Study of User Driven Prioritisation Process (UDPP)

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Study of User Driven Prioritisation Process (UDPP)

52ND ANNUAL CONFERENCE, Bali, Indonesia, 24-28 April 2013

WP No. 86

Study of User Driven Prioritisation Process (UDPP)

Presented by TOC


This paper investigates the concept of User Driven Prioritisation Process (UDPP). This new concept is designed to allow airspace users to have input into the allocation of delay in capacity constrained situations. UDPP will take advantage of other new concepts such as Collaborative Decision Making (CDM) and System-Wide Information Management (SWIM).

This paper proposes new policy on the subject.


1.1  User Driven Prioritisation Process (UDPP), aims to provide airspace users with more flexibility to re-arrange their schedule through airspace user driven prioritisation in a trajectory based environment (Eurocontrol), and is planned for implementation as part of SESAR Step 2.

1.2  UDPP is included in SESAR Work Package 7 – Network Operations. Work Package 7 covers services required to support trajectory-based operations, particularly in case of capacity issues.

1.3  ICAO ASBU Module No B1-35 – “Enhanced Flow Performance through Network Operational Planning” includes UDPP, estimated for global readiness in 2018.

1.4  The concept has also been suggested as a way to establish a market based approach to allocation of ATFM slots, allowing airspace users to tactically trade slots at the market price on the day of operation, so that individual airspace users can take into account their own business models and cost profiles, and trade slot times accordingly.

1.5  Specifically, it is intended for situations where an airspace volume or airport is operating below normal capacity, or there is an unexpected shortfall in capacity.


2.1 User Driven Prioritisation Process is an ATFM process designed to respect the business objectives of airspace users, while minimising the impact on the stability of the Network Management Function.

2.2  It represents a shift in allocation of flow priorities in capacity constrained situations where delays occur. In the existing environment the relevant service provider determines system capacity, and allocation of delay is managed by the ATM system. Under UDPP the service provider makes a determination of system capacity, allowing airspace users to express their preference for allocation of the delay.

2.3  By allowing airspace users to influence the allocation of delay, they are theoretically better able to arrange their operations to suit their business model.

2.4  Activation of UDPP is specifically intended for unplanned situations where an airspace volume or airport is expected to operate below forecast capacity. This could occur due to a number of reasons, such as un-forecast weather deterioration, partial airport closure, ATC staffing or other operational issues.

2.5  In the case of an unexpected reduction in system capacity, initial allocation of delay will be the responsibility of the Network Management. After allocation of initial delays by the applicable flow management unit, UDPP will be activated.

2.6  Following activation of UDPP, airspace users will be able to swap or trade their allocation of capacity through SWIM, under the oversight of Network Management. In the event that operators are unable to agree on allocation of capacity, then Network Management will impose delay. Responsibility for the stability of the ATM system rests with Network Management, and where fast-time simulation determines that the UDPP solution will have an adverse effect on network stability, a CDM (Collaborative Decision Making) process will develop an alternative.

2.7  ATM system capacity is constantly monitored by Network Management using SWIM and updates from Regional and Sub-Regional Network Managers, ANSP’s and Airports.

2.8  The UDPP design assumes that there are normally no enroute capacity constraints, thus UDPP delays are primarily a result of airport capacity constraints. The remainder result from isolated enroute constraints due to convective weather events. It is also assumed that arrival delays will be larger and more common than departure delays, and therefore arrival delays may be implemented as revised departure times to allow a flight to meet an allocated arrival time.

2.9  Example of arrival capacity constraint

2.9.1  When an airport arrival capacity constraint is identified by the airport operator, the airport operation centre (APOC) through the normal CDM process triggers UDPP. A declaration of capacity is made by the APOC through the Network Operations Plan (NOP), and the Regional Network Manager provides users with an hourly slot allocation in proportion to their schedule share (see 2.11)

2.9.2  If in an affected hour with a 50% capacity constraint, operator A schedules 10 flights, and operator B schedules 20 flights, then A will be allocated 5 slots and B will have 10 slots. Following the allocation, airspace users then coordinate with each other through SWIM to develop a distribution of slots suiting their mutual interests.

2.9.3  The outcome of the UDPP is published in the NOP and available to the Regional and Sub-Regional Network Managers, who then examine the impact on the network. The alteration of the natural sequence of aircraft may have impacts on the flow prioritisation of airborne flights, traffic synchronisation plans, sector loadings, departure sequences and so on.

2.9.4  If the UDPP is determined to cause an unacceptable level of instability on the network, then the Network Manager initiates a CDM process to redevelop the UDPP. In cases where the UDPP does not produce an agreed outcome, the Network Manager will impose the required constraints independently.

2.10 Example of departure capacity constraint

2.10.1 A departure constrained situation will be handled similarly to and arrival constraint situation. In the event that a flight is subject to both a departure and an arrival constraint, this will need to be assessed and may involve multiple rounds of negotiation.

2.11 Options for users to meet delays

2.11.1  A flight may be delayed on the ground, and fly a fuel efficient trajectory to meet the agreed Target Time of Arrival (TTA).

2.11.2  A flight may depart on time, and fly an inefficient trajectory to meet the TTA. Airspace Users may also continue to negotiate and trade slots after an aircraft becomes airborne.

2.12 Altering the UDPP solution

2.12.1 Once the UDPP solution has been determined and flights are airborne to meet the anticipated TTA’s, unforeseen circumstances may prevent some flights from meeting their time. In this case, the allocation of slots can be renegotiated either within the users own allocation, or by trading with other users to redevelop a solution that caters for the change in circumstances. The UDPP can therefore be seen as a continuous process following the initial trigger. The same renegotiation process will be initiated in the event of capacity changes following the initial allocation.

2.13 Compliance where multiple constraints exist for a single flight

2.13.1 If a single flight is required to meet TTAs for multiple capacity constraints, the number of negotiations and interested parties will increase rapidly. If a flight is subject to a departure constraint, one or more enroute constraints as well as an arrival constraint, it may not be possible for a solution to be found before departure. For this reason practical limits to UDPP need to be devised.

2.14 Penalties for non-compliance

2.14.1 To ensure that the effectiveness of the system, and to prevent abuse of self-regulation, there must be suitable tools to monitor and authority to penalise non-compliance with agreed times. Tools should exist to either impose additional delay or diversion to a non- compliant flight, which provide sufficient discouragement that their use is rarely required.

2.14.2 Compliance will also be analysed post-event to ensure UDPP participants have met the agreed times. Repeated non-compliance may result in exclusion from the program.

2.15 Tactical intervention by ATC

2.15.1  UDPP will only affect flow priorities for flights at the particular constricted node or airport. Normal traffic priorities and tactical intervention practices on the part of ATC will not be affected.

2.15.2  Where UDPP applies at an airport, the Arrival Manager will retain discretion to alter the sequence for the purpose of optimisation.

2.16 Existing relevant IFATCA Policy

2.16.1 The following policy is considered relevant to the studied subject:


IFATCA recognises the potentially dangerous situations that can arise when slot times are not adhered to.

In the EUR region ATFM utilises departure slot times as a means of regulating air traffic and that when a departure slot time is used, the time should be passed to the ATC unit at the departure airfield.

It is the responsibility of the aircraft operator to be ready for departure to meet the assigned ATFM departure slot.

Civil Aviation administrations pursue with the utmost vigour those operators who consistently fail to comply with ATFM measures.


IFATCA defines:

Sector Capacity: The maximum number of flights that may enter a sector per hour averaged over a sustained period of time, to ensure a safe, orderly and efficient traffic flow.

Occupancy Counts: the number of flights occupying a sector simultaneously during a specified period of time.


IFATCA supports the Controlled Time of Arrival concept provided;

  • Arrival Manager (AMAN) is available to define reliable CTA times.
  • RTA equipage level of aircraft is sufficient to support CTA operations.
  • Procedures and controller tools are available to integrate RTA equipped and nonequipped aircraft in the same traffic stream.
  • Tactical ATC interventions are always possible.
  • Accurate wind and temperature data is available.
  • Means to communicate the CTA contract with aircraft are available (preferably data link).


2.17 Implications for ATC

2.17.1  Demand and capacity management is a core function of ATM, and therefore any significant change to the process has potential to impact ATC operations.

2.17.2  Of the limited information, much of it is focused on the processes for determining capacity and allocating the slots, with very little consideration into the practical implementation of a UDPP solution within a live ATC environment.

2.17.3  The ability for operators to trade slot times after departure may cause additional workload and complexity for ATC sectors, specifically where an arrival sequence as agreed through UDPP varies significantly from an unaltered sequence.

2.17.4  Where a large delay is required to be absorbed enroute, a flight may request to either take an inefficient or longer routing, or change speed. Airborne rerouting may increase ATC workload and coordination requirements if appropriate tools are not provided.

2.17.5  Although Eurocontrol specifies that ATC will retain the authority for tactical intervention in all cases, there is potential for airspace users to place pressure on ANSPs to rigidly enforce agreed UDPP sequences, particularly if a market based approach is eventually established.


3.1  The UDPP concept is essentially a shift in the management of delay allocation, allowing airspace users to have input into the allocation of delay. The service provider continues to determine system/airport capacity and manage the allocated delay.

3.2  The UDPP process should be seamless to ATCOs, however, the potential exists for UDPP to have an adverse impact on ATC workload and traffic complexity due to dynamic changes in flight priorities and profiles.


It is recommended that;

4.1. IFATCA Policy is:

Dynamic slot trading processes shall not interfere with ATCOs authority to make tactical decisions to ensure safe operations.

and is included in the IFATCA Technical and Professional Manual.


SESAR Detailed Operational Description.

‘The design of a market mechanism to allocate Air Traffic Flow Management slots’, L. Castelli, R. Pesenti, A. Ranieri, 2011.

SESAR Concept of Operations Step 1.

IFATCA Technical and Professional Manual.

Last Update: September 30, 2020  

May 3, 2020   557   Jean-Francois Lepage    2013    

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