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An Irregular Flight Scheduling Model and Algorithm under the Uncertainty Theory

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Journal of Applied Mathematics
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The flight scheduling is a real-time optimization problem. Whenever the schedule is disrupted, it will not only cause inconvenience to passenger, but also bring about a large amount of operational losses to airlines. Especially in case an irregular flight happens, the event is unanticipated frequently. In order to obtain an optimal policy in airline operations, this paper presents a model in which the total delay minutes of passengers are considered as the optimization objective through reassigning fleets in response to the irregular flights and which takes into account available resources and the estimated cost of airlines. Owing to the uncertainty of the problem and insufficient data in the decision-making procedure, the traditional modeling tool (probability theory) is abandoned, the uncertainty theory is applied to address the issues, and an uncertain programming model is developed with the chance constraint. This paper also constructs a solution method to solve the model based on the classical Hungarian algorithm under uncertain conditions. Numerical example illustrates that the model and its algorithm are feasible to deal with the issue of irregular flight recovery.
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Hindawi Publishing Corporation
Journal of Applied Mathematics
Volume , Article ID , pages
http://dx.doi.org/.//
Research Article
An Irregular Flight Scheduling Model and Algorithm under
the Uncertainty Theory
Deyi Mou and Wanlin Zhao
Institute of Mathematics for Applications, Civil Aviation University of China, Tianjin 300300, China
Correspondence should be addressed to Deyi Mou; deyimou@hotmail.com
Received  June ; Revised  August ; Accepted  August 
Academic Editor: Zhiwei Gao
Copyright ©  D. Mou and W. Zhao. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
e ight scheduling is a real-time optimization problem. Whenever the schedule is disrupted, it will not only cause inconvenience
to passenger, but also bring about a large amount of operational losses to airlines. Especially in case an irregular ight happens, the
event is unanticipated frequently. In order to obtain an optimal policy in airline operations, this paper presents a model in which
the total delay minutes of passengers are considered as the optimization objective through reassigning eets in response to the
irregular ights and which takes into account available resources and the estimated cost of airlines. Owing to the uncertainty of the
problem and insucient data in the decision-making procedure, the traditional modeling tool (probability theory) is abandoned,
the uncertainty theory is applied to address the issues, and an uncertain programming model is developed with the chance
constraint. is paper also constructs a solution method to solve the model based on the classical Hungarian algorithm under
uncertain conditions. Numerical example illustrates that the model and its algorithm are feasible to deal with the issue of irregular
ight recovery.
1. Introduction
Aschedulewehavemadeisfrequentlycomplexanddynamic,
and uncertainty ttingly characters its intrinsic nature. Vari-
ous unanticipated events will disrupt the system and make the
schedule deviate from its intended course, even make it infea-
sible; furthermore, they will bring about a large quantity of
losses. en, we apply a method of disruption management to
cope with it, to reach our goals while minimizing all the neg-
ative impact caused by disruptions and to get back on track
in a timely manner while eectively using available resources.
e disruption management refers to the real time dynamic
revision of an operational plan when a disruption occurs.
is is especially important in situations where an operational
plan has to be published in advance, and its execution is
subject to severe random disruptions. When a published
operational plan is revised, there will be some deviation cost
associated with the transition from the original plan to the
new plan. To reduce such deviation cost, it is essential to take
them into account when generating the new plan. Disruption
management is a real-time practice and oen requires a quick
solution when a disruption occurs. e original planning
problem usually is regarded as a one-time eort, so it is prac-
tically acceptable if generating an optimal operational plan
takes a dozen of minutes or hours, or even longer. However,
when a disruption occurs, it is critical to immediately provide
a resolution to the responsible personnel. erefore, real-time
optimization techniques are very important.
In the area of transportation network, the schedule is
not frequently executed according to the original plan; the
system is oen disturbed because of uncertainties, time
delays, stochastic perturbations and so on. It is dicult to
deal with the situations. So, the complex dynamic systems are
raisedbyGaoetal.[] in many varieties, including the areas
of transportation networks, energy generation, storage and
distribution, ecosystems, gene regulation and health delivery,
safety and security systems, and telecommunications. ey
also present various mathematical methods and techniques
to discuss the issues.
Airlines spend a great deal of eorts developing ight
schedules for each of their eets, and the daily operations of
an airline are strictly based on a predetermined ight sched-
ule. So, we know how important the eet assignment is. But
there are many uncertain factors having eect on the ights,
Journal of Applied Mathematics
such as bad weather, aircra failure, and airline trac control.
When the ight schedule is disrupted, a deviation from the
ight schedule causes not only inconvenience to passenger,
butalsoalargeamountofoperationalcostbecausetheairline
has to make a new ight schedule that should satisfy all above
constraints. So, the recovery of irregular ights faced by all
airlines in the world is important and dicult to solve.
In USA, Delta Airline summed up , irregular ights,
which aected ,, passengers and caused  million
of losses (not including satisfaction losses of passengers).
Each irregular ight caused losses up to more than ,
on average (not including losses to the passengers because of
delays). In China, the domestic three major airlines executed
,, ights, but there were , irregular ights, and
therateofirregularightwas.%in.Inthesameyear,
the domestic airlines of small and medium sized had ,
ights, and , were irregular ights; the rate of irregular
ight was up to .%. Hence, the irregular ights brought
a large amount of losses to airlines and inconvenience to
passenger in actual life.
Due to the complexity of irregular ight scheduling prob-
lem, it is impossible for airlines to optimize existing resources
relying on experience. e problem of searching fast and
ecient algorithm and soware has not been solved [].
en Teodorovi´
candGuberini
´
c[] proposed a branch and
bound method to minimize total delay minutes of passengers.
Teodorobic and Stojkovic [] raised dynamic programming
model based on principle of lexicographic optimization,
in order to minimize the cancelled ights and the total
delay minutes of passengers. Jarrah et al. []introducedtwo
separate models to minimize delay minutes and cancellations,
respectively, solved by critical path method (CPD). us, the
models were not able to consider the trade-o between delay
and cancellation. Gang []constructedatwo-commodities
network ow model without solving method. Yan and Yang
[] formulated a model to minimize the duration of time
in which the ight scheduling was disrupted. Arg¨
uello et al.
[,] presented resource allocation path ow model for eet
assignment; the model had clear ideas describing the essence
of eet assignment, but it was dicult to solve it. e period
network optimization model about ight operations recovery
could be found in Bard et al. [], and it transformed the
aircra routing problem to a network ow model depend-
ing on discrete-time. Bratu and Barnhart []introduced
a model of ight recovery and algorithm, when irregular
ight happened, considering simultaneously aircra, crew,
and passengers, to decide whether to cancel the ight or
not; the aim was to minimize the sum of total operation
cost of interconnection, cost of passengers, and canceling
cost. e objective function wished to search the trade-o
point between each cost. e essence of above models was to
construct ight leg and cancelled ight or not and select the
minimum cost of the program. But how to generate feasible
ight routes and calculate the cost of each route were dicult.
ere was not a paper which found the exact optimal solution
by solving model directly for airlines up to now.
During the period of irregular ights, we cannot optimize
all situations, and the reasons resulting to irregular ights are
frequently uncertainty. For the decision making of uncertain
problem, Kouvelis and Yu [] described robust discrete
optimization to deal with decision making in environment of
signicant data uncertainty. Matsveichuk et al. []dealt
with the ow-shop minimum-length scheduling problem
with jobs processed on two machines when processing time
is uncertain. Reference [] presented minimal (maximal)
cardinality of a -solution generated by Johnsons algorithm
tosolvetheproblemabove;however,formostgeneralizations
of the two-machine ow-shop problem, the existence of
polynomial algorithms is unlikely. For the duration of each
irregular ight, we cannot analyze it without enough data,
and it is not feasible to be dealt with by using stochastic pro-
gramming. But we can invite experts to give the approximate
duration of delay time and its uncertainty distribution. en,
we can apply uncertainty theory with a great premise. Here
we will apply uncertainty theory to component model with
uncertain programming and provide a stepwise algorithm for
themodel.Inthispaper,wesearchforminimizingthetotal
delay minutes of passengers under the constraint of estimated
cost. Next, this paper gives introduction of uncertainty theory
and model, the method of constructing the model, the
algorithm of solving model, and numerical example for the
model. At last, we provide some future directions.
2. Preliminaries
In this section, some basic denitions are introduced, and
the arithmetic operations of uncertain theory which needed
throughout this paper are presented.
Denition 1 (Liu []). Let Γbe a nonempty set and La-
algebra over Γ. Each element Λ∈Lis called an event. e
set function Mis called an uncertain measure if it satises the
following four axioms.
1(normality). M{Γ}=1;
2(monotonicity). M1}≤M2}when-
ever Λ1⊂Λ2;
3(self-duality). M{Λ}+M𝑐}=1for any
event Λ;
4(countable subadditivity). For every count-
able sequence of events 𝑖},wehave
M
𝑖=1Λ𝑖≤
𝑖=1
MΛ𝑖. ()
Denition 2 (Liu []). Let Γbe a nonempty set, La-
algebra over Γ,andMan uncertain measure. en the triple
(Γ,L,M)is called on uncertainty space.
Denition 3 (Liu []). An uncertain variable 𝜉is a measur-
able function from the uncertainty space (Γ,L,M)to the set
of real numbers; that is, for any Borel set Bof real numbers,
the set {𝜉B}=∈Γ|∈B()
is an event.
Journal of Applied Mathematics
For a sequence of uncertain variables 1,2,...,𝑛and a
measurable function ,Liu[]provedthat
𝜉=1,2,...,𝑛()
dened as ()=(1(),2(),...,𝑛()),forall∈Γis
also an uncertain variable. In order to describe an uncertain
variable, a concept of uncertainty distribution is introduced
as follows.
Denition 4 (Liu []). e uncertainty distribution Φof an
uncertain variable 𝜉is dened by
Φ(x)=M{𝜉x}()
for any real number x.
Peng and Li []provedthatafunctionΦ:R[0,1]
is an uncertainty distribution if and only if it is a monotone
increasing function unless Φ()0or Φ()1.einverse
function Φ−1 is called the inverse uncertainty distribution of
𝜉. Inverse uncertainty distribution is an important tool in the
operation of uncertain variables.
eorem 5 (Liu []). Let 1,2,...,𝑛be independent
uncertain variables with regular uncertainty distributions
Φ1,Φ2,...,Φ𝑛,respectively.If(1,2,...,𝑛)is an increas-
ing function with respect to 1,2,...,𝑚and decreasing with
respect to 𝑚+1,𝑚+2,...,𝑛,then
𝜉=1,2,...,𝑛()
is an uncertain variable with inverse uncertainty distribution
Ψ−1 ()=Φ−1
1(),Φ−1
2(),...,Φ−1
𝑚(),
Φ−1
𝑚+1 (1−),...,Φ−1
𝑛(1−). ()
Expected value is the average of an uncertain variable in
the sense of uncertain measure. It is an important index to
rank uncertain variables.
Denition 6 (Liu []). Let 𝜉be an uncertain variable. en
the expected value of 𝜉is dened by
[𝜉]=
0
M{𝜉≥}0
−∞
M{𝜉≤} ()
provided that at least one of the two integrals is nite.
In order to calculate the expected value via inverse
uncertainty distribution, Liu []provedthat
[𝜉]=1
0Φ−1
1(),...,Φ−1
𝑚(),
Φ−1
𝑚+1 (1−),...,Φ−1
𝑛(1−)()
under the condition described in eorem . Generally, the
expected value operator has no linearity property for
arbitrary uncertain variables. But, for independent uncertain
variables 𝜉and 𝜂with nite expected values, we have
𝜉+𝜂=[𝜉]+𝜂()
for any real numbers and .
eorem 7 (Liu []). Assume the objective function (x,1,
2,...,𝑛)is strictly increasing with respect to 1,2,...,𝑚
and strictly decreasing with respect to 𝑚+1,𝑚+2,...,𝑛.If1,
2,...,𝑛are independent uncertain variables with uncertainty
distribution Φ12,...,Φ𝑛, respectively, then the expected
objective function x,1,2,...,𝑛 ()
is equal to
1
0x,Φ−1
1(),...,Φ−1
𝑚(),
Φ−1
𝑚+1 (1−),...,Φ−1
𝑛(1−). ()
eorem 8 (Liu []). Assume (x,1,2,...,𝑛)is strictly
increasing with respect to 1,2,...,𝑚and strictly decreasing
with respect to 𝑚+1,𝑚+2,...,𝑛,and𝑗(x,1,2,...,𝑛)are
strictly increasing with respect to 1,2,...,𝑘and strictly
decreasing with respect to 𝑘+1,𝑘+2,...,𝑛,for=1,2,...,.
If 1,2,...,𝑛are independent uncertain variables with
uncertainty distributions Φ12,...,Φ𝑛, respectively, then the
uncertain programming
min
𝑥x,1,2,...,𝑛,
s.t. M𝑗x,1,2,...,𝑛≤≥𝑗, =1,2,...,,
()
is equivalent to the crisp mathematical programming
min
𝑥1
0x,Φ−1
1(),...,Φ−1
𝑚(),
Φ𝑚+1−1 (1−),...,Φ−1
𝑛(1−),
s.t. 𝑗x,Φ−1
1𝑗,...,Φ−1
𝑘𝑗,Φ−1
𝑘+1 1𝑗,...,
Φ−1
𝑛1𝑗, =1,2,...,. ()
3. Problem Description
For airlines, irregular ights are not expected but they are
inevitable frequently owing to objective factors in practice.
So, each airline has its own methods to deal with the issue.
At present, the irregular ight recovery is a complex and
huge project to airlines. Generally speaking, the Airline
Journal of Applied Mathematics
Flights
Cancel
Homeplate
Make decisions for flights aected
From other
eld
Preliminary
scheme
End
Real-time situation
Adjust flight
schedule or not
Ye s
Ye s
Ye s
Ye s
Delays happened
No
No
No
No Adjust or
not
Cancel or
not
postpone
Homeplate or
not
Ferry
F : Flow chart of procedure.
Operational Control (AOC) of each airline takes the
following procedure for dealing with the irregular ights.
Step . Maintenance Control Center (MCC) reports delays to
AOC.
Step . AOC gets detailed information from relevant depart-
ments.
Step . AOC gives the expected minutes of ight delay
according to the information.
Step . AOC makes a decision whether the rst delay ight
cancels or postpones.
Step . Making decisions to the following ights.
Step . AOC always pays attention to real-time situations and
whether the decision will be to remake or not based on real-
time changes.
e ow chart of procedure is shown in Figure .From
this ow chart, we can get that it is dicult to make a suitable
and reasonable schedule. In this paper, we resolve the irregu-
lar ight problem about eet reassignment based on the ow
chart. When irregular ights happen, the durations of delay
time only are predicted through the data given by experts,
in order to help the decision makers to reassign eets better.
During the period of delay time, the airlines can postpone
the ights, minimize the delay minutes or delay cost by
reassigning and canceling ights, or minimize the total delay
minutes under the constraint of estimated cost by reassigning
ights; in a word, the aim is to serve the passengers better.
Tobia s [ ] presented a tabu search and a simulated
annealing approach to the ight perturbation problem and
used a tree-search algorithm to nd new schedules for
airlines,anditcouldbesuccessfullyusedtosolvethe
ight perturbation problem. Gao et al. []putforwarda
greedy simulated annealing algorithm which integrated the
characteristics of GRASP and simulated annealing algorithm,
and the algorithm was able to solve large-scale irregular ight
schedule recovery. Xiuli []introducedastepwise-delay
algorithm to research irregular ight problem. She solved the
problem from the delay cost and delay minutes, respectively.
In the paper, the delay minutes and delay cost were set down
as constant values. From comparing the two methods, Xiuli
got the result that to construct the model with delay minutes
obtained successful results.
But there are not enough data of irregular ights to
analyze; the data is dicult to deal with under the stochastic
condition. In actual situations, we cannot obtain enough data
to analyze, so, in this paper, we treat the duration of delay
time of aircra as an uncertain variable during the period
of irregular ights happening, and its distribution is given by
experts. Under the constraints of estimated cost and aircra
assignment model, the objective function is to minimize the
total delay minutes of passengers relying on irregular ights.
enwesolvethemodelandgetthesolution.
4. Model Development
In actual situations, the factors which cause irregular ights
are uncontrolled frequently. Especially when the weather is
bad and aircra failure happens, the durations of bad weather
and aircra failure cannot be predicted exactly because of
lacking enough data under stochastic condition. In this
model, we consider the delay time as an uncertain variable,
and its uncertainty distribution is given by experts.
Firstly, we introduce the following notations to present
the mathematical formulation throughout the remainder of
this paper.
Indices, Sets, and Parameters
: index for set of ights
: index for set of airports
: index for set of types of aircras
:setoftypesofaircras
:setofights
: set of airports
: set of available aircras
𝑖:readytimeofaircra
𝑑
𝑓: planning departure time of ight
𝑎
𝑓: planning arrival time of ight
𝑓
𝑖: uncertain delay time of ight executed by type
of aircra, 𝑓
𝑖∼𝑖(),∈
𝑏
𝑓,𝑒
𝑓: reservation number of business and economy
class in ight
Journal of Applied Mathematics
𝑏
𝑓,𝑒
𝑓: fare of a ticket of business and economy class
in ight
𝑓: total reservations of ight
: disappointment rate of passengers
V:lossesvalueofpassengersperminute
𝑓
𝑖: delay loss of ight executed by aircra ,𝑓
𝑖=
𝑓𝑓
𝑖,when𝑓
𝑖>0,or=
𝑓: cost of canceling ight
:airportusagechargeperminute
: cost of depreciation of aircra per minute
𝑓
𝑖: delay cost of ight executed by aircra
𝑓
0: estimated cost of ight
𝑓=(𝑓
𝑖),0=(𝑓
0)
0: condence level
:weightofcostofcancellingight
𝑓
𝑖: binary variable, =  if ight is executed by
aircra and  otherwise
𝑓: binary variable, =  if ight is canceled and 
otherwise.
Xiuli []presentedtwomodelstodealwiththeirregular
ight. eir objective functions were to minimize delay
minutes and total delay cost:
min
𝑓∈𝐹
𝑖∈𝐴𝑓
𝑖𝑓
𝑖+
𝑓∈𝐹𝑓𝑓,
min 𝑓x,𝑓. ()
In our paper, we construct the model under the basis
ofthetwomodels,andintegratethemtoone.Next,based
on the analysis of the decision making process, we integrate
the estimated cost and the total delay minutes of passengers
model and propose the following model:
min
𝑓∈𝐹
𝑖∈𝐴𝑓
𝑖𝑓
𝑖+
𝑓∈𝐹𝑓𝑓
,()
s.t.M𝑓x,𝑓<0≥0,()
𝑖∈𝐴𝑓
𝑖+𝑓=1, ∀∈,,∈, ()
𝑓
𝑖=𝑓
𝑖𝑒
𝑓×𝑒
𝑓+𝑏
𝑓×𝑏
𝑓×
++𝑓
𝑖+𝑓𝑓,
𝑓=1−𝑓
𝑖,()
𝑓∈𝐹𝑓
𝑖≤1, ∀∈, ()
𝑓
𝑖{0,1},
𝑓{0,1}.()
In the model, () is the objective function of minimizing
the total delay minutes of passengers, the former is the delay
minutes depending on the irregular ights, the latter is the
equivalent delay minutes relying on ights cancelled; ()is
the constraint of estimated cost; () states a ight is either
own once by an aircra or canceled; ()isthedelaycostof
ight executed by aircra ;() assigns no more than one
aircra to execute ight ;and() is the integer constraint
of -.
e model is to minimize the total delay minutes of
passengers under the estimated cost. Generally speaking, we
need to recur to intelligent algorithm to solve the model; it is
ahugeprojecttogetitssolution[].
But, it will be much easier under the uncertainty theory
to deal with the problem. Note that 𝑓(x,𝑓)is strictly
increasing with respect to 𝑓
𝑖(=1,2,...,),and𝑓
1,𝑓
2,...,𝑓
𝑛
are independent uncertain variables with uncertainty distri-
butions 𝑓
𝑖∼𝑖()(=1,2,...,), respectively. According
to eorem ,theabovemodelwillbeequivalenttothe
following deterministic model:
min
𝑓∈𝐹
𝑖∈𝐴 𝑓
𝑖𝑓1
0−1
𝑖𝑓
𝑖,
+
𝑓∈𝐹𝑓𝑓
,
s.t.Φ−1 x,0<0,
𝑖∈𝐴𝑑𝑖
𝑓𝑎𝑖
𝑓𝑓
𝑖+𝑓=1, ∀∈,,∈,
𝑓
𝑖=𝑓
𝑖𝑒
𝑓×𝑒
𝑓+𝑏
𝑓×𝑏
𝑓×
+𝑓
𝑖+𝑓𝑓, 𝑓=1−𝑓
𝑖,
𝑓∈𝐹𝑓
𝑖≤1, ∀∈,
𝑓
𝑖{0,1},
𝑓{0,1}.
()
In this model, the objective function is to minimize the
expected total delay minutes of passengers, and the estimated
cost is treated as a chance constraint, where
Φ−1 (x,)=−1
𝑖𝑓
𝑖,. ()
5. Solution Method and Complexity
5.1. Solution Method. In the model, there is an objective
function, but it contains two kinds of decision variables 𝑓
𝑖
and 𝑓.Tosolvethemodel,wemakeuseofastepwise-delay
algorithm.eprocedureofsolutionisasfollows.
Step 1. Basedontheinformationpostponed,gettingthe
timetable of ights as .
Journal of Applied Mathematics
T : Estimated cost.

0/RMB
xx 
xx 
xx 
xx 
xx 
xx 
xx 
Total:  ,
Step 2. Sorting the delay ights depending on original depar-
ture time from the timetable of delay ight, and searching the
rst airport where delay happened. During the delay period,
we retrieve the serial number of aircras through the airport,
andnotethemdowninthetable.
Step 3. Finding available aircras in the delay airport, a time
permutation table is built via the constraints, Φ−1(x,)<
0. e delay minutes are replaced by [𝑓
𝑖];thenwecanget
the following: 1∗ 2∗ ⋅∗
=𝑓
𝑖=1
2
.
.
.
𝑛
1
12
1⋅⋅⋅𝑛
1
1
22
2⋅⋅⋅𝑛
2
.
.
..
.
..
.
..
.
.
1
𝑛2
𝑛⋅⋅⋅𝑛
𝑛
.()
Step 4. For , we use Hungarian algorithm to reassign avail-
able aircra and get the new timetable:
= 1∗ 2∗ ⋅∗
1
2
.
.
.
𝑛10.
.
.
000.
.
.
1⋅⋅⋅
⋅⋅⋅
.
.
.
⋅⋅⋅ 00.
.
.
0.()
Step 5. Renewing the , the relevant aircra assignment
is replaced by the consequence from Step ;thenturnto
Step , and steps are repeated until there are no delay ights
or optimal ights. en the results are put out.
5.2. Complexity. For one delay airport, we use Hungarian
algorithm to reassign eets in that the complexity is (2).
When the number of delay airports is ,thealgorithmwill
be iterated in each airport, so that the total complexity is
(2)whichisapolynomial.Soitisafeasiblemethodin
applications.
6. Illustrative Example and
Computational Result
In order to test the model and the solution algorithms
applied in the actual situation, we perform numerical tests
based on the domestic operation department with reasonable
assumptions.
Wesupposethattheairlinehasthehubairportof1;the
ights are 1to 2,1to 3,and2to 3. Its types of aircras are
310and 737. Assume that the delay minutes of irregular
ights are linear uncertain variables, and their distributions
are as follows:
1L(10:40,11:20),
2L(15:50,16:30),
3L(12:10,12:50),
4L(15:10,15:50),
5L(16:20,17:00).()
e disappointment rate of passengers =0.07𝑓
𝑖/60+
0.4. e delay minutes of passengers are as follows:
𝑓
𝑖=
0.3𝑓×𝑓
𝑖
60 𝑓
𝑖[0,60),
0.5𝑓×𝑓
𝑖
60 𝑓
𝑖[60,120),
0.7𝑓×𝑓
𝑖
60 𝑓
𝑖[120,240),
0.9𝑓×𝑓
𝑖
60 𝑓
𝑖[240,).
()
We assume that the constraint of estimated cost is shown
in Table .
At last, we assume that the timetable is shown in Table  .
e predetermined condence level 0=0.9.
en, we use the algorithm and get the optimal solution
shown in Table .
Comparing Tables ,and ,wecangettheoptimal
solution through the model. From Tabl e  ,wecanseethat
the cost is , RMB under the constraint of , RMB,
and the ight delay time is ten minutes less than Tab l e  .
Based on Tables and , there is a great dierence in the
total delay minutes of passengers. Ta b l e  is about . times as
many as Tab l e  , and there is not a cancelled ight in Tab l e  .
So the reassignment of Table  is much better than Table .
e example shows that the model and algorithm can get a
method of ight recovery better.
7. Conclusions and Future Directions
e irregular ights always happen in actual situations; in
order to deal with the issue, in this paper, we developed a
model for eet reassignment based on uncertain program-
ming during the period of irregular ights and presented a
stepwise optimization method strategy based on Hungarian
Journal of Applied Mathematics
T : Timetable postponed.

𝑑
𝑓𝑎
𝑓𝑖(𝑓
𝑖)/minute 𝑏
𝑓/𝑏
𝑓𝑒
𝑓/𝑒
𝑓𝑑𝑖
𝑓𝑎𝑖
𝑓
/ xx : : : / / 12
/ xx : : : / / 21
/ xx : : 1 / / 13
/ xx : : 2 / / 31
/ xx : : 3 / / 12
/ xx : : 4 / / 21
/ xx : : : Canceled / / 13
/ xx : : : Canceled / / 31
/ xx : : : / / 31
/ xx : : 5 / / 12
Total delay minutes of ights: ; canceled: ; value of objective function: ,.
T : Timetable aer reassigning.

𝑑
𝑓𝑎
𝑓𝑖(𝑓
𝑖)/minute 𝑑𝑖
𝑓𝑎𝑖
𝑓
/ xx : : :  13
/ xx : : :  31
/ xx : : :  13
/ xx : : :  31
/ xx : : : 31
/ xx : : :  12
/ xx : : : 12
/ xx : : : 21
/ xx : : :  12
/ xx : : :  21
Total delay minutes of ights: ;, canceled: ; value of objective function: ,.
Total cost of ights delay: , RMB.
algorithm to solve the problem. Compared with the tradi-
tional model, we introduce an uncertain variable into the
model and construct it based on uncertain programming.
Weconsiderthedelayminutesasuncertainvariableswith
their uncertainty distributions given by experts. We con-
struct a stepwise optimization method based on Hungarian
algorithm to solve the model. From results of the numerical
example, the total delay minutes of passengers are declined
extensively, and we can get that the model and algorithm are
feasible to deal with the issue of irregular ights.
A major contribution of this paper is that we provide
a comprehensive framework for eet reassignment during
the period of irregular ights happen. Much work still needs
to be done to improve on the current framework. Partially,
we believe future research can be conducted on an integral
framework of eet reassignment and crew schedule recovery.
us approaching the irregular ights problem is more
systematical. Furthermore, considering actual situations, we
canalsoconstructanintegraluncertainandstochasticmodel;
thus, dealing with the issue of irregular ights is more
comprehensive.
Acknowledgments
is work was supported by the Fundamental Research
Funds for the Central Universities (Grant ZXHC).
e authors would like to thank the anonymous referees for
useful suggestions and comments on the earlier dra of this
paper.
References
[] Z. Gao, D. Kong , and C. Gao, “Modeling and control of complex
dynamic systems: applied mathematical aspects,Journal of
Applied Mathematics, vol. , Article ID ,  pages, .
[] A. Mathur and J. P. Clarke, How Healthy Is Your Operation,
AGIFORS, .
[] D. Teodorovi´
c and S. Guberini´
c, “Optimal dispatching strategy
on an airline network aer a schedule perturbation,European
Journal of Operational Research,vol.,no.,pp.,.
[] D. Teodorovic and G. Stojkovic, “Model to reduce airline
schedule disturbances,Journal of Transportation Engineering,
vol. , no. , pp. –, .
[]A.I.Z.Jarrah,G.Yu,N.Krishnamurthy,andA.Rakshit,
“Decision support framework forairline ight cancellations and
delays,Transportation Science,vol.,no.,pp.,.
[] Y. Gang, “An optimization model for airlines’ irregular oper-
ations control,” in Proceedings of the International Symposium
on Optimization Applications in Management and Engineering,
.
[] S. Yan and D. Yang, “A decision support framework for handling
schedule perturbation,Transportation Research B,vol.,no.
, pp. –, .
Journal of Applied Mathematics
[] M. F. Arg¨
uello,J.F.Bard,andG.Yu,“AGRASPforaircra
routing in response to groundings and delays,Journal of
Combinatorial Optimization,vol.,no.,pp.,.
[] M. F. Arg¨
uello,J.F.Bard,andG.Yu,“Modelsandmethods
for managing airline irregular operations,International Series
in Operations Research & Management Science,vol.,pp.,
.
[] J.F.Bard,G.Yu,andM.F.Arg
¨
uello, “Optimizing aircra rout-
ings in response to groundings and delays,IIE Transactions,
vol.,no.,pp.,.
[] S. Bratu and C. Barnhart, “Flight operations recovery: new
approaches considering passenger recovery,Journal of Schedul-
ing,vol.,no.,pp.,.
[] P. Kouvelis and G. Yu, Robust Discrete Optimization and Its
Applications, vol. , Kluwer Academic, Boston, Mass, USA,
.
[] N.Matsveichuk,S.Yuri,andW.Frank,“Pertialjob-Oorderfor
solving the two-machine ow-shop minimum-length problem
with uncertain processing times,Information Control Problems
in Manufacturing,vol.,no.,pp.,.
[] N. M. Matsveichuk, Y. N. Sotskov, and F. Werner, “e dom-
inance digraph as a solution to the two-machine ow-shop
problem with interval processing times,Optimization,vol.,
no. , pp. –, .
[] C.T.Ng,N.M.Matsveichuk,Y.N.Sotskov,andT.C.E.Cheng,
“Two-machine ow-shop minimum-length scheduling with
interval processing times,Asia-Pacic Journal of Operational
Research,vol.,no.,pp.,.
[] B. Liu, eory and Practice of Uncertain Programming,Springer,
Berlin, Germany, nd edition, .
[] B. Liu, Uncertainty eory, th edition, .
[] J. Peng and S. G. Li, “Spanning tree problem of uncertain
network,http://orsc.edu.cn/online/.pdf.
[] T. Andersson, “Solving the ight perturbation problem with
meta heuristics,Journal of Heuristics,vol.,no.-,pp.,
.
[] Q. Gao, X. Tang, and J. Zhu, “Research on greedy simulated
annealing algorithm for irregular ight schedule recovery
model,” in Advances in Grey Systems Research, pp. –,
Springer, Berlin, Germany, .
[] Z. Xiuli, Research on modeling and algorithm of airline irregular
recovery [Ph.D. thesis], Nanjing University of Aeronautics and
Astronautics, Nanjing, China, .
[] J. D. Petersen, G. S¨
olveling, J.-P. Clarke, E. L. Johnson, and
S. Shebalov, “An optimization approach to airline integrated
recovery,Transportation Science,vol.,no.,pp.,
.
... In Table 1, 'network' refers to the network type for aircraft recovery model construction: connection network (CN), time space network (TN), and time band network (TBN). The detailed [31] NA NO YES YES NO Multi Single Nonlinear Operation, delay, passenger cost Babić et al. [32] NA YES YES YES NO Multi Single Nonlinear Max revenue minus operational and disturbance costs Liu et al. [30] NA NO YES YES NO Single Multi Nonlinear Delay time, duty swap, variance of flight delay time, number of delayed flight, number of long-delayed flight Gao et al. [36] NA NO YES NO NO Single Multi Nonlinear Weighted flight delay time Mou et al. [37] NA YES YES YES NO Multi Multi Nonlinear Delay minutes, delay, and cancellation cost Aktürk et al. [38] CN NO YES YES YES Multi Single Conic IP Delay, deadhead, additional fuel and carbon emission, passengers spilled cost Vos et al. [17] TN YES YES YES NO Single Single LP Operation, delay, cancellation, aircraft ground cost Guimarans et al. [33] NA NO YES YES NO Single Single CP Delay time Xu et al. [22] TBN YES YES YES NO Single Single IP Delay, cancellation cost Hu et al. [24] CN Review of airline disruption management network representation has been issued in Clausen et al. [8] . 'Cancel', 'delay', 'aircraft swap', 'fleet', and 'cruise speed' refer to whether the paper considers the recovery options of flight cancellation, flight delay, aircraft swapping, swapping between multiple fleet types, and cruise speed control, respectively. ...
... Gao et al. [36] NA NO YES Polynomial algorithm Generated 4 8 NA Mou et al. [37] Linear NO NO Polynomial algorithm Generated 5 10 NA Aktürk et al. [38] Nonlinear YES YES CPLEX An airline in the US 60 207 248.4 Vos et al. [17] Nonlinear YES NO Selection algorithm Kenya Airways 43 NA 600 Guimarans et al. [33] NA NO NO Large neighbourhood search RL 48 294 205.514 Xu et al. [22] Linear NO NO CPLEX RL 60 254 949.7 Hu et al. [24] Linear NO NO Heuristic based on ε-constraints and neighbourhood search A major Chinese airline 104 401 1200 ...
... Although the aircraft recovery problem has been proven NPhard [35] , some studies still prefer to analyze optimization characteristics and design polynomial algorithms for some special cases of the problem. Gao et al. [36] focus on flight rescheduling under large-scale flight delays considering flight delays and flight cancellations rather than flight swaps between different aircraft routings. Then, a polynomial algorithm is designed to obtain the optimal solution for the flight rescheduling problem. ...
Article
Full-text available
This paper conducts a thorough review of airline disruption management between 2010 and 2024. Unlike previous review papers, the present paper analyses the research on airline disruption management in three ways. One is to perform a statistical analysis of these papers based on the journal distribution, number of papers by year, and types of recovery resources. The second is to categorize integrated recovery methods based on the degree of integration of the resources during the recovery process: the aircraft and crew, the aircraft and passengers, and all three resources. The last way is to study the research findings based on statistical analysis and perform future research direction identification in the areas of problems, models, and solution approaches. Further, with the increasing complexity of actual demands, integrated flight disruption recovery considering multiple factors such as aircraft, crew, and passengers has become a research hotspot in recent years. For further research, we can delve deeper into issues from both practical circumstances and theoretical extensions. At the model level, more detailed characterizations are needed, along with more efficient solution methods to accommodate increasingly complex problems.
... Based on the procedure in Fig. 1, it is rather difficult to form a comprehensive schedule. Mou and Zhou [15] had used the Hungarian algorithm in solving model that has the application of uncertainty theory. Hence, total delay minutes will be minimized based on a certain amount of cost. ...
... They also proposed that a future research on fleet reassignment, crew schedule recovery, integral uncertain and stochastic model. These proposed ideas aim to make the approach for flight delay more comprehensive and systematic [15]. By detecting the irregular flight at the very beginning certainly allow more time to predict possible flight delay and mitigation step can be undertaken by the airline company to handle such situation systematically. ...
... Flow chart of flight delay procedure by Airline Operational Control (AOC)[15]. ...
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This paper is a short review of metaheuristic algorithm applications in the airline industry. The purpose of these applications is to optimize the flight operation, especially during flight delay situation. Big data in the flight industry play an important role in predictive as well as prescriptive analysis. Usage of historical flight data enable model building using a metaheuristic algorithm to find a better solution in dealing with flight delay. Optimization on flight route, airlines recovery problem, crew rescheduling and passenger centric strategy will be further discussed in this paper as well. Previous related works on each aspect are reviewed to have a better understanding of the available solutions. Some recommendations are also suggested for future improvement, based on the review.
... In the last stage, a large change to the schedule was made to see if better solutions would be obtained. Recently, Mou and Zhao (2013) aimed to minimize the total delay minutes of passengers, as its main objective, by reassigning aircraft to disrupted flights, meanwhile minimizing the total cost induced. There were also some conference papers in this area, such as by Waheed and Makhlouf (2012), Makhlouf and Waheed (2012), Chan et al. (2013), and Le et al. (2013). ...
... Integer programming Gao et al. (2012) Flights re-scheduling Polynomial algorithm Petersen et al. (2012) A fully integrated recovery model Column generation Waheed and Makhlouf (2012) Flight amalgamation Multi-objective genetic algorithm Wu and Le (2012) Aircraft routing Iterative tree growing with node combination method Jeng (2012) Short haul flights Inequality-based multi-objective genetic algorithm Li and Wallace (2012) Continuous time aircraft routing model Linear programming with relaxation Waheed and Makhlouf (2012) Disruption of flights Multi-objective genetic algorithm Castro et al. Impact of disruptions to passengers' itineraries Genetic algorithm Le et al. (2013) Minimize flight delay cost Genetic algorithm Mou and Zhao (2013) Optimizing total delay minutes of passengers Hungarian algorithm Xiong and Hansen (2013) Flight cancellation Piecewise linear programming Kontogiannis and Malakis (2013) Discussion of lost control situations in air traffic control Control strategies Le et al. (2013) Modelling of recovery network Column generation Jozefowiez et al. (2013) Passenger reassignment Heuristic Aktürk et al. (2014) Recovery by cruise speed Conic integer programming Lei and Zhao (2014) Flight cancellation and delays Column generation algorithm Sinclair et al. (2014) Creating new aircraft routes and passenger itineraries Large neighborhood search Heuristic Table IV. 260 minutes buffer times in the schedule, departure delays can be reduced by 30 per cent. ...
Article
Purpose – The purpose of this paper is to carry out a comprehensive review for state-of-the-art works in disruption risk management of express logistics mainly supported by air-transportation. The authors aim to suggest some new research directions and insights for express logistics practitioners to develop more robust planning in air-transportation. Design/methodology/approach – The authors mainly confined the research to papers published over the last two decades. The search process was conducted in two dimensions: horizontal and vertical. In the horizontal dimension, attention was paid to the evolution of disruption management across the timeline. In the vertical dimension, different foci and strategies of disruption management are employed to distinguish each article. Three keywords were used in the full text query: “Disruption management”, “Air transportation”, and “Airline Operations” in all database searches listed above. Duplications due to database overlap, articles other than those from academic journals, and papers in languages other than English were discarded. Findings – A total of 98 articles were studied. The authors categorized the papers into two broad categories: Reactive Recovery, and Proactive Planning. In addition, based on the problem characteristics and their application scenarios, a total of 11 sub-categories in reactive recovery and nine sub-categories in proactive planning were further identified. From the analysis, the authors identified some new categories in the air-transportation recovery. In addition, by analyzing the papers in robust planning, according to the problem characteristics and the state-of-the-art research in recovery problems, the authors proposed four new research directions to enhance the reliability and robustness of air-transportation express logistics. Research limitations/implications – This study provided a comprehensive and feasible taxonomy of disruption risk management. The classification scheme was based on the problem characteristics and the application scenarios, rather than the algorithms. One advantage of this scheme is that it enables an in-depth classification of the problem, that is, sub-categories of each class can be revealed, which provides a much wider and clearer horizon to the scientific progress in this area. This helps researchers to reveal the problem’s nature and to identify the future directions more systematically. The suggestions for future research directions also point out some critical research gaps and opportunities. Practical implications – This study summarized various reasons which account for the disruption in air-transportation. In addition, the authors suggested various considerations for express logistics practitioners to enhance logistics network reliability and efficiency. Originality/value – There are various classification schemes in the literature to categorize disruption management. Using different algorithms (e.g. exact algorithm, heuristics, meta-heuristics) and distinct characteristics of the problem elements (e.g. aircraft, crew, passengers, etc.) are the most common schemes in previous efforts to produce a disruption management classification scheme. However, the authors herein attempted to focus on the problem nature and the application perspective of disruption management. The classification scheme is hence novel and significant.
... They employed the SERVQUAL model to construct an evaluation index system for the service recovery quality of flight delays, performed a comprehensive assessment of service recovery quality, and utilized a service quality matrix to determine priority improvement indices [15]. Additionally, many scholars have delved into the analysis of flight delay conditions [16]. However, the outbreak of novel coronavirus pneumonia presented a dramatic challenge to the adjustment of irregular flight scheduling. ...
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The novel coronavirus outbreak has significantly heightened environmental costs and operational challenges for civil aviation airlines, prompting emergency airport closures in affected regions and a substantial decline in ridership. The consequential need to reassess, delay, or cancel flight itineraries has led to disruptions at airports, amplifying the risk of disease transmission. In response, this paper proposes a spatial approach to efficiently address pandemic spread in the civil aviation network. The methodology prioritizes the use of a static gravity model for calculating route-specific infection pressures, enabling strategic flight rescheduling to control infection levels at airports (nodes) and among airlines (edges). Temporally, this study considers intervals between takeoffs and landings to minimize crowd gatherings, mitigating the novel coronavirus transmission rate. By constructing a discrete space–time network for irregular flights, this research generates a viable set of routes for aircraft operating in special circumstances, minimizing both route-specific infection pressures and operational costs for airlines. Remarkably, the introduced method demonstrates substantial savings, reaching almost 53.4%, compared to traditional plans. This showcases its efficacy in optimizing responses to pandemic-induced disruptions within the civil aviation network, offering a comprehensive solution that balances operational efficiency and public health considerations in the face of unprecedented challenges.
... The vehicle scheduling problem concerns the choice of routes for a number of vehicles serving a set of demand points. In 2013, Mou and Zhao (2013) discussed an irregular flight scheduling problem by uncertainty theory. investigated a routing optimization problem in fourth party logistics under emergency conditions, in which the delivery time is regarded as an uncertain variable. ...
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Uncertainty theory, founded in 2007, has become a branch of mathematics to model uncertainty rather than randomness. As an indispensable part of uncertainty theory, uncertain graph and uncertain network optimization has received the wide attention of many scholars. Naturally, a series of original research achievements have been obtained on uncertain graph and uncertain network optimization. This paper aims to present a state-of-the-art review on the recent advance in uncertain graph and uncertain network optimization. Furthermore, it hopes to predict the possible future research directions. Based on Web of Science database, this paper retrieves 144 related papers from 2011 to 2021 to analyze the features of published articles. More precisely, we analyze the annual number of publications, key topics and sub-fields, journals, and most-cited articles. In addition, the main results and models for uncertain graph and uncertain network optimization are summarized. Furthermore, the limitations of existing literature and the possible development trend are discussed.
... However, determining the passenger disappointment spillover cost function remains a problem, and the compensation provided by the airline is a very important 3 factor influencing this cost function. For further research on recovery considering passenger factors, see [16][17][18][19]. Castro et al. [19] give a new approach for disruption management in airline operations control. ...
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The time-band approximation model for flight operations recovery following disruption (Bard, Yu, Arguello, IIE Transactions, 33, 931–947, 2001) is constructed by partitioning the recovery period into time bands and by approximating the delay costs associated with the possible flight connections. However, for disruptions occurring in a hub-and-spoke network, a large number of possible flight connections are constructed throughout the entire flight schedule, so as to obtain the approximate optimal. In this paper, we show the application of the simplex group cycle approach to hub-and-spoke airlines in China, along with the related weighted threshold necessary for controlling the computation time and the flight disruption scope and depth. Subsequently, we present the weighted time-band approximation model for flight operations recovery, which incorporates the simplex group cycle approach. Simple numerical experiments using actual data from Air China show that the weighted time-band approximation model is feasible, and the results of stochastic experiments using actual data from Sichuan Airlines show that the flight disruption and computation time are controlled by the airline operations control center, which aims to achieve a balance between the flight disruption scope and depth, computation time, and recovery value.
... In airline operation area, Rosenberger et al. worked on the simulation software that controls the uncertain delay time [16]. Mou and Zhao built an uncertain programming model with chance constraint and solved it based on classic Hungarian algorithm to deal with the recovery problem under stochastic flight time [17]. Arias et al. proposed a combined methodology using simulation and optimization techniques to cope with the stochastic aircraft recovery problem [18]. ...
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The unexpected aircraft failure is one of the main disruption factors that cause flight irregularity. The aircraft schedule recovery is a challenging problem in both industrial and academic fields, especially when aircraft restoration time is uncertain, which is often ignored in previous research. This paper established a two-stage stochastic recovery model to deal with the problem. The first stage model was a resource assignment model on aircraft schedule recovery, with the objective function of minimizing delay and cancellation cost. The second stage model used simple retiming strategy to adjust the aircraft routings obtained in the first stage, with the objective function of minimizing the expected cost on recourse decision. Based on different scenarios of restoration time, the second stage model can be degenerated as several linear models. A stochastic Greedy Simulated Annealing algorithm was designed to solve the model. The computational results indicate that the proposed stochastic model and algorithm can effectively improve the feasibility of the recovery solutions, and the analysis of value of stochastic solution shows that the stochastic model is worthy of implementation in real life.
... It plays an important role in most manufacturing and service systems [3][4][5]. In traditional scheduling problems, uncertainties will not be considered [1,6]. However, in real cases, disruptions are inherently existent in every manufacturing environment. ...
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A single machine predictive scheduling problem is considered. The primary objective is to minimize the total completion times. The predictability of the schedule is measured by the completion time deviations between the predictive schedule and realized schedule. The surrogate measure of predictability is chosen to evaluate the completion time deviations. Both of the primary objective and predictability are optimized. In order to absorb the effects of disruptions, the predictive schedule is generated by inserting idle times. Right-shift rescheduling method is used as the rescheduling strategy. Three methods are designed to construct predictive schedules. The computational experiments show that these algorithms provide high predictability with minor sacrifices in shop performance.
... A new formulation had been proposed in [3] of this problem based on a cooperative distributed game-theory-based method. For flight scheduling which is a real-time optimization problem, [4] presents a description of the problem in which the total delay minutes of passengers are considered as the optimization objective and which takes into account available resources and the estimated cost of airlines. ...
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