Continuous climb and descent operations

Towards a flexible, optimum flight path that delivers major environmental and economic benefits.

Status of Task Force work flows following the TF#5 meeting (June 2019)

The 5th meeting of the European CCO / CDO TF took place at EUROCONTROL HQ on the 17-18th June 2019. A short summary of the status of ongoing work / outputs of the TF are detailed below. For more detailed notes, please see the following additional pages. All actions, agenda items and participants may be found in appendices 1, 2 and 3 respectively.

CCO / CDO Action Plan Update – The update to the CCO / CDO Action is on track. An updated version has been created based on the comments received since the last TF meeting. The proposed structure will include a one page of key messages (an executive summary), a short (10 page) Action Plan or report designed to be a glossy handout and these two documents will be supported by the State of Play (SoP) Report as an appendix. On the website, these documents will be downloadable as a set or separately. Specific text proposals will be addressed to TF members who made comments in the latest version with an updated draft to be made by the end of August. During the summer, a review of the structure will take place to ensure that all text in the key messages, Action Plan, SoP report and other deliverables is aligned as part of the toolkit to implement / optimise CDO. Based on a suggestion at TF#4 for a checklist of actions for stakeholders to demonstrate their implementation of CCO / CDO, a proposal was made which was met with mixed reactions.

CCO / CDO State of Play (SoP) report – The SoP report has undergone another review since TF#4 and contains much new and reviewed content. This version included updates to section 2 (contributory factors - new content in 2.15 (weather) and 2.16 (interdependencies / conclusions)), section 3 (Stakeholders and the sharing of responsibilities) Section 4 (best practices - new section 4.6 (noise optimisation)) and section 7 (use cases – new example from ENAV). Additional new content was identified. The TF members are asked to provide feedback on the current version (shared 14 June) with a request to focus on sections 2 and 3. Based on comments and requested additional input, a new version will be shared by the end of August. During the summer, a review of the structure will take place to ensure that all text in the key messages, Action Plan, SoP report and other deliverables is aligned as part of the toolkit to implement / optimise CDO. Expect a detailed review of the SoP report at TF#6.

AIP CDO best practice analysis – Following the last TF meeting, a first proposal had been shared on a draft AIP structure and text proposal which had received many comments in a very useful exercise. It was clarified that the idea was to have a harmonised structure and location of content and that the content would be based on local practices at each airport and NOT relate to content that was not applicable at an individual airport. Clear messages were identified. Identifying which sections of the AIP are reviewed by the CFSPs for transposition into the AOMs is not a straightforward process. A request will be made to APDSG at their September meeting to support the TF with the harmonised AIP structure and content proposal.

The next step will be an updated proposal, taking into account the comments provided and will include a proposal for an updated harmonised structure, using identified existing AIP content as bullet points. Once discussions have commenced with APDSG, additional harmonised content can be proposed.

CCO / CDO Performance tables – The proposed performance tables for monthly performance figures on CCO / CDO based on the TF agreed definitions are gathering ever more attention. TF members understand that the monitoring and measuring of CCO / CDO performance is probably the single most important factor for highlighting performance differential and getting stakeholders on board to enable a performance improvement. The basic performance tables are still on-track for the end of 2019. A test data set was shared and the key now is to identify the best graphs / charts for display.

ATCO refresher training – Since TF#4, a baseline structure has been developed that takes into account all the topics that were identified by the TF for incorporation in the refresher training. In addition, the first draft content has been created and shared with IANS who have provided further comments. The next steps will be to identify questions / scenarios of ATCO / Pilot interactions that can be discussed on camera and included in the training material. For example, what do pilots think ATCOs should be informed about that will optimise CDO; and what scenarios would engage the ATCO that convinces him / her to support more CDO. There may be a possibility to film scenarios in the Easyjet simulator. Filming will take place during the September TF meeting with appropriate time to be set aside for filming. The filming may include specific segments with pilots, ATCOs, group discussion or specific contextual content e.g. CDO benefits etc. The TF training sub-group will discuss scenario proposals and identify filming participants prior to the September meeting.

Airline CDO questionnaire – The results of the airline CCO / CDO best practice questionnaire were shared. The questionnaire received an excellent response from airlines with >120 responses from 59 airlines. The results were not as expected – fuel savings / performance improvements from CDO are not a major focus of the airlines and the TF needs to engage and collaborate with the airlines to share best practices that will enable more optimised CDO. Whilst the TF is spoiled with pilot / airline experts on CDO, they are atypical of the airline industry. Detailed results of the questionnaire will be shared with the airline and pilot associations. It is clear that the LCCs are taking the lead in CDO best practices and CDO performance measurement. Responses from the questions related to refresher training will be incorporated into the proposals for ATCO refresher training. The TF sees the results of the questionnaire as THE chance to engage with the airlines. The TF will now aim to make a more concentrated effort to collaborate with the airline Organisations and propose what the TF considers to be best practices on CCO / CDO for the issues covered in the questionnaire. A section will be added to the CDO Action Plan / SoP on best practice guidance for airlines on CDO such as similar proposals for the ATCO training material.

ERNIP Plan update – The proposal for updating the ERNIP Plan is still on course.  All comments will be incorporated into one version to be shared to the TF for review prior to submission to RNDSG for approval. Since TF#4, a set of best practice principles for airspace / procedure design has been developed based upon those identified in SESAR and other studies. These have been submitted to airspace / procedure design experts for comments. The most relevant of these principles will be added to the proposed ERNIP update.

Trajectory downlink data – Presentations were received from surveillance experts on Mode S and ADS-C. The possibility of the downlinking of ToD data depends not just on manufacturer but on aircraft type. Connecting the Mode S transponder to another interface would not be a priority for Airbus especially as it would come as a duplication of the 4D solution pushed through SESAR. ToD information is not available on an interface for the majority of aircraft and it would require a long, technical and resource-intensive process to develop the necessary standards to move this forward. Therefore, it would make sense to concentrate on other surveillance (or telecommunication) data sources e.g. ADS-C, where some messages are already standardised and trials continue. There is still a need to understand how the logic of different FMSs reacts to different (sets of) vertical constraints. The downlinking of predicted trajectories via ADS-C and the measurement of arrival performance by the energy circle are very sophisticated and should be followed by the TF. However, at this point in time, the TF has to ensure that the basics are understood and adhered to: Pilot / ATCO communication / understanding and R/T.

Informative Presentations – In addition to the ongoing work streams of the TF, the meeting welcomed informative presentations from the PRU (Reference Trajectory), Mode S – downlink of FMS parameters (EUROCONTROL), SESAR updates on ADS-C prediction parameters (EUROCONTROL), Energy Circle (Wizzair), HTO from the pilot perspective (Condor and Lufthansa), best practice airport performance measurements (Heathrow) and low noise metrics and dashboard (NATS).

CCO / CDO TF meeting #6 - The next meeting will take place on the 16-17th September 2019 at EUROCONTROL. At the next meeting, the TF expects to focus on maturing the versions of the TF key deliverables (CCO / CDO Action Plan and SoP document), take more time to undertake filming on specific scenarios for the ATCO refresher training and address proposals for CCO / CDO best practices with which the TF can collaborate with the airspace users. Presentations are also expected from SESAR on the Airspace Architecture Study and other CCO / CDO enabling Projects, How FMS logic can enable optimised CDO (Airbus) and the CFSP (Computer Flight Plan Software provider) role in optimising CDO.

Continuous Climb and Descent Operations (CCOs and CDOs) are aircraft operating techniques enabled by airspace design, instrument procedure design and facilitated by air traffic control (ATC). CCO and CDO allow aircraft to follow a flexible, optimum flight path that delivers major environmental and economic benefits - reduced fuel burn, gaseous emissions, noise and fuel costs - without any adverse effect on safety.

CCO and CDO operations allow arriving or departing aircraft to descend or climb continuously, to the greatest extent possible. Aircraft applying CCO employ optimum climb engine thrust and climb speeds until reaching their cruising levels. With CDO, aircraft employ minimum engine thrust, ideally from top of descent and in a low drag configuration, prior to the final approach fix. Employment of these techniques reduces intermediate level-offs and results in time being spent at more fuel-efficient higher cruising levels, hence significantly reducing fuel burn and lowering emissions and fuel costs (see ICAO Doc 9993 and ICAO Doc 9931).

340,000 tonnes

fuel savings (1 million+ tonnes CO2)

150 +


1-5 dB

noise reduction

Implementation support

We, at EUROCONTROL, support CCO and CDO deployment. A dedicated team works with stakeholders (ANSPs, aircraft manufacturers and aviation industry associations such as IATA, A4E, AIRE, EBAA, ERA, ACI and CANSO) to measure and maximise the benefits achievable in the current ATM framework. The team also supports the facilitation of a more advanced CCO and CDO concept that will result from deploying future ATM tools and procedures. A guide to implementing continuous descent is available. 


Deployment of optimised CCO and CDO throughout Europe will be beneficial to all European ATM system stakeholders and will help the network to address the environmental challenges it faces.

In 2018, EUROCONTROL conducted an ECAC-wide CCO and CDO analysis using 2017 traffic data, in order to estimate the potential network benefits of optimising the CCO and CDO in terms of fuel savings, emissions reduction and fuel costs.

 For CCO, the study concluded that 94% of flights in ECAC currently fly CCO to FL (Flight Level) 100 while 74% fly a full CCO to Top of Climb (ToC).

 For those flights currently flying non-CCO profiles, the average time in level flight to the ToC was 168 seconds with per-flight savings estimated at 15kg fuel/48kg CO2/7EUR. Across the network, this would result in a potential average per-departure saving of 4.3kg fuel/13.7kg CO2/~2€

 For CDO, the study concluded that 41% of flights fly CDO from FL75 (the top of the noise CDO) while only 24% fly a CDO from Top of Descent (ToD – the top of the fuel CDO). 

For those flights currently flying non-CDO profiles, the average time in level flight from the ToD was 217 seconds, with per-flight savings estimated at 46kg fuel/145kg CO2/20EUR. Across the network, this would result in a potential average per-arrival saving of 35kg fuel/110kg CO2/15€.

 The ECAC-wide study identified two main conclusions:

  • The results indicate that in Europe the potential savings from optimising CCO and CDO are up to 340,000 tonnes fuel/year, (1.1M tonnes CO2/150M EUR) *; 
  • The potential fuel saving benefits from CDO are in the region of x10 those from CCO.

(*) It should be noted that the achievement of 100% CCO and CDO across the European network may not be possible for a number of reasons, such as safety (i.e. the need to keep aircraft separated by a certain distance or time), weather, capacity or ATCO workload, all of which may be considered as interdependencies, while small inefficiencies in the system are required to operate a flexible and operationally efficient network.

What are Continuous Climb and Descent Operations (CCO and CDO)?

What can air travel industry do to reduce noise pollution?

The European CCO and CDO Task Force

Historically in Europe, the implementation of CCO and CDO operations has been encouraged on an ‘as-much-as-you-can’ basis while, until recently, there has been no harmonised definition of what actually constitutes a CCO or CDO operation. 
In addition, there has been no assessment of the potential network-wide benefits that could be realised by optimal CCO and CDO operations.

In 2015, a task force of European ATM stakeholders was created with the objective of agreeing harmonised definitions, metrics and parameters to measure CCO and CDO operations in Europe. The resulting harmonised definitions, metrics and parameters agreed by the Task Force are recommended to be used by any European ATM stakeholder for the measurement of CCO, CDO or vertical flight efficiency performance in order to enable harmonisation at international level.

The work of the Task Force is ongoing and is expected to be completed by 2019 with the delivery of an updated CDO Action Plan document and a “State of Play’ document on CCO/CDO. 
More information will be detailed on the website once it becomes available.