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With ever increasing demand in air travel, most airports around the world are slot constrained. The International Air Transport Association (IATA) categorise airports in terms of congestion, applying a system with Levels 1, 2 or 3, depending upon a number of factors such as capacity of the airport infrastructure (runways, taxiways, gates, etc.) or government- imposed conditions, either of which limits the airport’s capability to meet traffic demand.4 The process of slot allocation requires airlines to have a slot allocated by a coordinator in order to arrive and depart at the airport when slot allocation is active. Not only may the creation of schedules be governed by slot allocations, but day-to-day operations may also be affected by normal and non-normal influences. The IOC matches the COBT or EOBT (calculated or estimated off-blocks time) with slot allocation to ensure any discrepancy does not exceed a permitted allowance (e.g., plus 15 minutes or minus 5 minutes), aware that non-compliance may result in some penalty - typically additional airborne holding time. If otherwise delayed flights miss their allocated slot times, then renegotiation of the slot(s) if this is possible, or having to await the next available slot, may result in considerable disruption to the network. Should an arrival slot be extended, the flight may then be subject to further flight time, implying additional fuel burn, increased crew hours, and potential threat to onward connections and aircraft turnaround time at the destination. Of course, gate parking, ground resources, and reduced turnaround time of the aircraft may also be consequential effects.

Noise Abatement

Procedures determining the departure or arrival tracks of aircraft are used to mitigate the effects of noise over sensitive residential or other community areas. These procedures provide for adherence to specific flight paths and power settings, with nominated heights for manoeuvres such as circling, or conducting approaches into, or departures out of, an airport. They also provide for using nominated or preferred runways (e.g., utilising a specific runway for arriving and departing aircraft), and the use or limitation of applying reverse thrust on arrival, especially for operations conducted inside the curfew period (with due dispensation).

Airport Characteristics

Airports vary enormously in terms of their geographical location, altitude, environmental surrounds, physical layout, numbers and configuration of runways and taxiways, apron design, parking facilities, fuelling points, and other passenger and freight areas. Some of these characteristics result in considerable performance limitations affecting aircraft taking off. For example, the high-density altitude of Denver International Airport, USA (5,400 ft above sea level) can limit aircraft take-off performance, which may reduce the uplift of payload or fuel, despite the airport’s very long runways. In the centre of Australia, Alice Springs experiences very high temperatures during the Australian summer-time (e.g., 40+ degrees Celsius), resulting in significant payload limitations, or sometimes the need for a technical stop to uplift fuel. Other airports may be located in a valley, on a plateau or side of a hill with subsequent restrictions in operating in or out. Locations such as these are often characterised by difficult weather conditions (e.g., cross-winds, turbulence, wind shear) which may affect aircraft approaches and landings in particular. Other airports (such as Queenstown in New Zealand, Juneau in Alaska) may be surrounded by terrain features that necessitate very precise navigational approaches (e.g., RNP), for which aircraft must have suitable navigational equipment and pilots who are specifically trained.

Pavement Concessions

Some airports have pavement strength limitations with regard to the maximum weight of aircraft that can operate into or out of the airport or park on available aprons. Sometimes, these limitations may allow higher weight aircraft to operate through the airport but curtail the number of movements over a certain time period applicable to some maximum weight. For example, a concession may be approved for a weight of, say, 80,000 kg, but limited to one such operation per week, or a maximum of six per month.


Prior to commencing the operating day, all scheduled flights should ideally be crewed appropriately. To off-set expected crew sickness on the day of operation, appropriate reserve coverage is scheduled at selected airports. Importantly, the expectation by the airline is that all rostered crew members should be adequately rested and fit for duty as well. A further requirement is that they are not under the influence of illicit substances or alcohol and meet all regulatory requirements accordingly. Due to crew training requirements there may be additional crew members on flights. This could be additional Flight Attendants in the cabin who may be under training or may be overseeing trainees or conducting an airline audit on all crew activities during a flight. In the cockpit, a check and training Captain may be overseeing other crew members.

Maximum duty periods including sign-on and sign-off times are prescribed by both the regulator and the airline. In the case of scheduled long-haul flights over, say 12 hours, an augmented (sometimes called ‘heavy’) crew needs to be rostered for the flight to limit the amount of time the crews spend at the controls. This additional crew complement enables up to 20 hours of duty time (subject to airline work agreements). Future longer haul flights (requiring more than 20 hours crew duty time), will need dispensation. The augmented crew composition then, in addition to the ‘normal’ crew of Captain and First Officer, may consist of another Captain, or another First or Second Officer, or a Captain and First Officer; the latter providing for two complete crews. During these long-haul flights, the crews will take turns to have rest period(s) in the dedicated crew rest area.

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