Post on 03-Jan-2016
Optimization in Airline Optimization in Airline SchedulingScheduling::
Successes, Challenges, Successes, Challenges, and New Directions and New Directions
Ellis L. Johnson
IMA Workshop on Travel IMA Workshop on Travel and Transportationand Transportation
Nov 14, 2002
2 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Airline Operations ResearchAirline Operations Research
Airlines have been a hotbed of ORAirlines have been a hotbed of OR Planning process over time Planning process over time
• Schedule and complex developmentSchedule and complex development• Fleet assignment and routingFleet assignment and routing• Yield management and passenger flowYield management and passenger flow• Crew pairing and bid lines Crew pairing and bid lines • Operations and recoveryOperations and recovery
Computational issuesComputational issues• All require solving large-scale All require solving large-scale
optimization problemsoptimization problems
3 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Airline OR SuccessesAirline OR Successes
Excess crew costs in the planning Excess crew costs in the planning process has been driven to 0-3%process has been driven to 0-3%• AA was 8-10% 15 yrs ago: now 0-2% AA was 8-10% 15 yrs ago: now 0-2% • Each 1% is worth about $10 million/yrEach 1% is worth about $10 million/yr
• 1997 had 9,000 pilots costing $1.2 billion1997 had 9,000 pilots costing $1.2 billion
• Larger schedules and complex rulesLarger schedules and complex rules
Fleet assignment has increased Fleet assignment has increased profit by $tens of millions/yrprofit by $tens of millions/yr
Yield management maintains Yield management maintains revenue despite low faresrevenue despite low fares
4 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Implementation of Airline ORImplementation of Airline OR
Cost reductions were initially Cost reductions were initially embraced, e.g. crew schedulingembraced, e.g. crew scheduling
All airlines will say that they are All airlines will say that they are unique, have a different culture, etc.unique, have a different culture, etc.
US pilots have strange pay structureUS pilots have strange pay structure• Asian and European pilots are simply Asian and European pilots are simply
(high) salaried employees (high) salaried employees • US pilots get paid for what they fly + US pilots get paid for what they fly +
minimum guarantees + conflictsminimum guarantees + conflicts
5 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Compartmentalization into SilosCompartmentalization into Silos
Making sequential plans is commonMaking sequential plans is common• Schedule -> FAM & Routing -> CrewSchedule -> FAM & Routing -> Crew• Pricing -> YM -> promotions & salesPricing -> YM -> promotions & sales
Has led to optimization within siloHas led to optimization within silo Too little feedback Too little feedback What is needed is integrated What is needed is integrated
planning over function and over timeplanning over function and over time• Operations experience does not feed Operations experience does not feed
back into the planning process back into the planning process
6 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Compartmentalization into SilosCompartmentalization into Silos
Each group thinks they are the most Each group thinks they are the most important planning groupimportant planning group• Pricing and marketing define the airlinePricing and marketing define the airline• YM is needed to keep the pricing guys YM is needed to keep the pricing guys
from giving away the airlinefrom giving away the airline• Schedules and complexes are productSchedules and complexes are product• Crews think the airline ends in cockpitCrews think the airline ends in cockpit
Strategic planning and global Strategic planning and global optimization are impossible in this optimization are impossible in this environment environment
7 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
How Has Airline OR SucceededHow Has Airline OR Succeeded
Very optimized in certain silosVery optimized in certain silos• Crew SchedulingCrew Scheduling• Fleet assignmentFleet assignment• Yield managementYield management
Savings and increased revenue has Savings and increased revenue has been very realbeen very real
Fleet assignment has as objective Fleet assignment has as objective revenue - cost of operating airplanesrevenue - cost of operating airplanes
YM is much needed and big successYM is much needed and big success
8 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Where to Find the Next Success?Where to Find the Next Success?
Decision tools in operations and Decision tools in operations and recovery from disruptionsrecovery from disruptions• Begins to integrate over time and can Begins to integrate over time and can
feed back into robust planningfeed back into robust planning
Schedule developmentSchedule development• Is driven by markets and strategyIs driven by markets and strategy
Integrate YM and FAM over timeIntegrate YM and FAM over time• Initiated at Sabre to better model Initiated at Sabre to better model
revenue but is not being done over timerevenue but is not being done over time
Look at entire crew processLook at entire crew process
9 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Operations and RecoveryOperations and Recovery
Integrated recovery must consider Integrated recovery must consider aircraft, airports, crews, passengersaircraft, airports, crews, passengers
Environment is dynamic and Environment is dynamic and uncertainties abounduncertainties abound
What about robust planning?What about robust planning?• Integration over timeIntegration over time• In reality is a huge stochastic programIn reality is a huge stochastic program
• Requires model for integrated recovery Requires model for integrated recovery
SimAir is a tool to study operations, SimAir is a tool to study operations, recovery, and robust planningrecovery, and robust planning
10 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Schedule DevelopmentSchedule Development
Is driven by markets and strategyIs driven by markets and strategy Was considered too important to Was considered too important to
turn over to a mere modelturn over to a mere model Tremendously important and Tremendously important and
complicated problem involving:complicated problem involving:• Market presenceMarket presence• Structure of complexesStructure of complexes• Fleets and crewsFleets and crews
11 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Integrate YM and FAMIntegrate YM and FAM
Has been initiated at Sabre to better Has been initiated at Sabre to better model revenue model revenue
One way of doing it over time is DOne way of doing it over time is D33
• It means demand driven dispatchIt means demand driven dispatch• Involves reassigning crew compatible Involves reassigning crew compatible
sub-fleets so as to better match sub-fleets so as to better match capacity to high revenue demandcapacity to high revenue demand
• Is a close to departure FAM Is a close to departure FAM
Ira Gershkof conceived JITIra Gershkof conceived JIT• Industry was not ready for itIndustry was not ready for it
12 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Crew: The Rest of The Story Crew: The Rest of The Story
Manpower planning, conflicts, Manpower planning, conflicts, overtime flying, and reservesovertime flying, and reserves
In US airlines as high as 30% of the In US airlines as high as 30% of the pilots may be on reserve bid linespilots may be on reserve bid lines• Actual flying is about 50% of usualActual flying is about 50% of usual• Of that flying, more than half is to cover Of that flying, more than half is to cover
conflicts and as little as 1/3 to flying to conflicts and as little as 1/3 to flying to cover disruptionscover disruptions
The “sleeper” issue: fatigue and The “sleeper” issue: fatigue and circadian rhythmcircadian rhythm
13 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Crew: The Rest of The Story Crew: The Rest of The Story
Milind G. SohoniMilind G. Sohoni T. Glenn BaileyT. Glenn Bailey Operations Research, Delta Technology Inc.Operations Research, Delta Technology Inc. Atlanta, GA 30354-1801Atlanta, GA 30354-1801
Helen CarterHelen Carter Crew Resource Analysis, Delta Air Lines Inc.Crew Resource Analysis, Delta Air Lines Inc. Atlanta, GA 30320Atlanta, GA 30320
Ellis L. JohnsonEllis L. Johnson Georgia Institute of Technology ISyEGeorgia Institute of Technology ISyE Atlanta, GA 30332-0205Atlanta, GA 30332-0205
14 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
1 - 5 years1 - 5 years 3 - 9 mos.3 - 9 mos. 1 - 1.5 mos.1 - 1.5 mos. DailyDaily
Delta Technologya wholly owned subsidiary
of
Ÿ B lock T im e F orecas tingŸ S chedu le G enera tionŸ F lee t A ss ignm en t
Ÿ N etw ork D eve lopm en tŸ F ligh t P ro fitab ilityŸ M arke t A na lys is
Long Range CrewManpow er Planning
Long Range Planning
Ÿ A irc ra ft R o ta tionŸ S lo t M anagem en t
Ÿ Crew PairingOptim ization
Ÿ Bidline GenerationŸ Bidding and Line
Aw ards
Ÿ V aca tion A ss ignm en tŸ V acancy B idd ing and
A w ards
Daily Operations
Ÿ Involuntary andVoluntary Flying
Ÿ Crew Recoveryduring IROPs
Ÿ A irc ra ft R ecove ryŸ P assenge r R ecovery
Pre-month Planning
Ÿ Initial TrainingScheduling
Ÿ Vacation Scheduling
Ÿ Recurrent TrainingScheduling
Ÿ Flight Instructor Scheduling
Airline Business Process -Time Line
Crew Planning Overview Crew Planning Overview
15 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Integrated Crew Planning
Crew Manpower Planning and Crew StaffingCrew Manpower Planning and Crew Staffing
Crew Pairing Bidline
Generation Bidding
TrainingScheduling
Sim Utilization New Hires
Vacation Scheduling
Daily Operational UtilizationDaily Operational Utilization
Expected UtilizationExpected Utilization
Feed B
ack
to L
ong R
ang
e P
lannin
gFe
ed B
ack
to L
ong R
ang
e P
lannin
g
Operational PlansOperational Plans
CONFLICTSCONFLICTS
16 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Crew Pre-Month Planning
Crew Pairing Optimization
Regular/Reserve Bidline Generation
Bidding and Conflict Resolution
Vacation Scheduling
Initial Training Scheduling
Tim
eTim
e
Recurrent Training Scheduling Flight Instructor Scheduling
Month of OperationMonth of Operation
Supplemental Regular Lines
17 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Reserve Demand
Net Reserve Net Reserve DemandDemand
(1) Vacation Conflict(1) Vacation Conflict (2) Initial Training Conflict(2) Initial Training Conflict (3) Transition Conflict(3) Transition Conflict (4) Recurrent Training (4) Recurrent Training ConflictConflict
(1) Weather Disruptions(1) Weather Disruptions (2) Aircraft Maintenance(2) Aircraft Maintenance (3) Sick Leave(3) Sick Leave
Open Time TripsOpen Time Trips
Voluntary FlyingVoluntary Flying Premium FlyingPremium Flying ReservesReserves
Pre-Month PlanningPre-Month Planning Irregular OperationsIrregular Operations
Could be up to 25%Could be up to 25%total trips builttotal trips built
Higher ReserveHigher ReserveAvailability DesiredAvailability Desired
Could cover 10% of the open trip flying
18 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Integrated Planning - Function & Time
Integrated Planning - Function & Time
Integrated planning breaks down silos Integrated planning breaks down silos
Integrated planning over time horizon?Integrated planning over time horizon?
• Current crew planning ends with bid linesCurrent crew planning ends with bid lines
• leaves it and goes on to the next monthleaves it and goes on to the next month
Is feedback on operations built in?Is feedback on operations built in?
Isn’t planning a multi-stage problem?Isn’t planning a multi-stage problem?
• Shouldn’t the plan at any stage depend on Shouldn’t the plan at any stage depend on
options and scenarios at the next stage?options and scenarios at the next stage?
• What is value of making decisions later?What is value of making decisions later?
19 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Overview – Crew Schedule ProcessOverview – Crew Schedule Process
Manpower planning 2-3 years out Manpower planning 2-3 years out
Pairings and bidlines for monthly planPairings and bidlines for monthly plan
Swaps, conflicts, and transitionSwaps, conflicts, and transition
• Pairings fall out and must be reassigned Pairings fall out and must be reassigned
Operations involves rescheduling Operations involves rescheduling
disrupted pairingsdisrupted pairings
• Voluntary overtime flying and reservesVoluntary overtime flying and reserves
20 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Manpower PlanningManpower Planning
Manpower planning 2-3 years out Manpower planning 2-3 years out
Pilots and positions by fleet and basePilots and positions by fleet and base
• Involves transitions – who requests moveInvolves transitions – who requests move
• Includes new hiresIncludes new hires
• Sensitive to changes in fleet plan Sensitive to changes in fleet plan
Vacation plan and recurrent training Vacation plan and recurrent training
Reserve staffing level included Reserve staffing level included
21 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Pairings and BidlinesPairings and Bidlines
Pairings and bidlines during month Pairings and bidlines during month
Pairings are in Pairings are in fleetfleet and for and for crew basecrew base
Swaps take place Swaps take place
Vacations, recurrent training, and Vacations, recurrent training, and
transition conflicts cause transition conflicts cause pairings to pairings to
drop outdrop out of the bidline of the bidline
In operations, In operations, pairings may be pairings may be
disrupted or dropped outdisrupted or dropped out
22 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Swaps, Conflicts, and TransitionSwaps, Conflicts, and Transition
Conflicts: vacation, training, transitionConflicts: vacation, training, transition
Uncovered pairingsUncovered pairings go to reserves go to reserves
• Reserve crew bidlinesReserve crew bidlines already assigned already assigned
• Reserves used in this way will be Reserves used in this way will be
unavailable in operationsunavailable in operations
Recurrent training may be assigned by Recurrent training may be assigned by
the airline after bidlines are assignedthe airline after bidlines are assigned
• Pairings that drop out are thus controlled Pairings that drop out are thus controlled
23 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Operations and RecoveryOperations and Recovery
Operations involves rescheduling for disruptions Operations involves rescheduling for disruptions
Reserves cover parts of pairings (usually ends) Reserves cover parts of pairings (usually ends)
and whole pairings typically from unprotected and whole pairings typically from unprotected
bidlines bidlines
However, voluntary overtime takes precedence However, voluntary overtime takes precedence
Premium overtime may be only option if no Premium overtime may be only option if no
reservesreserves
Crew recovery can swap crews (move-ups), cover Crew recovery can swap crews (move-ups), cover
part of a pairing with reserves, or send home part of a pairing with reserves, or send home
24 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Reserve Crew PlanningReserve Crew Planning
Spans the planning timelineSpans the planning timeline
Manpower planning allows for Manpower planning allows for
reserves ~25% reserves ~25%
Reserve bidlinesReserve bidlines assigned before assigned before
conflicts and need to cover conflicts and need to cover conflictsconflicts
and and disrupted pairingsdisrupted pairings
• Reserves needed less if Reserves needed less if recoveryrecovery protects protects
future trips future trips
25 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Scheduling Recurrent TrainingScheduling Recurrent Training
Between planning and operationsBetween planning and operations
Determines conflicts Determines conflicts
• Schedule reserves to cover pairings Schedule reserves to cover pairings
• Schedule deadheads, classes, and Schedule deadheads, classes, and
simulators for continuing qualification simulators for continuing qualification
Mainly feasibility constraints but costsMainly feasibility constraints but costs
• Trips that fall outTrips that fall out
• Instructors to fill in on simulators Instructors to fill in on simulators
26 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Crew Scheduling IssuesCrew Scheduling Issues
Modeling and optimization have been Modeling and optimization have been
successfully applied to:successfully applied to:
• Pairing optimization Pairing optimization
• Bidlines and rosteringBidlines and rostering
The rest of the storyThe rest of the story
• Manpower planning and trainingManpower planning and training
• Reserve crew bidlines and utilizationReserve crew bidlines and utilization
• Operations and recoveryOperations and recovery
27 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
More of the Rest of the StoryMore of the Rest of the Story
Numbers of pilots for future fleets and Numbers of pilots for future fleets and
schedules schedules
Quality of life issues Quality of life issues
Fatigue: circadian rhythm in planning Fatigue: circadian rhythm in planning
and recoveryand recovery
• Weekly patterns of days offWeekly patterns of days off
““Overtime” flying and reserve crewsOvertime” flying and reserve crews
Crew compatibility, cabin crew, weeklyCrew compatibility, cabin crew, weekly
28 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
FatigueFatigue
Research shows shortening the 24-Research shows shortening the 24-hour clock causes fatigue, slower hour clock causes fatigue, slower reactions, and insomnia reactions, and insomnia • Even for domestic fleets due to red-eyesEven for domestic fleets due to red-eyes
• Also tendency for short duty + short restAlso tendency for short duty + short rest
• Jet lag is a familiar but serious problem Jet lag is a familiar but serious problem • Even international business travelers suffer Even international business travelers suffer
insomniainsomnia
Maintaining sleep window in planningMaintaining sleep window in planning• E.g. 9pm - 4 am in pairing and bid linesE.g. 9pm - 4 am in pairing and bid lines
Operations can lead to longer dutiesOperations can lead to longer duties
29 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Robust Scheduling Robust Scheduling
Crew-compatible fleet assignment Crew-compatible fleet assignment • Pure city at small spokesPure city at small spokes
• Helps with crew, maintenance, plane swapsHelps with crew, maintenance, plane swaps
• Critical presence and mid-day breakoutsCritical presence and mid-day breakouts
Crew basesCrew bases• Pure city gives more swapsPure city gives more swaps
• Mainly for overnighting crewsMainly for overnighting crews
Critical presence of crew-compatible Critical presence of crew-compatible fleets at complexesfleets at complexes
• Plane swaps for D3 and crew swaps Plane swaps for D3 and crew swaps
30 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
Solving These ProblemsSolving These Problems
Many, many column LPs and IPsMany, many column LPs and IPs Station decomposition for FAM Station decomposition for FAM Non-negative least squares methods Non-negative least squares methods
• Primal-dual subproblem methodsPrimal-dual subproblem methods• Dual-primal and d-p subproblem Dual-primal and d-p subproblem • Combined objective function methodsCombined objective function methods• Network flow specialized methodNetwork flow specialized method
Use of parallel clusterUse of parallel cluster• MARS code for stochastic problems MARS code for stochastic problems • Parallel SimAir (so far just a dream)Parallel SimAir (so far just a dream)
31 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
SimAir PurposeSimAir Purpose
Allows running different schedules Allows running different schedules
and different recovery algorithms and and different recovery algorithms and
checking performancechecking performance
Allows testing different planning Allows testing different planning
models with different recoverymodels with different recovery
Improvement from better recoveryImprovement from better recovery
• Initial recovery was pushbackInitial recovery was pushback
• Cancel short cycles, reroute planesCancel short cycles, reroute planes
32 IMA Travel and Transportation, Nov 14 2002IMA Travel and Transportation, Nov 14 2002
National University of SingaporeNational University of Singapore
Temasek Project in Air Logistics and Temasek Project in Air Logistics and TransportTransport• Air logistics business process and ITAir logistics business process and IT• Air cargo terminals - efficient operation Air cargo terminals - efficient operation • Multi-commodity flow and cargo flowMulti-commodity flow and cargo flow• Crew scheduling in A-P long-haul Crew scheduling in A-P long-haul
environment environment • Air cargo YM, booking, and trackingAir cargo YM, booking, and tracking• SimAir including passenger and cargo SimAir including passenger and cargo
reroutingrerouting