Resource Allocation Model to Find Optimal Allocation of Workforce, Material, and Tools in an Aircraft Line Maintenance

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1 Proceedngs of the Internatonal ultconference of Engneers and Coputer Scentsts 2016 Vol II,, arch 16-18, 2016, Hong Kong Resource Allocaton odel to Fnd Optal Allocaton of Worforce, ateral, and Tools n an Arcraft Lne antenance Rllo S. Wahyudn, Wahyud Sutopo, uh Hsa, R. Suryo Hardono Abstract Ths paper presents a ult-obectve xednteger lnear prograng (ILP) optzaton odel aed at fndng optal resource allocaton based on the study of an arcraft lne antenance. Soe research had already been done to develop such odel, but they anly focus only on fndng the optal allocaton based on an-hour needs wthout consderng the related-cost, such as dfferent hrng cost. Assgnent of the worforce s presuably hghlghted only n respectve sls or tas wth no consderaton of least hrng cost. ost research also consders only one resource n the odel, whch coonly s the worforce. Ths study proposes a resource allocaton odel n an arcraft lne antenance, whch nvolves not only the worforce but also the ateral and tools. In ths paper, we also accoodate the relatonshp between statons n ters of the possblty of resource transfers aongst the. The odel s solved usng the IB ILOG CPLEX software. The result shows that the proposed odel can be used to fnd an optal resource allocaton and the nu total cost. Index Ters Resource Allocaton, ILP, Arcraft Lne antenance, Least Hrng Cost L I. INTROUCTION INE antenance, whch alternatvely called as a short routne antenance, ncludes regular short nspectons of an arcraft between arrval and departure at an arport [1]- [2]. In soe arcraft antenance copanes, lne antenance also ncludes a daly nspecton aed for checng a reanng overnght ar fleet. In an arcraft lne antenance, flght schedule has bascally becoe the bass of the aster plan [2]. Once a flght schedule s establshed, the antenance copany can assgn a antenance schedule to each antenance staton. Based on ths schedule, the copany then bulds a staff schedulng odel, consderng the fleet type, specfc clent requests, etc. [1]- [3]. Furtherore, antenance schedule wll also consder Rllo S. Wahyudn s wth the Industral Engneerng epartent of Sebelas aret Unversty, Suraarta, Indonesa He s an adunct researcher n the RITE group of Sebelas aret Unversty (e-al: [email protected]). Wahyud Sutopo s wth the Industral Engneerng epartent of Sebelas aret Unversty, Suraarta, Indonesa He s a lecturer and dean of the Industral Engneerng epartent of Sebelas aret Unversty. He s also wth the Laboratory of Busness and Logstc Syste n the departent. (e-al: [email protected]). uh Hsa s wth the Industral Engneerng epartent of Sebelas aret Unversty, Suraarta, Indonesa He s a lecturer n the Industral Engneerng epartent of Sebelas aret Unversty. He s also wth the Laboratory of Busness and Logstc Syste n the departent. (e-al: [email protected]). ISSN: (Prnt); ISSN: (Onlne) type of servce, the capabltes of the specfc staton, and other resources such as toolng, hangar, etc. [1]. Resource allocaton has vastly becoe salent n lne antenance. Over 64% of the arcraft antenance copany s expected to set the effcency of resources as ther an goals n the future te [1], [10]. The eployees worng n ths feld are hghly qualfed and specally accredted. Therefore, the supply of new eployees s lted [14]. At the sae te, the wages of such labor are hgh. Consequently, the capactes have to be planned as accurately as possble. Ths coes to no surprse as well snce the cost of lne antenance s ostly attrbuted to labor costs [6], [10]. Worforce plannng s thus crucal n provng syste perforance, effcency and nzng costs. [12]. The resource allocaton supply chan bascally nvolves two an processes: resource procureent and resource transfer. Resource procureent begns wth the resource plannng based on the hstorcal data or deand forecastng n whch flght schedule has generally becoe the bass of the plannng [1], [3]. Flght schedule s n other words the deand/load. After the load s nown, anageent then bulds a staffng odel for that staton, whch specfes the anpower requreent and schedulng to eet the schedule s obectves [1], [9], [12]. In along wth worforce resource, ateral and tools are also becong the allocated resources [2], [16]. The allocaton of these two resources s no dfferent to the worforce where bascally the load fro schedules s specfed accordng to ts fleet type and servce to deterne the ateral and tools needs [9], [16]. The next step s the resource transfer. In ths process, the resource s transferred and assgned to every staton wth regard to ther respectve actual load. What sets the allocaton of worforce and ateral and tools apart s the approach of the allocaton. In allocatng the worforce, tas, sls, and an-hour are what vastly used as the allocaton approach [6], [11], [12]. eanwhle, n allocatng the ateral and tools, the desgnated nuber of allocatons s defned n unt approach [2]. Several research studes have attepted to develop a resource allocaton odel n an arcraft lne antenance. ost research bascally only consders worforce resource n the odel. The allocaton approach s usually wth regard to tas or sls of the respectve worforce [5], [6], [7]. Soe research also consders part or ateral resource nto ther odel, but lewse, t only ncludes the part or ateral resource wthout consderng any other resources,

2 Proceedngs of the Internatonal ultconference of Engneers and Coputer Scentsts 2016 Vol II,, arch 16-18, 2016, Hong Kong le worforce, altogether n the odel [2], [16]. In ths paper, we try to develop a resource allocaton odel n an arcraft lne antenance, whch nvolves not only the worforce but also the ateral and tools. We also accoodate the relatonshp between statons n ters of the possblty of resource transfers aongst the. The odel wll generate an output n the for of nuber of worforce needed based on an-hour approach, not a schedule n a tely anner le ost of exstng research. The allocaton of ateral and tools, n the other hand, wll be n nuber of unts needed. Ths paper s organzed as follows. In Secton I, we descrbe the bacground of our research and descrbe the real proble. In Secton II, we descrbe the ethods. In Secton III, we provde the atheatcal odel forulaton. In secton IV we provde dscusson and In Secton V, we delver the concluson and future research. types are categorzed by the type of arcraft used by the arlne. Load arrves based on a successve span of te or s assued not experencng a clash load n ters of te occurrence. Loads are then reclassfed by types of servce. There are three servces provded n the arcraft lne antenance: before departure chec (B), transt chec (TR), and daly chec (Y). Each servce has ts own respectve standard an-hour and t vares dependng on ts type of load. By ultplyng the total load wth ts respectve standard an-hour per servces, the total an-hour needed wll be obtaned. II. ETHOOLOGY A. Syste escrpton We llustrate our odel usng real lfe syste and data fro a dsgused arcraft antenance copany n Indonesa. The schee of the odel s depcted n fg. 1 below. The resource allocaton s carred out by a plannng dvson n copany s central offce. All statons only act as a feeder assgned to transfer nforaton about ts current load or deand, not as the resource planner. The operatonal staton spreaded out over the land can request addtonal resources or subt ts own resource allocaton schee, but the valdaton s stll beng ade by the plannng dvson n central offce. Plannng vson Request Allocaton Request Bac-up Allocaton Spoes Staton Worforce ateral and Tools Hub Staton Worforce ateral and Tools Load Load Fg. 1. The Resource Allocaton odel used n ths paper Arlnes Arcraft A Arcraft B Arcraft C Arcraft Arcraft E There are two types of operatonal statons,.e. spoes staton and hub staton. Spoes staton s a unt located n spoes arport where bascally the exstng ar traffc wll be bound for the hub arport (traffc feeder). Spoes arports typcally have lower load/deand than hub arports do. Hub staton s a unt located n hub arport whch acts as the hub of several arports that becoe ts spoes. In other words, a hub arport oversees several spoes arports. Besdes beng a traffc center, hub staton also plays to be a bac-up resource of worforce to spoes statons. If a spoes staton experencng a shortage of worforce resources, the staton whch becoes the hub can provde ts avalable or reanng worforce to spoes statons requrng the. The deand/ load s generated fro the arlnes. Load Fg. 2. Least hrng cost schee for worforce assgnent. The gray colun charts ndcate the nuber of worforce that s allocated (Left Axs). The square pont shows the cost of worforce per person (Rght Axs)., whle the dash lne shows the trend. The dar lne shows the trend of allocaton, where the least expensve worforce s allocated ore than the expensve one. Types of worforce are classfed nto 3 categores: peranent worer, techncal support, and outsource worer. In the assgnent procedure, peranent worer poses the hghest prorty of selecton. Ths s because the cost of hrng a peranent worer s the least expensve as copared to the other two. The nuber of peranent worers s lted n accordance wth the nuber of eployees owned by the copany. On the other hand, techncal support s worers assgned fro a hub staton to a spoes staton under ts subordnate. Techncal support s taen fro the peranent worers at the hub staton who s not on the assgnent. The avalablty of techncal support s entrely dependent to the reanng peranent worers poses by the hub staton. Whle outsource worer s a worforce hred fro outsde of the copany or outsourced. Outsource worer s hred on a short ter n order to eet the load requreents that cannot be et by one staton s capacty at the te. The hrng cost of outsource worers s generally the hghest aong others. Ths leads outsource worers to be practcally the least prorty n worforce allocaton. In contrast to the peranent worers, outsource worers do not have lts for specfed aount or are assued always avalable. In aterals and tools allocaton, both resource needs are aggregated nto a sngle one unt. Aggregaton of aterals and tools s further classfed based on the type of load and type of servces. Ths aggregaton s to splfy the deternaton of the allocaton of aterals and tools whch nvolves a lot of types and varants. Every servce for every load ay pose dfferent nd of aggregaton. The provded aggregate of aterals and tools s not lted to a ISSN: (Prnt); ISSN: (Onlne)

3 Proceedngs of the Internatonal ultconference of Engneers and Coputer Scentsts 2016 Vol II,, arch 16-18, 2016, Hong Kong specfed aount or s always avalable. B. Varables and Notaton The varables and paraeters used n ths paper are shown n table I, whle the decson varables are shown n table II. There are seven decson varables n the odel. The decson varable s generally to fnd the optal allocaton of worforce, ateral, and tools n order to satsfy the load. The perforance crtera of the odel s to nze the total allocaton cost.. Sybol I J K l L α f g h f h () TABLE I VARIABLES AN PARAETERS enoted hub staton set spoes staton set load set servce set ateral and tools set odfer coeffcent of nuber of worers nto anhour (nute) hrng costs of peranent worers n spoes staton for hrng costs of techncal support n spoes staton for hrng costs of subcontract worers n spoes staton for hrng costs of peranent worers n hub staton for hrng costs of outsource worers n hub staton for load (dollar) nuber of load n spoes staton for servce l (an) ϖ servce te of load and servce l (nute) S nuber peranent worers avalable n spoes staton (an) S nuber peranent worers avalable n hub staton (an) nuber of load n hub staton for servce l (unt) ( ) O Sybol costs of ateral (dollar) TABLE II ECISION VARIABLES enoted Qt nuber of allocaton of peranent worers n spoes staton for load (an) b nuber of allocaton of techncal support n spoes staton for load (an) q nuber of allocaton of outsource worers n spoes staton for load (an) Q nuber of allocaton of peranent worers n hub staton for load (an) q nuber of allocaton of outsource worers n hub staton for load (an) () nuber of allocaton of ateral and tools n spoes staton for load, and servce l (unt) () nuber of allocaton of ateral and tools n hub staton for load, and servce l (unt) III. OEL FORULATION The resource allocaton s carred out by the plannng dvson n collaboraton wth both spoes and hub statons whch provde the nforaton about recent and actual load of ther respectve statons. In order to obtan the optal cost and resource allocaton, resource selecton n ters of least hrng cost, an-hour needs and avalablty, nuber of unts of ateral and tool needs are taen nto the rules of allocaton. The obectve s nvolvng two staeholders: the spoes staton and the hub staton. A. The Resource Allocaton The ncong load wll generate the resource needs of worforce, ateral and tools. When loads coe to a staton, each of the ust be fulflled entrely. There should not be any unfulflled or unsatsfed load. Every load ust be et whether usng the resource fro nsde of the staton or outsde of the staton. The fulfllent of one load wll consue a certan aount of an-hour and a unt of ateral and tools aggregate. an-hour consuptons as well as the ateral and tools aggregate vary accordng to load type and the servce t taes. The worforce needs depends on the nuber of an-hour needed to fulfl all loads. Peranent and outsource worers provde a total of 6 effectve worng-hour a day. Whle techncal support provde 4.5 effectve worng-hour a day. The avalable worng hour n-staton s generated only fro the total worng hour of the peranent worers. If the avalable worng hour n-staton s not suffcent to fulfll the an-hour needed to satsfy all loads, the addtonal outstaton an-hour should be provded to overcoe the defct. It ay coe whether fro the techncal support or the outsource worer. For hubs staton, only outsource worer feasble to be allocated apart fro the peranent worers. The relatonshp between the allocated an-hour and the nubers of an-hour needed to fulfl the load s forulated n Eq. (1) and Eq (2) below. Both Eq. (1) and Eq. (2) expresses that the total an-hour to be allocated ust be equal or greater than the total an-hour needed to fulfl the load. Eq. (1) represents the spoes staton whle Eq. (2) represents the hub statons. Eq. (3) and Eq (4) forulates the relatonshp between nubers of ateral and tools to be allocated and nubers of unt needed. Both equatons expresses that the allocaton of ateral and tools should be equal or greater than the nubers of unt needed. Eq. (3) represents the spoes staton whle Eq. (4) represents the hub statons. Unle the worforce, the avalablty of ateral and tools resource s assued to be always avalable. Q ) ll I Q I ll b q ( (1) ) ll I ll I q ( (2) B. Spoes Staton Obectves ll J ll Spoes staton s obectve s to nze the total allocaton cost. The cost of allocaton s obtaned by enueratng all resource allocaton cost, ang up the total (3) (4) ISSN: (Prnt); ISSN: (Onlne)

4 Proceedngs of the Internatonal ultconference of Engneers and Coputer Scentsts 2016 Vol II,, arch 16-18, 2016, Hong Kong cost. In spoes staton, there are four nds of resources nvolved: peranent worer, techncal support, outsource worer, and ateral and tools. The spoes staton s obectves can be forulated as n Eq. (5). The frst three ters represent the cost of the worforce, whch conssts of peranent worers cost, techncal support cost, and outsource worers cost. Though the source s taen fro the hubs, the cost of techncal support s charged to the benefcares, whch n ths case s the spoes staton. The last reanng ter of the equaton represents the total allocaton cost of ateral and tools. Q f b g q h ll C. Hub Staton Obectves o (5) The hub staton s obectve s to nze total allocaton cost whch n other words optzng the resource allocaton. Unle spoes staton, the hub staton coprses only three nds of resources: peranent worer, outsource worer, and ateral and tools. The techncal support s not taen nto the hub staton obectve consderaton snce t s bascally only feasble to spoes staton. Though the source of techncal supports s orgnated fro the hub staton, the expenses of the worforce are charged to the spoes staton, whch benefts the resource, not the orgnal hub statons assgned the worforce. Hence the hub staton obectve can be forulated as n Eq (6). I Q f I ll I o q h The frst ter of Eq. (6) s the frst obectve of hub staton, whch s to nze the peranent worer cost. The second ter presents the second obectve of hub staton, whch s to nze the outsource worer cost. Whle the last ter defnes the thrd obectve whch s to nze the ateral and tools cost. The ult obectves of Eq. (7) are to nze both allocaton of spoes staton and hub staton. It coprses of two ters, Z1 represents the total allocaton cost of spoes arport and Z2 represents the total allocaton cost of hub staton. Z1 Z2 (6) ax. Z1+ Z2 (7) Q f b g q h ll I o (8) Q f I ll I o q h (9) Subect to: Q b ) ll Q S I Q I ll q ( (10) ) ll I ll I Q I q (11) ( (12) b ll J ll S (13) (14) (15) Q t, b, q, Qt, q,, (16) The avalable peranent worers n spoes statons s expressed n Eq. (11). Ths expresson s to ensure that the allocaton of peranent worers does not exceed the supply the staton house. Slar to Eq. (11), Eq. (15) also expresses the avalable peranent worers, but for hubs statons. Snce hub statons are able to send soe of ther peranent worers to the spoes staton as a techncal support, the avalable peranent worers wll be deducted by the nuber of techncal support assgned to spoes statons. The last equaton s utlzed to force non-negatvty for all decson varables (Eq. 16). IV. ISCUSSION For coputatonal study, IB ILOG CPLEX Acadec verson s used as a tool for solvng the odel. ILOG CPLEX s bascally slar to soe other coon prograng softwares, however ILOG CPLEX s partcularly desgned to be capable of solvng, ostly, about optzaton and varous equatons or odelng. In ths study, there are a total of 4 hub statons and 8 spoes statons wth = Hub 1, Hub 2, Hub 3, Hub 4; and = Spo 1, Spo 2, Spo 3, Spo 4, Spo 5, Spo 6, Spo 7, Spo 8. Hub 1 subordnates Spo 1 and Spo 2 whle Hub 2 subordnates Spo 3, Spo 4, and Spo 5. Hub 3 subordnates Spo 6 and Spo 7, and Hub 4 subordnates Spo 8. Cost ($/unt) TABLE III COST OF ATERIAL ateral Type ateral and tools coprse 15 types of aggregate wth = at 1, at 2, at 3, at 4, at 5, at 6, at 7, at ISSN: (Prnt); ISSN: (Onlne)

5 Proceedngs of the Internatonal ultconference of Engneers and Coputer Scentsts 2016 Vol II,, arch 16-18, 2016, Hong Kong 8, at 9, at 10, at 11, at 12, at 13, at 14 and at 15. Each ateral and tools aggregate has ts own respectve cost shown n table III whle cost of worforce s shown n table IV. The peranent worer s hrng cost s the least expensve aong the others. Techncal supports hrng cost stands next to peranent worers as the second least expensve cost. Hub statons do not have a techncal support allocaton snce t s not elgble for the to have one. Whle outsource worers coe at last havng the hghest hrng cost. Staton TABLE IV COST OF WORKFORCE Peranent Worer ($/hour) Techncal Support ($/hour) Outsource Worer ($/hour) Hub N/A 25.5 Spo Spo Hub N/A 25.5 Spo Spo Spo Hub N/A 25.5 Spo Spo Hub N/A 25.5 Spo On the other hand, there are 5 types of load wth = A, B, C,, E whle servce coprses three types of servce wth l = Y, TR, B. Not all statons have every type of load and servce. Soe statons ay only have two or three loads and several servce types. Load data are shown n table V below. Load A B C E Servce Hub 1 Spo 1 Spo 2 TABLE V LOA ATA Hub 2 Spo 3 Staton Spo 4 Spo 5 Hub 3 Spo 6 Spo 7 Hub 4 Spo 8 TR B Y TR B Y TR B Y TR B Y TR B Y The results of the odel s depcted n a graph n Fg. 3 and n a table n table VI. It s found that all allocated worforce has satsfed the total an-hour needed and all allocated ateral and tools has satsfed the total unt needed to serve the load. Based on the result, the average slac or reanng unused an-hour of the allocated worforce s n ts ost possble closest nuber to the an-hour needed, whch s no greater than 8%. Whle the slac of ateral and tools reans 0. Fro the followng Fg. 3, t can be nferred that soe statons are stll able to eet the an-hour needs fro the n-staton worforce resource whle soe s not. Fg. 3. Allocaton of worforce. Blac coluns ndcate outsource worer allocaton. Whle grayscale colun and dash-flled coluns ndcate peranent worer and techncal support allocaton respectvely. ateral Type TABLE VI ALLOCATION OF ATERIAL AN TOOLS Spo 1 Spo 2 Spo 3 Spo 4 Spo 5 Spo 6 Spo 7 Spo 8 Hub 1 Hub 2 Hub 3 Hub 4 at at at at at at at at at at at at at at at The allocaton of the worforce n statons experencng a an-hour shortage s partally covered by the outsource worforce, and soe other staton s coverng the shortage through worforce transfer of techncal support fro the hub. Ths occurs especally n Spo 5 n whch ts hub, the Hub 1, stll has a reanng unassgned worforce. The allocaton of ateral and tools s generally ade up by at 1 about 47%, followed by at 10 and at 4 wth percentage of 19% and 13% respectvely. The nu total allocaton cost of worforce, ateral, and tools s obtaned at US 31,880. V. CONCLUSION In ths paper, we propose a resource allocaton odel for an arcraft lne antenance consderng the resource of worforce, ateral, and tools. ult-obectve optzaton prograng was eployed to deterne the optal resource allocaton of the worforce together wth the ISSN: (Prnt); ISSN: (Onlne)

6 Proceedngs of the Internatonal ultconference of Engneers and Coputer Scentsts 2016 Vol II,, arch 16-18, 2016, Hong Kong allocaton of ateral and tools. The result shows that the odel s capable to fnd the optal soluton n along wth the nu allocaton cost. The resource allocaton odel deternes not only the allocaton of the worforce, but also the allocaton of ateral and tools. The relatonshp of a spoes and a hub staton n ters of resource transfer can also be explaned whch n so any odels the relatonshp has never been taen nto consderaton. There are soe extensons of ths study that could be derved to elaborate the forulaton of ths proposed atheatcal odel, such as the possblty n whch the ncong loads arrves concurrently. Ths wll lead to soe odfcaton of constrant n the odel because t s not possble for the worforce to serve several loads at the sae te. In the future, the addton of several ore types of worer n ters of sl capablty, apart fro the occurrence of dfferent hrng cost, ay also be taen nto consderaton to ae the odel ore versatle. VI. ACKNOWLEGENT The tea would le to than the Research Group of Industral Engneerng and Techno-econocs (RITE) of Sebelas aret Unversty for the fnancal support of ths research. REFERENCES [1] P. Gupta,. Bazargan and R. N. cgrath. Sulaton odel for Arcraft Lne antenance Plannng. In Proc. Annual Relablty and antanablty Syposu. IEEE, [2] J. V.. Bergh, P.. Bruecer, J. Belen, L.. Boec and E. eeuleeester. A Three-stage Approach for Arcraft Lne antenance Personnel Rosterng Usng IP, screte Event Sulaton and EA, Elsver. Expert Systes wth Applcatons, vol. 40, pp , [3] Yan, S., Yang, T., and Chen, H. Arlne short-ter antenance anpower supply plannng, Transportaton Research Part A: Polcy and Practce, vol. 38, [4] L. En-nahl, H. Allaou and I. Nouaour. 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