If you fly with any frequency, you may well have heard a pilot say the phrase — especially in relation to a sudden delay — “we’ve lost our landing slot.”
So what exactly does this magic word slot mean? Well, on one level it refers to the interval of time allotted to an aircraft to execute a determined operation or maneuver, such as permission to take off or land. But this is a longstanding aviation term which has a number of different meanings, and there are different types:
Airport slots are the ones that passengers are likely most familiar with, the intervals that constitute administration authorisation entering or exiting an airport during a stipulated time frame. This is the period in which we can take advantage of each airport’s infrastructure and services: fingers, check-in counters, parking, and so forth. These are always administered and granted by the airport authority — in the case of Spain, an outfit called AENA. Here’s an example of how they work. At a given airport, various carriers would like to be able to depart at 8am for reasons of profitability or convenience of connections, but as much as the local airport authority would like to satisfy all of them, only half the number of departure gates are available to meet the demand. So allocation is determined by a tariff system; it doesn’t cost an airline the same to depart at 9 a.m. using a jetway, as to depart at 4 a.m. using a runway shuttle bus.
Aeronautical slots (aka takeoff slots) in Europe depend on the European Organisation for the Safety of Air Navigation (EUROCONTROL) in Brussels, which manages the continent’s airspace to prevent air-traffic mishaps. The aeronautical slot is basically your flight’s takeoff time allotted by Eurocontrol, based on congestion, air traffic, weather, and other relevant factors. In some cases it’s possible to request an extension of the slot, particularly if the pilot believes he or she will be unable to have the aircraft ready to depart within the time initially allotted, and if Eurocontrol authorises such an extension, a new slot will not need to be assigned. Occasionally a pilot may make a cabin announcement to passengers along the lines of, “ladies and gentlemen, unfortunately we’ve lost our slot, we’re going to need to request a new one,” initiating a tarmac wait of a few minutes or longer.
Historical slots are positions that have been earned as a legacy of years of activity at a given airport — but in order to hang on to them, an airline must maintain a certain percentage of flights as agreed with the airport management authority.
This is another reason why flights have to be closed 45 minutes before departure, why boarding is generally started from the back rows first, and why carriers always do their best to save as much time as possible during each stage of their operational day. Delays are not good for either companies or their passengers, and furthermore they often can have ripple effects on an entire day’s scheduled flights.
For just a little more on the subject of slots, check out this video (don’t forget to click on the English subtitles!):