AIRLINE MANAGEMENT
Chapter 6: Schedule Planning
1 Outline Airline Planning Stage Schedule Development Frequency Planning Timetable Development Constrains of timetable development Schedule Map Fleet Assignment and Aircraft Rotations Spill
2 Airline Planning
Fleet Planning
Route Planning
Schedule Development Frequency Planning Timetable development Fleet Assignment Aircraft rotations
Pricing Crew Scheduling
Revenue Airport Management Management
Sales and Operations Control 3
Short Term Long Term Long Term Short Distribution Tactical Strategic Strategic Tactical
Source:Prof. Dr. Barnhart Time horizons prior to departure date
Time horizons of different planning stages prior to departure date
Fleet planning – 2 - 5 years Route planning-evaluation – 1 - 2 years Schedule developments – 2 - 6 months Pricing , Revenue management – more tactical
Even closer to departure 4 Airline Planning First Question to Answer for an Airline Planning
Fleet Planning: Aircraft preference which type of aircraft to acquire/retire? when? and how many of each?
5 Airline Planning The second Question to Answer for an Airline Planning
Route Evaluation: Network structure type City-pairs to be served Where to fly?
6 Schedule Development The Third Question to Answer for an Airline Planning Schedule Development; Involves four different but interrelated task
1-Frequency planning:
How often should the airline operate flights on the selected routes?
Number of departures to be offered on each route
Non-stop vs. multi-stop 7 Schedule Development The Third Question to Answer for an Airline Planning Schedule Development; Involves four different but interrelated task
2-Timetable Development:
At what times should flights departures be scheduled ?
Flight departure and arrival times
8 Schedule Development The Third Question to Answer for an Airline Planning Schedule Development; Involves four different but interrelated task
3-Fleet Assignment:
What type of aircraft should be used for each departure time?
Aircraft type for each flight, based on demand and operating cost estimates 9 Schedule Development The Third Question to Answer for an Airline Planning Schedule Development; Involves four different but interrelated task
4-Aircraft Rotation Planning:
How should each aircraft type be flown over the airline’s network in order to balance of aircraft arrivals and departures at each airport?
Links consecutive flights to ensure balanced aircraft10 flows on the network Schedule Development
The schedule development process begins a year or more in advance of flight departure, and can continue until actual departure time. Frequency plans are established based both on;
route evaluations -a year or more in advance and fleet planning decisions - 2–5 years earlier. Specific timetables and aircraft rotation plans are developed up to 1 year in advance, finalized 2–6 months before departure. Final revisions closer to departure Unexpected operational constraints such as maintenance, weather can necessitate schedule changes and irregular operation planning 11 until the flight actually departs. Frequency Planning Frequency planning: How often should the airline operate flights on the selected routes? frequency is how many services in a set time period an airline may provide. Increases in the frequency on a route improve the convenience of passengers. Result in higher traffic and revenues and and increased market share Airline frequency share is more important to capturing time- sensitive business travelers
Peak departure times as early morning and late afternoon are most attractive to a large proportion of business travelers in many market 12 Frequency Planning More frequent departures reduce the schedule displacement or “wait time” between flights and reduce the total trip time.
Total Trip time: the total time of Access and egress times to/from airports at origin and destination Pre-departure and post-arrival processing times at each airport Actual flight times plus connecting times between flights
Total trip time=time (fixed)+time(flight)+schedule displacement
Schedule displacement = K / frequency 13 Frequency Planning As actual flight time dominates “schedule displacement ” or wait time” in long-haul routes, frequency is more important in short-haul routes than for long-haul routes.
Path Quality -non-stop flights vs. connecting flights. It is an important parameter affects market share. Usually Non-stop flights preferred over one-stop, connecting flights or interline connects etc. Remember the advantages of Point-to-point flights reducing total travel time, primarily by eliminating the intermediate stop. However, Frequency of departures can be as important as path quality (non-stop vs. connecting) in many cases14 . Frequency Planning What affect frequency of departure decision? Demand forecasts and competition drive the frequency of flights on a route: 1- Estimates of total demand between origin and destination 2- Expected market share of total demand, which is determined by frequency share relative to competitors 3-Potential for additional traffic from connecting flights affect the frequency decision. If connecting passengers represent a substantial proportion of expected traffic flow on the route, the airline can decide to offer even greater frequency of departures and/or
operate larger aircraft with lower CASK. 15 S-Curve Affect Market Share vs. Frequency share Frequency increases market share - revenues
disproportionately because of S-curve effect. Carrier’s share of market traffic market share traffic of Carrier’s
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Carrier’s share of total flights in the market S-Curve Affect
Market Share vs. Frequency share The S-curve relationship between frequency and market share shows how frequency is important for competition. In a two-airline competitive market, if one airline offers 60% of the non-stop flights , it is likely to capture more than 60% of the market share. Conversely, the other airline with 40% frequency share will have less than 40% market share. The extent of this disproportionate response of market share to frequency share will depend on the degree to which the S-curve bends away from the market share = frequency share diagonal line 17 S-Curve Affect Market Share vs. Frequency share Because of the S-curve effect , competing airlines are in tendency of matching each other in terms of frequencies in many non-stop markets, to maintain their market share.
As long as both airlines in a two-carrier market offer the same number of departures- same frequency , they will both capture approximately half of the market demand.
In a three-carrier market, the tendency would be for all three airlines to offer 33% of the frequency share, to retain approximately 33% of the market share. 18 Frequency Planning
“Load consolidation” affects frequency and aircraft size decisions:
Single flight with multiple stops provides service to several O&D markets at the same time. Load consolidation allows airline to operate higher frequency - increasing its market share and/or larger aircraft - reducing its unit operating costs. Consolidate loads is a fundamental reason for economic success of airline hubs.
19 Frequency Planning
Seasonal variations in demand effect frequency planning More frequent flights during peak seasons Airline might lease additional aircrafts in that period. Airline requires some aircraft to be shifted from off- peak routes Some routes might only be served during peak season
Business vs. leisure mix of demand Short-haul business routes typically require more frequency; usually with smaller aircraft.
20 Frequency Planning Although frequency planning is separated from the choice of aircraft type for each flight on the route (i.e., “fleet assignment”), the two decisions are interrelated. The airline’s supply decision for a route consists of two choices ; The number of departures per day and The number of seats to be offered on each departure. If the demand estimates for a route suggest that 400 seats per day are required, the airline can choose one of those: Decision 1: One frequency per day with a 400-seat aircraft or Decision 2: 4 frequencies per day with a 100-seat aircraft. Although both choices supply 400 seats per day to the route, The outcome in terms of this airline’s market share, passengers carried and revenues will be very different, especially if there is a competitor on the route that operates 4 flights per day. 21 Frequency Planning In this example, Decision 1 (one flight with 400 seats) will almost certainly give the airline a relatively low market share due to its low-frequency (20%) share, with prices and quality of service equal. Such a low market share would not likely allow the airline to fill its 400-seat aircraft to profitable levels. This example illustrates how frequency planning can be influenced by the presence and frequency of the competitors. This example also illustrates how airlines have little choice rather than operating smaller-capacity aircraft with higher operating costs per seat kilometer in competitive markets, especially those involving relatively short-haul routes
22 Timetable Development Given a chosen frequency of service on each route, the next step in the schedule development process is to generate a specific timetable of flight departures. First chose of the airline is to provide departures at peak periods (09:00 and 17:00), especially on routes that serve business demand. However, not all departures can be at peak periods on all possible routes, given aircraft fleet and rotation considerations. Most airlines do not have enough aircraft to allow them to schedule departures on each route in their network for example at 09:00.
23 Timetable Development a trade-off in Timetable Development maximization of aircraft utilization vs. schedule convenience for the passengers. The timetable must include minimum “turnaround” times required at each airport to disembark and embark passengers, refuel and clean aircraft. Minimum turnaround times will vary by aircraft type and the characteristics of the flights (domestic or international flights.) A 100-seat aircraft for domestic flights can be turned around within 20–30 minutes A 400-seat aircraft for international flights can take 2 hours or more to turn around. 24 Timetable Development
Aircraft utilization Measure of aircraft productivity. calculated by dividing aircraft block hours by the number of aircraft days assigned to service on air carrier routes. Typically presented in block hours per day.
Block Hour Time from the moment the aircraft door closes at departure of a revenue flight until the moment the aircraft door opens at the arrival gate following its landing. Block hours are the industry standard measure of
aircraft utilization 25 Timetable Development Aircraft turnaround time –TAT is the time between the aircraft has reached the airport terminal with the engines shut down until the time the engines start. During this period of time, there are lot of tasks that are needed to be carried out such as refuelling, loading and unloading baggages, embarking and disembarking of passengers, servicing and maintenance. Roughly, 30% of the delays of the aircraft departure occur during aircraft turnaround time. One of the main reasons is the number of tasks that are needed to be carried out. The delays during take-off and during landing are significantly lower than delays due to aircraft TAT because the only risk that aircraft faces during take-off/landing is the local weather conditions and some minor technical issues. While for the technical issue normally will occur before
departure and it will consider as the delay during aircraft 26 TAT. Timetable Development Even if minimum turnaround times are met, the earliest departure time for the next flight might not be desirable in terms of schedule quality. For example, an 09:00 departure from city A with an 11:00 arrival at B and a 60-minute minimum turnaround time results in a possible departure time for the aircraft from B at 12:00. If this aircraft is to return to A, a 12:00 departure will be off peak and have potentially lower demand, So it might be decided keeping the aircraft on the ground until the next peak period It reduces aircraft utilization and increases unit operating costs as fixed costs are spread over fewer seat kilometers. 27 Timetable Development Most airlines choose to maximize aircraft utilization in establishing a timetable of scheduled flight departures. The tendency is to keep turnaround times to a minimum and to use aircraft as much as possible. So, Airlines Schedule off-peak flights with low LF to keep the frequency share and to position aircraft for peak flights at other cities. Leave little buffer time for maintenance and weather delays to maximize aircraft utilization.
28 It can also result in many low LF flights and reduced airline profitability Timetable Development Some additional factors constrain an airline’s timetable development. Hub operation: Hub networks operate on a “fixed bank” basis and require flights arrive from spoke cities within a prescribed time range, for passenger connections. This requirement leaves relatively little flexibility for scheduling departures from the spoke city to the hub, if the flights are expected to provide service to both local and connecting passengers. Time zone differences also limit feasible departure times, especially on long-haul routes. For example, flights from eastern cities in North America to Europe typically do not depart before 16:00, as passengers do not want to arrive at their European destination in the middle of the night. Their departure time usually around 09:00 from North
America to Europe to arrive in Europe no later than 22:00 or29 23:00 Timetable Development Regulatory constraints such as airport arrival and departure slot times , airport curfews can limit the scheduling flexibility for an airline. Crew scheduling and routine maintenance requirements also have impacts on timetable development. Example: if an airline operates a single daily flight into an airport, arriving late in the evening , The subsequent departure of the same aircraft and crew cannot be scheduled for the next morning until minimum crew rest requirements have been met. The alternative for the airline is to schedule the aircraft to depart very early the next morning with a new crew, but this requires long layover time for each crew, that increasing crew cost 30 Timetable Development Increased block times can improve on-time arrival performance for airline, but has costs: Reduced utilization of aircraft and crew resources Lower position on GDS display screens Potential frustration for passengers with “early” arrivals
Each timetable shift has multiple impacts Previous and subsequent flights operated by same aircraft might also have to be shifted Feasibility of crews, gates, maintenance, curfews, etc. Potential demand and revenue impacts via Time of Day Demand and GDS displays
31 Schedule Map
The timetable and aircraft rotation plan in an airline’s schedule can be represented graphically by a “schedule map” .
the horizontal axis reflects the movement of aircraft from one airport to another and the vertical axis reflects movement in time.
32 Schedule Map
FRA MAD STO AMS 07:00 07:00 10:00 10:30 13:30 15:00 17:00
19:00 19:00 21:00
23:30 33 Schedule Map Schedule maps show flight legs containing aircraft movement in terms of both geography and time An example of a schedule map: This example is a schedule map, for an airline that operates two aircraft with the same type. This schedule map shows a timetable with a balanced aircraft rotation plan. One aircraft begins its day at Stockholm (STO) and flies to Frankfurt (FRA), then to Madrid (MAD), back to FRA, then to Amsterdam (AMS), and back to FRA and finally MAD. This aircraft then overnights at MAD, before flying a second day in this rotation, from MAD to FRA to AMS to FRA and back to STO. The schedule map illustrates a two-day aircraft rotation that begins and ends in STO – the same aircraft (“tail number”) will operate the 07:00 departure out of STO every second day. Therefore, for the airline to operate each of the flights on the schedule map daily, it needs two aircraft of the same type 34 Schedule Map
This example also illustrates several of the challenges in the development of a feasible schedule, given operational and marketing constraints. In this example, we have assumed that the airline must deliver and receive connecting passengers traveling to many other destinations, at the FRA hub. The connecting banks at FRA are fixed, shown by the blue ovals at FRA in the chart, so that our airline must have its feeder flights arrive and depart at FRA only during the connecting bank periods. Other constraints is minimum turnaround times at each station, 60 minutes for this example.
35 Schedule Map During the first day of the aircraft rotation plan shown on the schedule map, the aircraft that departs STO at 07:00 visit FRA hub three times during designated connecting bank periods, operates six flight legs, and accumulates 11.5 block hours of utilization. All turnaround times are at the minimum 60-minute constraint. On the second day of this rotation plan, however, the aircraft operates only four flight legs for 6.5 block hours, as scheduling constraints limit its utilization. First, the aircraft arrives in AMS from FRA at 11:30 but must sit on the ground until 15:00 for the next connecting bank at FRA. This is a good illustration of the utilization penalties on short hub–spoke network. 36 Schedule Map The aircraft spends 3.5 hours on the ground at AMS, above the minimum 60-minute turn time. Second, the aircraft departs from the FRA hub at 17:00 and arrives at STO at 19:00 to be in position for the next morning’s 07:00 departure to ensure a balanced schedule. By ending day , the aircraft sits idle for several hours in the evening that although it might have been used to generate additional utilization. On the other hand, this “early” end to the aircraft’s day at STO might allow for overnight maintenance to be performed. It might also give the enough crew rest time to depart the next morning on the 07:00 flight, thereby
reducing crew costs. 37 Schedule Map In the schedule map shown, the airline’s fleet of two aircraft operates on average five flight legs per day with an average daily utilization of 9.0 hours. It might not be the “best” solution to this scheduling problem and it is not the only feasible solution As shown Schedule maps are a visual representation of flight legs that incorporate aircraft movement in terms of both geography and time. In the early days of airline planning, schedule maps were covering on the walls of scheduling departments. Today, computer programmes linked to extensive fleet, route and timetable databases, allow the analysts on specific flight legs to make changes to the timetable. Programmes calculate the minimum number of aircraft required to operate the new schedule and can inform the analyst of any constraints (crew rules, maintenance requirements, passenger connection times). 38 Fleet Assignment and Aircraft Rotations The fleet assignment problem is to determine the type of aircraft to be flown on each flight leg departure, given network of routes and specified timetable of flights. “Fleet assignment” should not be confused with “fleet planning” Fleet assignment is a tactical decision made after an initial timetable has been developed, longer- term decisions about fleet planning and route planning/evaluation have been made. Fleet assignment is limited to a choice of aircraft types from the airline’s existing fleet. 39 Fleet Assignment and Aircraft Rotations
is to minimize the combined costs of “spill” (rejected demand) and aircraft operating costs.
Here there is trade off between operating costs and spill
Typically, Operating costs increase with size of airplane
Larger aircraft have higher ownership and maintenance costs Increased fuel consumption with greater capacity and weight 40 More and probably higher paid crew members required Spill Spill: the number of passengers unable to book a seat due to insufficient capacity Also call as Rejected demand
Spill occurs when potential demand for a flight leg is greater than the physical capacity of the aircraft.
41 Spill F(x)
number of passenger
42 Spill
43 Fleet Assignment and Aircraft Rotations Spill- ‘rejected demand ’costs decrease with size of airplane SPILL is rejected demand due to inadequate capacity Spill occurs when the aircraft assigned to a flight is too small and potential demand and revenues are lost . Spill is the loss of bookings when the flight has been fully booked to capacity. The magnitude of spill is difficult to measure, but can be estimated using “Spill Models”. Spill can be reduce or eliminated by assigning a large aircraft to accommodate all possible peak day demands
44 Fleet Assignment and Aircraft Rotations
there is trade off between operating costs and spill
Larger aircraft have higher operating costs and will fly with many empty seats on most non-peak days.
Larger aircraft accommodate more demand and generate more revenue, meaning less spill and lower spill costs.
45 Fleet Assignment and Aircraft Rotations
There are some fleet assignment techniques such as single leg and network fleet assignment. Airlines have fleet assignment models based on large- scale mathematical network optimization methods. These computer models optimally assign aircraft so as; to minimize spill costs plus operating costs and/or; to maximize profitability , with constraints such as minimum ground times, maintenance requirements, number of aircraft by type available in the airline’s fleet.
46 Fleet Assignment and Aircraft Rotations Aircraft rotation constraints in the fleet assignment model formulations ensure feasible aircraft cycles and balance of aircraft inflow/outflow at each airport. However, even with fleet assignment optimization models, it is not possible to achieve a perfect match of seats with demand on each flight in the timetable, given the need to balance the flow of aircraft over the entire airline network. The optimal aircraft assignment is main target. The optimal aircraft assignment to a given flight might be too big or small for the demand on that flight but it can lead to maximum operating profit over the entire network. 47 Fleet Assignment and Aircraft Rotations
Consider this simple example: Assigning a 100-seat aircraft to a peak 09:00 departure from A to B and to the subsequent non-peak departure from B to A might result in spill from A to B on certain high-demand days, but LF on the return flight from B to A at the off-peak time might be very low. In this case, reducing spill on the first flight by operating a larger aircraft will only worsen the load factor performance of the return flight. The “optimal” aircraft size must consider two (or more) flights in the same aircraft rotation. 48 Fleet Assignment and Aircraft Rotations
Fleet assignment models also include fleet size and aircraft balance constraints. Aircraft routing models are used to assign specific aircraft “tail numbers” to each flight, creating rotations that satisfy aircraft maintenance requirements. The solutions to such optimization problems have allowed airlines to achieve higher aircraft utilization rates. However higher aircraft utilization achieved by minimizing turnaround times can also lead to less buffer time for recovering from unexpected
maintenance and weather delays. 49 Fleet Assignment and Aircraft Rotations The handling of “irregular operations” involves dynamic revisions to the planned schedule right up until the flight departs or is cancelled. Flight cancellations and deviations from the planned timetable of operations are decisions that are not made lightly by the airline. A single cancelled flight can seriously disrupt aircraft rotations, crew schedules and maintenance plans Under conditions of disruptions and/or flight cancellations, the primary objective for the airline is to return to “normal” operations as quickly as possible. In this effort to get the airline back on plan, flight cancellations or aircraft re-routing sometimes take precedence over passenger convenience. 50 Some concepts Flight Leg (or “flight sector” or “flight segment”) : Non-stop operation of an aircraft between A and B, with associated departure and arrival time
Flight : One or more flight legs operated consecutively by a single aircraft (usually) and labeled with a single flight number (usually)
Route : Consecutive links in a network served by single flight numbers
Passenger Paths or Itineraries : Combination of flight legs chosen by passengers in an O&D market (e.g., AMS-DXB via connection at IST)
Buffer time : the time between flights that gives the ability the system to recover delays. This means that a higher punctuality and customer satisfaction can be obtained.
Irregular operations (IROP): a situation in which a flight does not operate as planned, on schedule, is canceled, or has a change of equipment so that not all passengers can be accommodated.
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