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The Commercial Schedule
Airlines plan their operations years ahead of the current day. From a determination of the cities to be served, network design and desired route structure, and following a long, exhaustive process to ensure all relevant considerations have been taken into account, a flight schedule will emerge. Commonly, airlines will produce a major timetable according to summer and winter periods. This is largely due to significant changes in seasonal weather, and holiday period durations, particularly in the northern hemisphere, leading to significant changes in demand for travel. Thus, the process will be a function of the regulatory framework, market demands, required aircraft mix with any operational performance and limitations, resources and manpower, and competition.3 At first, the schedule will be an ill-defined set of flights that, over many months, will be manipulated and modified to meet more exacting commercial targets within a multitude of constraints and limitations. Similarly, the operational aspects are also planned in significant detail, right up to the evening prior to the day of operation. Hence, operational preparedness is essential to optimising the day’s operation as planned. In the count-down to the day of operations, there are numerous challenges to be faced, due to competing demands primarily from the airline’s own commercial and engineering activity, but also from outside demands such as АТС or airport gate resources. Considerations within the many functional areas of the IOC must take into account demands for resources that may be based, for example, on contractual arrangements (e.g., Pilots, Flight Attendants, Engineers).
The Schedules Planning (Scheduling) Department’s task is to build, develop and then fine-tune the flight schedules to the point of maximum utility. This translates to having met all legal and regulatory limitations, corporate and commercial objectives (such as achieving target load factors and target market share), and realising optimal efficiency regarding use of resources, all with the utmost in customer focus at the forefront. At the point of handover from the Scheduling Department to the IOC, all these objectives and more should be met. The extensive build-up of the schedule will also have incorporated the ideal utilisation of Pilot and Flight Attendant crews, taken into account available resources with inbuilt capacity to cover contingencies, met any maintenance requirements for servicing, repair, or other considerations, considered any airport and airspace restrictions, and so forth.
Part of the task of building a schedule is programming flights to meet the commercial objectives such as capacity required for a city-pair (route), frequency and timing of flights, and provision of connection times to enable travel across the network. The schedule that is produced is manifested in terms of an operational utilisation of aircraft, displaying sequences of flights in a chronological order of operating time. So, operating patterns of flights emerge which may all fit essentially within one day for a domestic schedule, or span across several days for a flag (international) carrier. These patterns of flights are initially assigned to an aircraft type, rather than an individual aircraft registration or tail number; a process that occurs much closer to the actual day of operation. Building up these patterns takes into account the requirements for matching demand across each city-pair or route, with capacity (right aircraft on the right route). Of course, Scheduling must be cognisant of the capabilities of the chosen aircraft type, as the aircraft must be able to operate the route structure with the right performance characteristics to carry the required payload. This is a very iterative process, continuously evolving and changing.
As demand fluctuates, the capacity-matching process needs to adapt, with the result that the schedule build-up process is in a very fluid state for a long time. In addition, changes to types of aircraft being matched against demand call for changes to the crew allocations and patterns (especially pilots), further complicating the process. A third player; the Engineering or Maintenance Department, also plays a key role, as planned maintenance work needs to be considered in the schedule-building process to ensure the fleet remains capable of meeting the operating requirements. In larger fleets, it is common for a number of aircraft to be excluded from the composition of the schedule, to allow for rotating several airframes through heavy maintenance. Where possible, the maximum number of aircraft are programmed to be available to meet peak travel demands such as major events and holiday periods. In some fleets, though, where all fleet units are committed to flying patterns, or in the case of smaller airlines with low fleet numbers, this may be less feasible.
Commercial and operational nexus
It can be appreciated from the above points, that the nexus between the Commercial Scheduling Department, and the operational areas, predominantly Operations Control, Crewing (both Pilot and Flight Attendants) and Engineering Departments is challenged at times due to the differing philosophies underpinning their functions. To reach commercial objectives, schedules may be designed in such a way that results in operational inefficiencies or exposes the future operation to weakness in the face of disruption. For example, if a number of ‘tight’ schedules requires precise crewing connections between a number of flights, with little alternative crewing solution, such that a delay to a key flight may compromise these connections, the consequential effects could be widespread, with little room for effecting a fitting recovery. So, the schedule-build process needs involvement from all stakeholders, whose specific interests and concerns need to be considered thoroughly, as alienating any part of this relationship will lead to suboptimal outcomes.
Robustness refers to the ability of a schedule to withstand disruptive shocks during a day of operation. Schedules are built according to commercial demand that results in a series of programmed flights ideally having an optimum yield of passengers and meeting commercial targets such as desired load factors and market shares. Hence, flight timings where possible, and depending on the business model operated by the airline, may be tuned to customer preferences, such as satisfying peak demands (e.g., morning or afternoon business), providing attractive departure and arrival times, and suitable levels of frequency. From an operational point of view, there are a number of subtle ways schedules can be fine-tuned to add robustness and help the IOC manage on the day of operation. For example, extending the total schedule time (departure to arrival) can help to alleviate ground-holding times at busy airports, and scheduling additional ground time between flights (called buffering) can assist in recovery from late-running flights.
Besides meeting the constraints above, robustness should also take into account opportunities for swapping aircraft of the same type (like for like), enabling greater flexibility in day-to-day operations. This degree of flexibility may also satisfy requests by Crewing to facilitate crew connections between flights, or by Engineering for particular aircraft registrations (tails) to be committed to particular patterns or to particular ports for maintenance work. Further, flexibility may enable better efficiencies in gate allocation in major ports. Sometimes, the schedule build results in lengthy dwell times at airports (e.g., a turnaround time of 5, 12 or longer, hours). The volume of traffic expected to use the parking gates at some airports often requires aircraft to be towed offline and parked remotely until the next scheduled commitment. This time is also used on occasions for maintenance work. Depending on the configuration of the airport facilities, towing times may be implicated in delaying outbound flights.