You can meet a daily demand of 400 people with a single large aircraft, or with a smaller aircraft making four flights a day. The capacity offered is the same, but the result is very different for both the passenger and the airline. So how does an airline decide which aircraft to fly where and at what time? In this lesson we examine, step by step, what a flight schedule is, the internal and external factors that affect schedule planning, the stages of the schedule planning process, the relationship of the scheduling unit with other units and the external factors that constrain the schedule.

What will you learn in this episode?

• To define the flight schedule and its components and explain why schedule planning is important
• To list the internal and external factors that affect schedule planning
• To explain the stages of the schedule planning process
• To explain with examples the relationship between frequency and aircraft size and the effect of aircraft turnaround time on the schedule
• To explain the relationship of the schedule planning unit with the operations coordination center, crew planning, maintenance and marketing units
• To explain the factors that constrain the schedule, such as slot regulations, airport operating hours, connecting flights and station staff

Summary of this episode

1. What is a schedule and why is it important?

Definition (schedule): In airlines, the schedule is the arrangement of when, how often, and with which aircraft type and staff the points in the flight network will be connected, taking economic and operational factors into account.

Components of the schedule: flight number, departure and arrival points, departure and arrival times, daily and weekly frequency and the aircraft type that will operate the flight.

Definition (schedule planning): It is the process in which decisions are made on how to use the airline's most valuable and scarcest resources, the aircraft and the flight crew.

Why is it critically important? The schedule-based components of the product determine perceived service quality, demand, market share, profitability and competitiveness; together with the network structure, they also affect costs.

Both art and science: On the one hand, the quality and quantity of the service that will meet customers' wishes and needs are determined; on the other hand, increasing revenues and minimizing operating costs are targeted.

Its place in the process: Schedule planning follows fleet planning; reservations and sales follow the schedule.

Timing: Schedule development starts a year or more before the flight; departure times are usually finalized 2–6 months in advance, but last-minute changes can also be made for reasons such as weather conditions. That is why schedule planning is a dynamic process.

2. Internal factors that affect the schedule

The most important factor: It is which markets will be served, when and how often; because these determine the time utility the passenger will gain.

Maintenance: Aircraft need scheduled maintenance even if they make only one flight; some tasks, such as corrosion checks, must be done according to the calendar even if the aircraft does not fly at all. An aircraft in maintenance cannot earn revenue; that is why the maintenance program and the schedule must be in harmony.

Definition (availability): It is the share of time in which the aircraft is ready to be used on revenue-generating flights; it should be kept at the highest level.

Staff: Which aircraft types pilots can fly, their numbers, their training status and daily, weekly, monthly and yearly flight time limits directly limit the schedule; similar factors apply to cabin crew.

3. External factors that affect the schedule

Definition: These are factors that remain largely outside the airline's control.

Airport facilities: The suitability of gates for the aircraft in the fleet, the availability of check-in counters, baggage and ground handling equipment and airport capacity can constrain the schedule.

Competition: Competitors' schedules and the competitive dynamics in the market are also taken into account. Example: If frequency is an important competitive tool in a market, the airline may have to increase its own frequency.

Comparison (internal and external): Internal factors (maintenance, staff) arise from the airline's own resources; external factors (airport facilities, competitors) are outside the airline's control.

4. The schedule planning process: airport pairs and frequency

First stage, determining airport pairs: This means the airline deciding which product it will produce; its most important input is which markets have demand, and it is related to the design of the network structure.

Second stage, determining frequency: Frequency is one of the most important factors affecting total travel time, and therefore an important determinant of demand and a competitive tool.

Definition (frequency): It is the number of daily or weekly flights on a given route.

What does the right frequency depend on? On the competitive strategy, demand forecasts, and market share, unit cost and unit revenue targets. Frequency and aircraft type are determined together.

Example: Meeting a daily demand of 400 people with a 400-seat aircraft once a day or with a 100-seat aircraft four times a day offers the same ASK. Flights at four different times shorten total travel time by offering the passenger an option close to the desired time, and may be preferred more.

Trade-off: Increasing frequency can lower the average load factor and raise unit costs. Schedule planners constantly balance this trade-off.

5. The schedule planning process: timing

Third stage, timing of departures and arrivals: The most important factor is at what time passengers want to set off or be at their destination.

Why can't all flights be placed at peak hours? Airlines first prefer the time windows when demand is high; however, because of the fleet, aircraft assignment and airport capacity, not all departures can be placed at peak hours. A balance must be struck between aircraft productivity and passenger needs.

Definition (aircraft turnaround time): It is the shortest preparation time an aircraft needs at an airport for disembarking and boarding passengers, fueling, cleaning and maintenance tasks.

Example: According to the source, preparing a 100-seat domestic aircraft can take 20–30 minutes, while preparing a 400-seat aircraft used on international routes can take up to two hours.

Effect of turnaround time: As turnaround time gets longer, daily aircraft productivity falls; that is why planners arrange off-peak flights in a way that allows aircraft to be used on high-demand routes and at high-demand times.

Time zones: On long routes, time zone differences also constrain the choice of the best departure time.

Chain effect: Even a small disruption can affect connections, aircraft and staff assignments and maintenance programs.

6. The schedule planning process: aircraft and crew assignment

Fourth stage, aircraft assignment (fleet assignment): It is determining which aircraft type will be assigned to each flight leg. The aim is to place on the route the aircraft that will provide the highest revenue at the lowest operating cost.

What is taken into account? In addition to revenue and cost, runway characteristics, flight distance, fuel capacity and meteorological conditions. Large airlines make this decision with mathematical optimization models; in markets where capacity has been set in advance, aircraft with a seat count that fits the regulation are assigned.

Definition (flight rotation): It is the chain of consecutive flights formed when the destination of one flight becomes the starting point of the next flight; each aircraft's consecutive flights are determined while also taking maintenance needs into account.

What does lowest cost mean? In weekly aircraft rotations, lowest cost means not only operating cost but also the opportunity cost of insufficient output that cannot meet demand. Some airlines switch to a larger or smaller aircraft close to the operation, depending on demand.

Fifth stage, crew assignment: It consists of three steps:

• crew pairing: forming flight crew pairs of captains and first officers within the rules,
• crew rostering: preparing each crew member's personal flight program while taking factors such as leave, training and medical checks into account,
• crew recovery: rebuilding crews that have been disrupted.

Rules observed: The flight time limits and certification requirements set by the authorities are observed; to reduce layover costs, efforts are made to have crews spend the night at the home base as much as possible.

7. Relationship of the scheduling unit with other units

Way of working: The schedule planning unit distributes its draft to the relevant units and receives feedback; in most airlines, working committees are set up for this. The aim is a schedule that ensures customer satisfaction, contributes to profitability and creates a competitive advantage.

Definition (operations coordination center; OCC): It is the unit responsible for implementing the prepared schedule and operating flights on time (Operations Coordination Center).

Comparison (scheduling unit and OCC): The scheduling unit is responsible for preparing the schedule and tries to minimize cost and maximize productivity; the OCC is responsible for implementing the schedule and tries to operate flights without delays and cancellations. Because a very tight schedule makes on-time operation difficult, the two aims must be balanced. The schedule is handed over to the OCC shortly before the operation.

Crew planning and maintenance: Because human resources cost is the largest item after fuel, close coordination is needed with the crew planning unit, and with the maintenance production planning unit for the place and time of heavy maintenance.

Marketing: The marketing unit shapes schedule-related product components such as frequency, times and total travel time according to customer needs. Example: While business travelers want high frequency and convenient times, minimizing costs comes to the fore in schedules aimed at price-sensitive leisure travelers.

Long routes and cargo: On long routes, arrival time becomes more important than departure time. Airlines that carry freight with cargo aircraft arrange the schedule according to shippers' needs, for example night hours.

8. External factors that constrain the schedule

Slot regulations: They are used to ensure a smooth air traffic flow by matching demand to available capacity, and they apply at airports and in time windows with capacity problems.

Definition (en-route slot): It is the time interval in which an aircraft is allowed to fly a section of a set route; in European airspace it is allocated by Eurocontrol.

Definition (airport slot): It is the time window allocated for using the airport and related services for landing or takeoff.

Slots and bilateral agreements: Slot allocation is independent of bilateral agreements; a designated airline that cannot obtain slots may in practice be unable to enter that airport.

Definition (airport operating hours; curfew): These are the hours during which the airport is open to flights; outside these hours flights are prohibited or limited. According to the source, many airports are usually closed between 23:00 and 06:00 or allow only quiet aircraft.

Connecting flights: In airlines using a hub-and-spoke network, connecting flights make it necessary to plan departures from spoke airports according to departure times at the hub.

Station staff: Example: If a team of 10 people is needed for one aircraft, planning two aircraft in the same half hour requires extra staff; that is why it may be preferred that flights do not fall into the same time window.

Other factors: Climate characteristics, the number of jet bridges and suitable ground equipment are also taken into account.

In short

Schedule planning is a process that is both art and science at the same time, deciding in which market, at what frequency and at what time scarce resources such as aircraft and flight crew will be used. A constant balance is struck between frequency and load factor, and between passenger needs and aircraft productivity. Maintenance, staff, airport capacity, slots and operating hours limit this balance; a successful schedule emerges only through coordination between units.

Key concepts

• Schedule: The arrangement of when, how often, and with which aircraft type and staff the points in the flight network will be connected.
• Schedule planning: The process in which decisions are made on how to use aircraft and flight crew, aiming to minimize costs while increasing revenues.
• Availability: The share of time in which the aircraft is ready to be used on revenue-generating flights.
• Frequency: The number of daily or weekly flights on a given route; an important determinant of demand and a competitive tool.
• Aircraft turnaround time: The shortest preparation time an aircraft needs at an airport for disembarking and boarding passengers, fueling, cleaning and maintenance tasks.
• Aircraft assignment: Determining, for each flight leg, the aircraft type that will provide the highest revenue at the lowest cost.
• Flight rotation: The chain of consecutive flights formed when the destination of one flight becomes the starting point of the next flight.
• Crew pairing: Forming flight crew pairs of captains and first officers within the rules.
• Crew rostering: Preparing each crew member's personal flight program while taking factors such as leave, training and medical checks into account.
• Operations coordination center (OCC): The unit responsible for implementing the prepared schedule and operating flights on time.
• En-route slot: The time interval in which an aircraft is allowed to fly a section of a set route.
• Airport slot: The time window allocated for using the airport and related services for landing or takeoff.
• Airport operating hours (curfew): The hours during which the airport is open to flights; outside these hours flights are prohibited or limited.

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Sources used:
Battal, Ü. (2016). Havayolu işletmelerinde filo ve tarife planlaması. E. Gerede ve A. E. Demirci (Ed.), Havayolu Yönetimi (6. Ünite) içinde. Eskişehir: Anadolu Üniversitesi Yayınları.

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