Who has this summer? traveled by plane, most likely had delay on the outbound or return flight. The data of Eurocontrol – an intergovernmental organization that deals with air traffic control – show us that in Europe between June and August 2024 40% of flights were delayed, while about 50% left after the scheduled time. But how is this possible?
the truth is that the management of air traffic is very complex, especially during the summer when the skies are overload and the airspace is saturated. Let’s see what factors are at play that make air traffic so complex and why delays occur, especially in the summer.
Delayed flights: Here’s why 15 minutes changes everything
It’s not just an impression, the data speaks clearly: in Europe, during the summer period, approximately two flights out of five arrive late, while almost one in two leaves after the established time. Official Eurocontrol data says so. But how is it possible?
First of all, in statistics a flight is considered in delay when it leaves (or arrives) at least 15 minutes after the scheduled time. 15 minutes may not seem like much, but in the world of air traffic it makes a huge difference.
In fact, the first concept to know is that of slots, or technically CTOT – Calculated Take-Off Time – that is, the time at which a flight is scheduled to depart. Each slot has a time window of tolebrance Of 15 minutes, that is, in case of necessity a flight is authorized to depart from 5 minutes before to 10 minutes after compared to theexpected departure time. After these 15 minutes, the plane cannot depart “as soon as it’s ready”, but will have to wait for the next available slot, which could be 10 or 20 minutes later, or sometimes even hours later.
The division and management of airspace
But it is not only the departure and arrival that must be considered in the planning, but also the flight phaseThe management of each individual flight is in fact divided into different phases.
Once a flight is assigned a slot and its operation is cleared take off begins the put in motorcycle, that is, the exit from parking and the movement within squares, followed by the taxiing, that is, the positioning on the runway. In this phase, the pilot speaks directly with the control tower (TWR) which guides him out of the parking lot onto the runway and gives the authorization to take off only when a safe distance is guaranteed with all other flights, both near the take-off area and along the route it will take. Once taken off, the aircraft is accompanied by the service approach up to the cruising altitude and course.
The Flight Information Region (FIR) in Italy
And here we come to the crucial part of the flight. Even if the airspace seems immense to us, in truth there is a maximum number of planes that can transit at a certain time and in a certain portion of space. The sky above us is divided into FIR, Flight Information Region: of the volumes, pieces of sky, where each State has the responsibility to provide flight and warning services.
The FIR They are in themselves uncontrolled areas, that is, planes can pass through them freely, but they contain controlled areas and the vast majority of airliners pass through them. Controlled areas along their route, which have different categorizations depending on their proximity to airports but also their size.
In fact, in addition to the airport control towersair traffic controllers are in the Control Centers (ACC) located on the territory. Then above the FIR, that reach up to 19,500 feet altitudethere are the UIRwhich are organized more or less in the same way but are always controlled.
In Italy there are 3 FIR:
- that of Milan, managed by two Control Centers, one in Milan and one in Padua
- that of Rome, managed by the control center in Rome
- that of Toasts, managed by the Brindisi control center
Each ACC manages different sectors, that is, boxes, portions of sky, and each sector is managed by a specific air traffic controller.
Air traffic sectors and controllers
THE sectors they are not all the same, they do not have a fixed sizebut they are different depending on the area and depending on the needs they are merged – for example when there is little air traffic and therefore a controller can manage a larger space – or divided into smaller parts when there is particularly heavy traffic.
In the maximum configuration, that is when all sectors are open, in Italy if they count 68: 6 Brindisi, 21 Milan, 14 Padua and 27 Rome. But often they are not all open at the same time: for example the ACC area of Rome can end up being grouped into just 4 main sectors, for example at night when traffic is much less.
Well, you have to imagine a huge three-dimensional grid which divides our sky into boxes, that is, sectors, and each of these boxes is managed by a specific controller of air traffic.
To ensure that the controller of a certain sector is able to correctly conduct each individual flight safely, it is necessary to impose a certain hourly capacitybut also space. In fact, even in heaven there is the safety distancesaid separation, which is 1,000 feet, or approximately 300 meters, vertically and 5 nautical miles, that is approximately 9.5 km, horizontal.
So when a delayed flight is due to depart, not only do you have to find the correct departure and arrival slots, but you also have to consider everything that happens in the flight.
Reasons for delays: bad weather, capacity and staffing
In summer the skies are overload and air traffic increases. And when even a single sector of airspace becomes saturated, the systems reassign aircraft slots so as not to exceed the hourly capacity of the sector.
And this reorganization of the slot it is not anomalous or exceptional, quite the opposite. Think for example of the bad weather: inevitably the planes remain in the air longer, therefore they occupy the sectors for longer delaying all the flights that will have to pass through them after them. Or again due to bad weather some sectors are closed. Then there are portions of the sky where it is not possible to pass, such as war zones, in the case of Europe for example, Ukraine.
According to Eurocontrol data, another very relevant factor is that of staffing, that is, the staff. In 2020 and 2021, the technical staff – that is, controllers and workers – was significantly reduced due to the lack of air traffic.
And now that the crisis is over, the number of flights has returned to 2019 levels, but not the number of controllers And qualified technicians. We must in fact consider that these are highly specialized jobs, for example at least a year of training is needed to become a controller.
When there are not enough controllers to manage all the sectors, it happens that the sectors are merged, so that the airspace can be managed by fewer controllers. However, this means reduce hourly capacitythat is, fewer flights can pass through.
The same thing can happen to the staffing from the airlines: We have often heard of cases of flights being cancelled due to lack of staff or strikes.
