One of the first challenges will be to measure performance and define a harmonised definition of a CDO in a meaningful, standardised way across all stakeholders’ groups within acommon set of parameters. Without this, CDO operations are not yet delivering the benefits they could.

“If you measure performance you improve performance,” says Brain. “We want to do it for all European airports and all airlines flying in Europe, subject to data availability, on a monthly basis with the best performing airports and airlines identified. But there are other aspects of performance as well. Some airlines have really good practices and we think these should be followed throughout the industry. However, CDO measurements at some airports are focused only on the last part of the descent operation. A CDO at London/Heathrow, for example, is pretty much standardised to optimise the noise footprint of arriving aircraft from 6,000 feet down to 2,500 feet, when the aircraft intercepts the ILS glideslope. But if you have a descent profile starting from top of descent (e.g. flight level 360) and you are focusing just on the last 3,000 feet or so down to glide slope interception, that is just one-tenth of the whole vertical profile. There are also big fuel savings to be counted if we optimise from top of descent, and this is really where I think it should be focused.”

The main challenge is to overcome the silo approach to adopting more environmentally responsible operations. Aircraft manufacturers do not have specific references to CDOs in their aircraft operating manuals. ANSPs do not always train their controllers to understand the impact of air traffic control (ATC) instructions on pilots and pilots do not always understand why controllers give them the instructions they do.

“Predictability is an important element here,” says Brain. “It sounds like an easy word, but it means different things to pilots and controllers. When pilots say they want predictability, they want to know what’s going to happen to them en-route from the current location to the airport; they don’t know if they are going to be vectored 100 miles out the way or receive instructions to level-off during descent. They need to be told as soon as they are on frequency what’s going to happen and with appropriate information provided so they can plan an optimum descent profile. But from the point of view of controllers, predictability means they want to know what a pilot is likely to do if he or she has been given an instruction. For example, if the controller says “descend flight level 100”, some pilots may do it immediately, others may do it after 10 or 15 seconds, others may use a lower or higher rate of descent. The controllers need to know that all pilots will do the same thing.”

The task force is proposing some updates to controller training material on CCO/CDO and is developing a new controller refresher training module on aircraft energy management so that controllers and pilots can together manage optimum descent profiles even in complex airspace. It will require new levels of collaboration between controllers and pilots.

“We are promoting the work of Collaborative Environmental Management groups, where all operational stakeholders come together at an airport to identify how they can work together to promote environmental benefits, and CDO is one of them,” says Brain. “But more than that, we have seen that projects, for Innovation example in Germany, have been successful because the individual pilots and controllers working on a specific procedure have come together. So, it’s a more generic collaboration initially, followed by a more focused approach by the actual operational actors working in collaboration with each other.”

CDO operations in complex airspace offer a particular challenge, especially when CDOs start in the airspace of one State and finish at an airport in another. The European CCO/ CDO Action Plan will highlight some of the factors that might affect optimised CCO/CDO performance and they include the way airspace is designed and allocated in neighbouring States and air traffic control centres. Cross-border operations are already framed by Letters of Agreement (LoAs) – and cross-border CDOs will require a new, more flexible approach for these agreements.

“If you have a descending aircraft between two different sectors, the agreed transfer of control level between the two sectors may be flight level 320,” says Brain.

The flight level 320 will have been agreed based on the average flight profile of aircraft that cross this boundary, or it might be designed to keep the aircraft out of a neighbouring sector that has capacity issues.