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Operational Factors

Air Navigation

Airlines are continuously striving for greater economy and efficiency in the way in which business is done. Advances in technology within Air Navigation Service Providers (ANSPs) and in the various ground and satellite navigation systems have improved navigation procedures enabling, for example, reductions in vertical separation, continuous descents into airports (rather than step descents), sophisticated means of flight tracking (such as ‘flextracks’), performance-based navigation, and enhanced systems of air traffic flow. Capitalising on these technologies, properly equipped aircraft and trained crews are increasingly able to optimise their flight paths, leading to savings in time and fuel burn. Each of these deserves considerable discussion elsewhere, but the point here is that the growing use of these evolving procedures and systems has beneficial effects on the operation of the airline and therefore is of great interest for IOCs.


In many countries, airspace is divided into areas determining civil and military use. Regular public transport (RPT) operations are usually unable to traverse military areas or may need special clearances to do so. In time of conflict, restrictions are often in place either limiting or preventing the overflight of dangerous regions. The effects of restrictions such as these are pronounced for airlines. Flight planning around areas of potential or current conflict is necessary, with the result that additional flight time, extra fuel burn and extended crew duty hours will add to the cost of the operation, and also extend the arrival time at the destination with consequential connection and turnaround time considerations. In some severe cases, flights may need to be cancelled until the conflict is resolved or is deemed safe. Another consequence may derive from recurrent late arrivals at a destination. If the particular destination airport operates to a slot system (which applies to most major airports now), and a scheduled flight continually fails to meet the scheduled arrival slot above an allowed percentage margin, the slot time may be taken away from the airline. In the case of losing Grandfather rights, for example, such a loss would be devastating for an airline. A threat such as this is likely to prompt the IOC into investigating solutions to prevent multiple occurrences.


Many airports around the world have legislated curfews in place. These are artificial limitations, in response to community, pressure group and environmental concerns surrounding noise and other pollutants. Curfews relate to RPT operations, and generally not to military, medical or emergency flights. Typically, curfews apply to jet aircraft above a certain gross weight (e.g., 34,000 kg/75,000 lb), whereas other ‘low noise’ aircraft (e.g., some approved jets, smaller jets and turboprops) are able to operate during curfew hours, but often are subject to capped movement numbers.

There may be further concessions for particular flights (e.g., international) which operate under a ‘Grandfather’ clause (i.e., long- established rules continuing to be applied), meaning that some flights (large aircraft) may operate within the curfew period. Curfews predominantly operate from 2300-0600, but the exact times may vary according to local conditions and arrangements. Under a Grandfather clause, some airports may allow a number of landings (but generally not take-offs) between 2300-2359 and 0500-0600 (often termed shoulder periods), or some other variation or combination. In terms of operating aircraft to suit curfew restrictions, a whole set of rules typically applies to the precise times that an aircraft needs to request and be given pushback, taxi and/ or take-off clearance, or is required to become airborne and cross the airport fence, prior to the commencement of the curfew period. Further, the direction of the duty runway may also be restrictive for take-offs and/or landings, due to the incidence of noise over nearby community areas. So, if a nominated runway is not suitable due to wind or other conditions, operations may not be permitted.

There is usually a system of monetary fines for curfew breaches and despite this, an airline may occasionally elect to depart late and pay the fine (provided they have АТС clearance to operate, of course). The rationale is that should a late-night take-off not occur, the cost and disruptive effects of cancelling the service with the resultant wait for the crew to take crew rest, likely hotel accommodation, shortage of an aircraft in the network, missed connections at the destination, and any other consequential flow-on, may be well in excess of the fine. There may be a system of dispensation available, whereby in an extenuating circumstance, such as the occurrence of a wide-ranging and unpredicted disruption (major weather event) leading up to a significant holiday period (e.g., major religious events), the commencement of curfew may be relaxed by, say, 30 minutes. This type of dispensation is most likely to rely on a government departmental approval system but may in extreme cases require a higher level of government sanction. Other than curfew restrictions, there may also be limitations as to the availability of control tower staff, such that the tower (and therefore ability to authorise landings or take-offs) is only available at particular times. In some dual civil/military airports, АТС services are provided by the military, thereby governing operational hours.

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