Air transport around the world, and particularly in Europe, experienced major capacity, efficiency and environmental challenges to improve performance. The Airborne Separation Assistance System (ASAS) uses ADS-B (Automatic Dependent Surveillance-Broadcast) data to provide improved airborne surveillance in support of new procedures for controllers and pilots.
ASSTAR addressed these issues by researching and validating two areas of ASAS Package II functionality, which are expected to provide significant benefits in terms of operational and environmental improvements in the short-term.
The objective of ASSTAR was to perform research into the operational and safety aspects underlying the introduction of the following two key ASAS Package II applications with the aim of realising the significant potential benefit to the user community in the 2010-plus time frame:
- The delegation of conflict resolution manoeuvres to the air, in radar controlled airspace (i.e. ASAS crossing and passing), in order to reduce controller workload and improve flight efficiency.
- The use of ADS-B to support new operations in oceanic and other non-radar airspace, enabling more optimal routing, including enhanced use of wind corridors and passing and level changing, that are currently severely restricted due to the procedural separation standards.
The outcome of the ASSTAR project is a number of well-defined ASAS applications covering both the radar and non-radar themes, including: ASEP-C&P Airborne separation crossing & passing, ASEP-ITF Airborne separation in-trail-follow, ASEP-ITM Airborne separation in-trail merge, ASEP-ITP Airborne separation in-trail procedure and ASAS-FFT Self-Separation Free Flight Track.
The project establishes the viability of these applications with respect to the following:
Definition of operational concepts and scenarios
- For each of the two themes, the operational concepts and scenarios are identified, analysed and defined
ASAS manoeuvre design and execution
- The design of the applications involves the definition of the functional logic and algorithms.
Operational procedures and training requirement
- The procedures are specified, refined and then reviewed by controllers and pilots.
Ease of installation and implementation
- The air and ground infrastructure is investigated, for both radar and non-radar scenarios, with respect to the changes required to the current equipment and tool sets, the intention is to minimise the amount of changes to existing hardware and software. This activity encompasses elements of installation, certification and validation.
- Preparation of a benefits analysis, particularly in terms of the end users' business case
- Provision of feedback on applications from the safety perspective, with respect to hardware, software, human factors, environment and the interaction of these various aspects.
The project investigated the implications of five applications and their impacts as regards benefits/disadvantages in comparison with current operations, finding that:
- For C&P, the main focus of operational benefits resides in the ATCO workload reduction while the aircraft can fly a more efficient route even in a conflict resolution path. Without real-time simulations, it is not possible to precisely assess the effect on flight crew workload.
- For ITP, the main operational benefits are related to aircraft efficiency, while no impact is readily apparent for ATC.
- For ITF, in addition to aircraft efficiency, some benefits to ATM efficiency are possible due to enhanced usage of available flight levels as well as improved traffic flow management.
- For ITM, ATM and aircraft efficiency are increased compensating the probable increase in ATCO workload.
- For FFT, the benefits brought by the addition of one Free-Flight-Track affect both the ATM and the aircraft efficiency, while reducing the ATCO workload. The increase in flight crew workload is based on the results of real time simulations.
It is important to note that the significance of the operational benefits can vary depending on each stakeholder. For instance, NATS and DSNA, as ANSPs, were interested in investigating the potential reduction in ATCO workload. The absence of an airline in the consortium did not enable a detailed assessment of benefits from an airline perspective.
Measurements show that ITP applications do not provide a flight time reduction but ITF and FFT provide average flight time reductions which are a number of seconds rather than a number of minutes. A reduction of less than a minute of flight time will not provide a meaningful benefit to an aircraft which is scheduled to undertake two oceanic crossings a day. In practice it is thought unlikely that a particular aircraft or aircraft type will consistently experience a significant flight time reduction benefit.
The reduction in fuel consumption which arises from improved flight efficiency can lead to direct cost savings and reduced environmental impact and these range from 150Kg for a single oceanic crossing for ITP to 220Kg for ITF and FFT, resulting in a reduction in CO2 emission of no more than 0.9%.
A cost benefit analysis has determined that for the retrofit of FFT the net present value is €390,000 per aircraft to an airspace user based upon an 8% discount rate. This co
ASSTAR made five recommendations for work requiring further technical evaluation and development:
- Airborne separation minima. Safety studies need to be conducted to confirm that the chosen separation values are always above airborne separation minima for each application investigated. In the particular case of ASEP application in radar airspace, it is recommended to ensure that the airborne separation values are the same as ground separation minima in order to help the ATCO to resume responsibility at the end of the procedure and even in case of abortion of ASEP procedure.
- Airborne systems. ASSTAR studied the possible functions and architectures needed to achieve one specific application. Verification is needed that one single system is able to support all airborne separation applications. The navigation data (position and velocity) of all traffic are critical to ASEP or SSEP applications and it is necessary to pursue activities on the integrity and continuity of navigation positions for all traffic of interest, and conduct studies on the robustness of the broadcast data link to ensure it can support the selected applications.
- Flight deck. It is recommended to undertake proper assessment of flight crew workload and their acceptability of new procedures in association with the level of automation provided by the ASAS functions.
- Combination of ASEP applications. During the course of the project, it has been found that new applications or scenarios were found worth considering, and indeed most oceanic applications should not be seen in isolation, and RTS performed on oceanic operations as well as ASSTAR scenarios favour a combination of applications.
- Conflict involving more than one aircraft. Work on oceanic procedures has revealed that in addition to ITF or ITM investigation of new scenarios were beneficial. These scenarios need to refer to a conflict with three aircraft with one of the three ensuring separation simultaneously towards the two others. This broadening approach is also useful for a transition to self-separation where multiple aircraft surveillance, conflict detection and conflict resolution is required.
ASSTAR has directly addressed one the recommendations of the SESAR project, that 'When such cooperative separation or self-separation applications are implemented, a clear and unambiguous statement for separation responsibility is required.' ASSTAR work on the operational procedures surrounding this concept provides valuable information in the definition of phases for the management of airborne separation. In addition, draft amendments were proposed in D4.3 and D6.3 for inclusion in PANS-ATM and PANS-OPS to support global interoperability as well as international standardisation, and has suggested benefits which should be further substantiated by further research, namely:
- That the delegation of separation responsibility may reduce controller task load and increase safety, and
- That significant capacity gains can be achieved.
One difficulty encountered in cost/benefit assessment is the requirement from the SESAR community that the operational benefits should be provided to the ASAS-equipped aircraft rather than all the traffic. The difficulty arises from the fact that in a conflict where ASAS separation is used, only the equipped aircraft is able to monitor the resolution of the conflict and is likely to manoeuvre, whereas the non-ASAS equipped cannot manoeuvre without ATCO instruction. It is thought that airborne monitoring alone may enable a significant proportion of resolutions that ATC might otherwise have solved by manoeuvring one or both aircraft in conflict.