The continuing rise of continuous descents

Posted: 11 December 2009 | David McMillan, Director General, EUROCONTROL | No comments yet

Continuous Descent Approaches (CDA) are on the rise: March 2009 marked the launch of the European Joint Industry CDA Action Plan, backed by IATA, CANSO, ACI-EUROPE and EUROCONTROL1. Since then, according to EUROCONTROL’s CDA Implementation Support Team, implementation progress has been non-stop. Why are CDAs gathering this momentum?

Continuous Descent Approaches (CDA) are on the rise: March 2009 marked the launch of the European Joint Industry CDA Action Plan, backed by IATA, CANSO, ACI-EUROPE and EUROCONTROL1. Since then, according to EUROCONTROL’s CDA Implementation Support Team, implementation progress has been non-stop. Why are CDAs gathering this momentum?

Continuous Descent Approaches are an aircraft operating technique which reduces the amount of level flight in an arriving aircraft’s descent; this reduces fuel burn and also has benefits in reducing noise. In fact, it has been calculated that in the European Civil Aviation Conference (ECAC) area, CDA has the potential to save over 150,000 tonnes of fuel per year, the equivalent of almost 500,000 tonnes of CO2. That’s not to mention an estimated one to five decibel reduction in noise impact on the ground per flight2.

The European Joint Industry CDA Action Plan supports the SESAR (Single European Sky ATM Research Programme) requirement for CDA to be in widespread practice by 2013. SESAR aims to deliver greater safety, capacity and environmental sustainability. With such a target, the support of all industry partners is essential in its implementation.

One of the key aims of the Joint Action Plan is to work together so as not only to raise awareness of CDA and its potential benefits, both business and environmental, but to provide active support to stakeholders. This could take the form of collaboration, or expert advice and best practice both before and during implementation, as well as maintaining follow-up contact to monitor progress. Support from EUROCONTROL is provided by the CDA-CIT, a dedicated team of controllers and pilots who can provide expert advice and support as required.

The target of rolling-out CDA to up to 100 ECAC airports by 2013 is a challenging one, but those in the know are surprisingly confident that this target can be met, possibly even exceeded. The key to success is not to look for the so-called big bang approach; in other words, don’t expect to implement CDAs from the top of descent 100% of the time from the outset. It is better, say the experts, to achieve the accomplishable, in a situation where it’s safe and practicable, rather than setting targets that are destined to be broken.

Therefore, the objective is to carry out CDA from whatever flight level at whatever time, such as during quieter traffic periods, rather than trying to force a CDA to the detriment of other considerations, such as capacity. This is the key to establishing a CDA culture, which will allow the technique to flourish at its own pace, as opposed to creating a situation which invites failure by raising unreasonable expectations. As the Action Plan states: ‘CDA is the art of the possible’, and laying the foundations of good practice in the beginning can pave the way to more advanced performance in the future.

Implementing CDA involves three levels of commitment. Firstly, organisations give a commitment to investigate the feasibility of CDA at their airport(s). The next stage is to implement CDA if it is found to be a feasible option. Finally, for those who have passed the first two steps, or those who believe that they are already doing CDA, the logical conclusion is to formalise the process. At present, over 60 airports are committed to levels one, two or three, with seventeen already carrying out an established form of CDA and up to five others expected to confirm by the end of this year that they are compliant.

Leading the way are Warsaw, who have published CDA procedures and are measuring progress; Helsinki; the London airports; Munich and, of course, Stockholm, who have been carrying out Green Approaches at Arlanda Airport since 2006. This is to name but a few of the seventeen who are already operating CDA.

So what exactly does CDA compliance involve? Well, there is only one CDA, but in fact there are various ways of achieving it. The simplest of these is to give the pilot the freedom to use his or her own discretion to follow an optimal flight path. Alternatively it can be achieved through, amongst other things, air traffic controllers’ giving the pilots distance-to-go information on approach – as happens in the London TMA or, like Marseille, where the published STARS contain CDA information.

Also possible is a P-RNAV route with CDA embedded, or a combination of these methods. Techniques and possibilities will vary according to the local situation. However, compliance is judged to have been achieved if the CDA is in accordance with the harmonised framework as laid out in the EUROCONTROL CDA Implementation Guidance manual: to use minimal thrust and avoid level flight to the extent possible within the bounds of safe operations.

Of course, no implementation programme is complete without performance monitoring and reporting, according to agreed indicators, in order to both identify and measure improvements. Organisations implementing CDA are now being asked to measure baselines, for example from radar data or noise monitoring data, so that they can estimate and then measure performance improvements. With CDA, a key indicator is fuel savings as this not only gives a direct indication as to the amount of CO2 reduction but also measures economic benefits too.

With interest from ECAC States and airports ranging from Jersey to Portugal and right out to the Ukraine, it’s expected that next year implementation will move even more swiftly, and declarations of compliance will increase.

The CDA-CIT has recently been approached by Turkey as part of their new Green Airport campaign and an initial visit has been planned. In fact, the level of commitment in certain countries is such that it is possible that, once established at one or two airports, CDA implementation will quickly expand throughout a State.

For interested parties who would like to track progress, EUROCONTROL plans to launch an online interactive map where it will be possible to access a range of CDA-related information. This will be available with varying degrees of access for the general public and stakeholders and will show CDA implementation status throughout Europe. Any airport interested in being featured on the map as a CDA airport should feel free to contact the CDA-CIT to discuss their inclusion.

Naturally, CDA cannot be achieved by one operational stakeholder in isolation: it requires the collaboration of Airport Operators and Air Navigation Service Providers, as well as the airlines. One of the most effective ways of achieving this is by forming an airport environmental partnership through Collaborative Environmental Management (CEM).

However, CEM, also targeted by SESAR for wide-spread implementation by 2013, is not only for the implementation of CDAs: many airport operational teams who have formed such partnerships to facilitate CDA implementation are finding they have created a vital and dynamic forum for the mitigation of other airport environmental problems, such as tackling noise issues or reducing taxi times, and are now looking to formalise this as part of a CEM roll-out programme.

Conversely, airports with collaborative procedures already in place will find that they provide a good working basis for CDA implementation. CEM, as the younger initiative, does not yet have the sustained momentum of CDA. Having said that, its inclusion in the ACI EUROPE and CANSO work programmes makes it likely that the roll-out will gather pace over the coming months. Consequently, EUROCONTROL is developing a suite of tools to assist stakeholders with CEM implementation, such as an online forum and information source for collaboration between various airports, as well as putting together a support team to offer advice on request.

Other techniques requiring multi-stakeholder collaboration, where CEM could facilitate implementation, include continuous climbs and curved approaches. Continuous climbs work on a similar premise to CDA – except in reverse; the theory is that by ascending an aircraft directly to its cruising flight level, avoiding periods of level flight, less thrust is required and therefore less fuel is used and CO2 emissions are reduced. An additional benefit is a reduction in noise impact. Curved approaches do require some specialist equipment and so are not yet an option for widespread implementation. However, Stockholm-Arlanda has recently become the first airport to have the procedure published in a national Aeronautical Information Publication and it is expected to eventually help achieve a significant reduction in noise for communities south of the airport.

For any airport considering the implication of such new techniques, it is important to be able to assess the potential environmental impacts, both beneficial and possibly adverse, as well as any possible trade-offs with other environmental issues such as noise and local air quality. EUROCONTROL is currently developing a tool to assist operational stakeholders to assess the potential environmental implications of making such operational changes. The tool, known as ENVScreen, asks users to input the factors which would be altered by the operational change. It then assesses the potential impact to noise levels, local air quality and CO2 emissions which would be incurred, to provide an overview to aid decision making or as the basis for a more detailed assessment. Currently in the final test phase, it is expected that the tool will be available for use by the end of the year.

Next Steps

Of course, if CDAs are to be used whenever possible, it is essential that those involved have the skills and knowledge required to execute them. On this basis, EUROCONTROL’s training arm, the Institute of Air Navigation Services in Luxembourg, is in the process of developing a short Continuous Descent Approach course, to be offered in addition to the existing Environment in ATM classroom training.

Aimed at both controllers and other operational stakeholders who may be involved in implementing CDA techniques, it should help introduce best practices and give technical guidance, as well as start to build the kind of peer-to-peer interaction and networks which can foster a pan-European CDA culture. This course is expected to be available from mid-2010 and should be run two to three times per year, depending on demand.

In recognition of the potential wide-scale benefits of CDA, ICAO is now in the process of developing international CDA guidelines. Based partly on the EUROCONTROL CDA Implementation Guidance manual, techniques will be standardised at a global level.

Aviation stakeholders are under increasing pressure to cut costs and meet environmental targets. In this context, techniques such as CDA, which can both save fuel costs and cut emissions, not to mention reduce local noise impacts, are a win-win-win. Consequently, momentum is growing and leading to widespread implementation across ECAC and beyond: SESAR targets of up to 100 airports by 2013 look increasingly likely to be met.

It’s important to remember that the key to establishing a CDA culture is to start by implementing what is reasonably possible. This means, at least initially, concentrating on carrying out CDA when the conditions are more amenable, for example in quieter traffic periods, rather than trying to force them 100% of the time right from the start.

CDA is a technique which requires the co-operation of all airport operational stakeholders, and this is driving the formation of collaborative environmental partnerships. Working together is pivotal in the CDA culture: CDA cannot be implemented by a single stakeholder acting alone. As one pilot involved in CDA implementation puts it: “We’re all in this together. There are no pilots, no controllers, no airports: we’re just all CDA professionals.”

To contact CDA-CIT, e-mail [email protected]


  1. International Air Transport Association; Civil Air Navigation Services Organisation; Airports Council International; the European Organisation for the Safety of Air Navigation
  2. Source: European Joint Industry CDA Action Plan
Send this to a friend