Most of the airports that SWISS currently flies to, especially within Europe, are congested either at peak times or throughout the entire day. This congestion can be caused by a number of factors, any of which can be the critical factor. Because of this congestion, airports are bracketed into 3 distinct groups by IATA, using criteria that are accepted worldwide as the standard.
The groups reflect the level of congestion at the airport, ranging from no congestion at all, congestion during certain periods of the day, or congested throughout the day. This congestion can be caused by a number of factors, with these factors impacting each airport differently. For instance runway or apron availability can affect some airports, airspace above or around the airport at others, whilst lack of check-in counters or security checkpoints can affect others.
For airports where congestion is experienced, access is limited by airport slots which are issued to carriers to determine the timings that they can operate flights at. These airport slots are granted to enable a flight to operate at a specific time of the day taking into account the availability of all necessary infrastructure at the airport. This slot can then be extended, for example, to the same timings, every day of the week for the whole of the scheduling season, or every Friday between June and September, or as required for each individual flight.
These slots are also capable of being obtained on a Historical basis, whereby the airline is entitled to operat the same slots in the winter or summer scheduling period for successive seasons if certain requirements are met. This entails the carrier operating a certain percentage of the flights that it planned within the period, whilst also ensuring that the flights flown were also punctual within recognized tolerances.
About 9 months prior to season start, Network will request slots for all the planned flights for the upcoming season. These slots will include the Historical slots gained from the previous season’s operation, plus any additional ones necessary for new or amended flights, or for any slots that were lost due to unpunctual or cancelled flights. These slots may not always match our requirements and therefore negotiations take place to try and achieve the best possible timings for the flights. This process can go on right up until the day before the flight, although normally they will be determined at least 6 weeks before departure due to crew and passenger notification issues. We also monitor the flights throughout the season to keep track of the punctuality to ensure historic precedence can be assured and also avoid any possible sanctions due to unpunctual services.