allocation and initiation of UDPP?

Runway Sequencing – at AMAN horizon 60-90 mins prior to destination
Trajectory Deconfliction – through deployment of route structure (dynamic or otherwise) or by dynamic RBT revision.
Delay Allocation - by Network Management processes - UDPP is one way. The rules determining when and when not to use UDPP will be pre-defined and available through the NOP.

What is at is strategic deconfliction?

Today, strategic deconfliction is achieved by the allocation of separated routes or levels. Traffic is separated tactically using such techniques as headings and temporary levels. In SESAR, this clear differentiation no longer exists with the elimination of current [open loop] tactical intervention techniques wherever possible. SESAR techniques include deconfliction by the deployment of advanced PRNAV route structures (2D and 3D) in dense traffic situations but in the all other situations separation will be assured by the use of new trajectory based separation modes in which aircraft will be provided with conflict free trajectory segments to be flown.