Eurocontrol: Making the connection: the First Rotation Hours Optimisation Trial

The issue

As the main hub carrier at Zurich Airport, SWISS operates both short- and long-haul flights to offer attractive connections for its transfer passengers. When the airport's capacity is constrained, the Network Manager Operations Centre (NMOC), in collaboration with skyguide, the Swiss air navigation service provider, normally assigns air traffic flow management (ATFM) restrictions for inbound flights, following specific attribution rules.

The problem here is that the NMOC has no information about either the airline's commercial schedule or the number of transfer passengers who will be affected by a restriction on a particular flight. Only SWISS has an idea of the number of possible passenger misconnections that an ATFM restriction might entail.

The result is all too often very short connecting times for passengers. This could be avoided if the impact on transfer passengers had been taken into account in the regulation assignment process.

Besides, a delay will also affect an aircraft's connecting time to its next planned sector. Since an aircraft is normally scheduled to operate several flights in a row, its daily schedule will be particularly challenged by any ATFM restrictions that are imposed early in the day, during the so-called 'first rotation hours'.

In contrast, ATFM restrictions imposed late in the afternoon cause less reactionary disturbance, as the same aircraft will have fewer flights left to carry out before the night movement ban. In either case, however, given that any deviation from the plan normally leads to a higher degree of complexity for transferring passengers, it is vital that planned aircraft schedules are followed as closely as possible.

Addressing the matter

SWISS and EUROCONTROL's Network Manager (NMOC, the Central Office for Delay Analysis (CODA) and the Airport Unit) in collaboration with skyguide and Zurich Airport, are currently trialling a new concept known as the First Rotation Hours Optimisation Trial, which addresses recurring ATFM arrival restrictions in Zurich.

For several years now, skyguide has been applying arrival restrictions in Zurich on the third wave of arriving flights (from 10:40 to 13:15 LT), practically every day. This gives calculated take-off time or CTOT assignments for almost all SWISS flights inbound to Zurich in this period.

However, when favourable meteorological conditions prevail, a substantial number of these flights are normally subject to on-time slots and, as a result, arrive on time. The First Rotation Hours Optimisation Trial was launched on the basis of this finding to develop a procedure that helps to minimise the numbers of misconnections, also on days with unfavourable conditions.

The trial

The First Rotation Hours Optimisation Trial concept works as follows: each day, SWISS's Operations Control Centre (OCC) is invited to select two flights that are scheduled to arrive when the Wave Three restrictions are in force. The two flight numbers must be communicated by 06:30 LT to the NMOC, which then allocates on-time slots to them. This means that SWISS can expect the selected flights to land in Zurich on schedule, and their connecting passengers will be almost certain to catch their onward flights.

In return, SWISS ensures that all its flight plans are kept closely up-to-date, and that these also reflect any departure delays in the second outbound wave at Zurich Airport (from 08:00 to 10:00). This results in improved demand prediction stability - and leads in turn to more flights' operating punctually, so reducing reactionary delays.

The results so far

The First Rotation Hours Optimisation Trial has been applied daily in Zurich since 18 July 2017. After 211 SWISS-selected trial flights:

• 76% departed in accordance with their initially-allocated CTOT, arriving in Zurich on schedule;
• 24% departed outside their initially-allocated CTOT window for operational or technical reasons (mostly slot revisions owing to late arrival, last-minute loading, boarding etc.);
• 99.12% of the transfer passengers from the selected trial flights were able to board their connecting flight on time thus helping reduce delays for Wave Three departures;
• the flights of other airlines were not affected negatively by the trial procedure, since the trade-off between prioritised and non-prioritised flights was only done with suitable SWISS flights.

On the strength of this positive outcome, all partners decided to extend the trial period to the end of March 2019. Their shared objective is to implement the First Rotation Hours Optimisation Trial concept as a local standard procedure at Zurich Airport, provided these initial findings can be confirmed.

What next?

SWISS is convinced that user-driven prioritisation (UDP) processes are beneficial to all ATM stakeholders, and that they are an important prerequisite for enhancing operational control. The company now aims to develop the concept further and prioritise up to four flights a day.

Given the current situation at Zurich Airport, however, and the fact that prioritising one flight always requires a trade-off with another flight by the same company, group or alliance, some difficulties have yet to be overcome. In view of this, a slot-swapping tool is being developed to manage the third wave proactively.

Other airports and airlines have already shown interest in the First Rotation Hours Optimisation Trial concept, and have asked SWISS and the Network Manager to assist in adapting it to their local conditions. This clearly illustrates the need for more and improved collaborative decision-making processes when managing the ATM system's capacity restrictions.

The First Rotation Hours Optimisation Trial and other UDP processes can only be carried out, however, when all the operational staff involved are totally committed to the process. Indeed, initiatives like this one are ultimately for the benefit of the most important stakeholders of all: our passengers!

The verdict

"Swiss International Air Lines' efforts to keep flight plans up-to-date improved the arrival demand picture at Zurich Airport during the trial. This contributed to a positive network impact with fewer ATFM arrival delays due to airport capacity,"said Daniele Gentili, Deputy Operations Manager, Network Manager, EUROCONTROL

"Thanks to this new process, which proactively manages our third arrival wave in Zurich, we are able to optimise the arrival sequence at our home base and so run smoother operations. This project shows our strong collaboration with EUROCONTROL and our shared commitment to improving ATM in the European sky," said Jan-Christian Schraven, Head of Continuous Improvement, Swiss International Air Lines