Airport risk assessment: a probabilistic approach

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1 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 Arport rsk assssmnt: a probablstc approach L. GUERRA, T. MURINO, E. ROMANO Dpartmnt of Matrals Engnrng and Opratons Managmnt Unvrsty of Napls Fdrco II p.l Tccho 805 Napol ITALY Abstract: Rsk rducton s on of th ky objctvs pursud by transport safty polcs. Partcularly, th formulaton and mplmntaton of transport safty polcs nds th systmatc assssmnt of th rsks, th spcfcaton of rsdual rsk targts and th montorng of progrsss towards thos ons. Rsk and safty hav always bn consdrd crtcal n cvl avaton. Th purpos of ths papr s to dscrb and analys safty aspcts n cvl arports. An ncras n arport capacty usually nvolvs changs to runways layout, rout structurs and traffc dstrbuton, whch n turn ffct th rsk lvl around th arport. For ths rasons thrd party rsk bcoms an mportant ssu n arports dvlopmnt. To avod subjctv ntrprtatons and to ncras modl accuracy, rsk nformaton ar colltd and valuatd n a ratonal and mathmatcal mannr. Th mthod may b usd to draw rsk contour maps so to provd a gud to local and natonal authorts, to populaton who lv around th arport, and to arports oprators. Ky-Words: Rsk Managmnt, Rsk assssmnt mthodology, Safty Cvl avaton. Introducton Rsk rducton s on of th ky objctvs pursud by transport safty polcs. Partcularly, th formulaton and mplmntaton of transport safty polcs nd th systmatc assssmnt of th rsks, th spcfcaton of rsdual rsk targts and th montorng of progrsss towards thos ons. Furthrmor, targtng phas nds a dp analyss to balanc fforts, achvablty, publc and poltcal accptablty of th polcs to b mplmntd [4]. Rsk assssmnt rangs from th ntrprtaton of th avalabl data concrnng frqunt thrats or th stmaton of vry rar vnts lklhood: combnng ths nformaton wth th xpctd loss would rsult n quantfyng th rsk xposur ndx. Rsk assssmnt s an ssntal procss n makng polcy dcsons for rsk managmnt. By dntfyng th natur and scal of th potntal mpact on consumrs or mploys, rsk assssmnt can assst rgulatory authorts and busnss organzatons to dtrmn what typ of acton s ndd [3]. Rsk and safty hav always bn consdrd crtcal n cvl avaton [6]. An arport s a multfuncton dstrbutd systm that s part of a much largr systm. You can thnk of t as bng at th cntr of a dynamc ntwork mad up of all th sourcs of cargo, passngrs and th othr popl who travl to and from th arport; vstors, clanrs, t ala. But that s just th ground systm; a larg numbr of ths ntworks ar ntrconnctd to form a hug communcatons ntwork; th nods ar th arports wth thr hntrlands, and th dalogus ar mad up of arcraft [3]. Arports prsnc causs a convrgnc of ar traffc ovr th surroundng ara so, popl who lvs n that ara ar unconscously xposd to arcraft accdnts rsk. Actually, local rsk lvls ar hghr than mght b xpctd. In fact, vn f t s tru that th accdnt pr flght ndx s vry low (typcally pr 0 6 ), statstcs dmonstrat that accdnts mostly happn durng tak-off and landng phass and hnc, clos to th arport. Morovr, th low probablty of an accdnt pr movmnt f combnd wth th hgh numbr of flght opratons (typcally svral hundrds of thousands) may suggst th probablty of on accdnt to b hghr than w could xpct. Rsk lvl around larg arports ar, n ffct, of th sam ordr as thos assocatd wth partcpaton n road traffc. An ncras n arport capacty usually nvolvs changs to runways layout, rout structurs and traffc dstrbuton, whch n turn ffct th rsk lvl around th arport. For ths rasons thrd party rsk bcoms an mportant ssu n arports dvlopmnt. In th lat 990s th world s arln flt conssts of mor than arcraft flyng a ntwork of approxmatly 5 mllon km and srvng narly arports. Th sctor drctly mploys mor than 3.3 mllon popl, wth ovr.4 mllon n USA [5]. Som bllon popl and 3 mllon tonns of frght ar bng movd annually. Th frght fgur rprsnts approxmatly on thrd of valu of th world s manufacturd xports. A varty of ntrnatonal nsttutons, organsatons and agncs dal wth forcastng futur trnds, ncludng Intrnatonal Cvl Avaton Organzaton (ICAO) and Intrnatonal Ar Transport Assocaton (IATA). Th arspac manufacturrs such as Arbus Industry, Bong and Rolls Royc also mak ISBN: ISSN:

2 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 projctons. Hstorcally, whn thr has bn rlatvly rapd growth n ar transport, t has oftn bn followd by a srs of accdnts. Th occurrnc of such vnts has stmulatd th ntroducton of tchncal and opratonal masurs. As a rsult, ovrall safty has mprovd ovr tm. So, thr s a currnt mov to wdn th adopton of Safty Managmnt Systms (SMS) wthn th ar transport ndustry whch carrs wth t a nd to undrtak rsk assssmnts, thr qualtatv or quanttatv. As an xampl n th UK, th CAA dscrbs th mans of mplmntaton of SMS by an arcraft oprator [7]. Rsk assssmnt s an ssntal part of such a systm, and CAP7 thrfor ncluds a rsk tolrablty matrx for us whn quantfyng rsk. Th dscpln of rsk assssmnt has bn appld n th arcraft systms, as rqurd for arcraft crtfcaton undr FAR3, FAR5 n U.S.A and undr EASA Crtfcaton Spcfcaton (CS)-3/5 n Europ. Tchnqus for accomplshng th assssmnt of safty ar quotd by th SAE n thr Arospac Rcommndd actc (ARP) Flght Opratons Rsk Assssmnt Systm, known as FORAS [4], s a rsk managmnt tool to ncod human knowldg about a typ of rsk. Th FORAS mthodology mploys a fuzzy xprt systm to dntfy th factors whch hav th gratst mpact on ovrall rsk. A dffrnt approach has bn adoptd by [9] who has dvlopd th Avaton Safty Rsk Modl (ASRM). Ths maks us of th Human Factors Analyss & Classfcaton Systm (HFACS) proposd by [7]. HFACS s a classfcaton schm whch has bn dvlopd to captur and analyz th dffrnt typs of human rror that may occur. Th framwork draws on [], n whch was dvlopd th so-calld Swss-chs modl of accdnt causaton. ASRM was orgnally dvlopd for us by US Naval Avaton, but has snc bn usd mor wdly wthn th avaton ndustry. Th ASRM uss Baysan Blf Ntworks to modl th uncrtanty wthn th modl, usng thr data or th opnon of xprts. An addtonal tchnqu has bn adoptd by Bazargan and Ross [6], who usd th proportonat occurrnc of causal factors obtand from accdnt rports, whr fatalts or srous njurs wr rportd. Ths nformaton s thn combnd wth xprt judgmnts on th rlatv mportanc of th flght attrbuts usng Analytcal Hrarchy ocss (AHP). Th purpos of ths papr s to dscrb and analyz th problm of safty aspcts n arports payng attnton to th followng aspcts: a stratgc approach to mprov arport safty, whch ncluds th us of falur and hazard analyss tchnqus and fast tm smulaton modllng; safty of land sd opratons; crtfcaton aspcts. To avod subjctv ntrprtatons and to ncras modl accuracy, rsk nformaton ar colltd and valuatd n a ratonal and mathmatcal mannr. Th mthod may b usd to draw rsk contour maps so to provd a gud to local and natonal authorts, to populaton who lv around th arport, and to arports oprators. Dfntons A rsk s th combnaton of th probablty, or frquncy, of occurrnc of a dfnd hazard and th magntud of th consquncs of th occurrnc [7]. Th combnaton of ths paramtrs dtrmnats a two dmnsonal quantty. So, f th rsk s to b rducd, t can b thr b don n th svrty axs, or n th lklhood axs, or both. To ffct a dcras on both axs may b consdrd th bst approach to rsk rducton. For natural hazards such as an arthquak, typcally w cannot do anythng to rduc th lklhood, but thr s much that can b don to rduc th consquncs: spcal buldng rgulatons can b put n plac and arthquak kts can b pr-dstrbutd to nhabtants. Altrnatvly, thr s much that can b don to rduc th chancs of happnng of a md ar collson of two arcraft: th ar traffc control systm and on.-board radars ar n plac to montor and mantan both vrtcal and horzontal sparaton. Gnrally spakng, rsk assssmnt procdur ams [3]: to drv th lklhood and th svrty of consqunc valus for ach hazard; to us obtand nformaton as a mans of prortzng actons; to spcfy mtgatng faturs as approprat to ach hazard; to prdct th ffctvnss of thos faturs n rducng th rsk. A frst, ntutv dfnton of th trm rsk, coms from th fact that thr s rsk f thr xsts a potntal sourc of damag, or hazard. Whn an hazard xsts (.g. a systm whch n crtan condtons may caus undsrd consquncs), safguards ar typcally dvsd to prvnt th occurrnc of such hazardous condtons and ts assocatd undsrd consquncs. Howvr, th prsnc of an hazard dos not suffc tslf to dfn a condton of rsk. Indd, thr s th uncrtanty that th hazard translats from potntal to actual damag. Thus, th noton of rsk nvolvs som knd of loss or damag that mght b rcvd and th uncrtanty of ts transformaton n an actual loss or damag so, rsk = damag uncrtanty. Ths qualtatv analyss s rflctd n th varous Dctonary-dfntons of rsk, such as possblty of loss or njury and th dgr of probablty of such loss. Lt x and p rspctvly rfr as a gvn damag and th probablty of rcvng such damag. From a quanttatv pont of vw, a masur of th assocatd rsk R s: R = x p () ISBN: ISSN:

3 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 In practc, th prcpton of rsk s such that th rlvanc gvn to th damagng consquncs x s far gratr than that gvn to ts probablty of occurrnc p so that q. () s slghtly modfd to: R k = p x, k > () By so dong, numrcally largr valus of rsk ar assocatd to largr consquncs. Whn consdrng complx systms, th abov quanttatv dfntons must b xtndd to account for th fact that typcally mor than on undsrabl vnts xst. Wth n undsrabl vnts assocatd wth th opraton of a gvn systm (compost rsk), quaton () changs n: n R = x t pt (3) t= and smlarly t s don for q. (). Ths quanttatv dfntons of rsk ar asly shown to b lttl nformatv for th purposs of rsk analyss, managmnt and rgulaton. Suppos you wr consdrng two dffrnt systms A and B of qual rsk R A = R B as dfnd (). Lt th rsk of A b du to a potntally larg consqunc x A occurrng wth small probablty p A and vc vrsa for th rsk of B. Thn, f w wsh to act on th dsgn, opraton and rgulaton of th two systms n ordr to rduc th assocatd rsks, w wll act dffrntly knowng th dffrnt naturs of th rsk n th two cass. To rduc R A w would mplmnt mtgaton and protcton, on th contrary, f w wr to rduc R B w would do som prvnton. Thus, f w smply know th valu of R, w may not b ffctv n rducng t by lmtng ts probablty part or by mtgatng ts consquncs; hnc, th mportanc of kpng sparat th consttunts of rsk, p and x. Th stuaton s, naturally, wors n th cas of th compost rsk. Not also that, gnrally spakng, a good approach to rsk rducton s: prvnton, mtgaton, protcton, rsdual rsk managmnt. So, an nformatv and opratv dfnton of rsk should allow answrng th followng qustons: Whch squncs of undsrabl vnts transform th hazard nto an actual damag? What s th probablty of ach of ths squncs? What ar th consquncs of ach of ths squncs? Th rsk s, thn, dfnd n trms of a st of trplts: {( s, p x )} R =, t t t whr s s th squnc of undsrabl vnts ladng to damag, p s th assocatd probablty and x th consqunc. In rlatonshp to th typ of vnts, t s possbl to dfn thr typologs of rsk: Convntonal rsks: thy ar rlatv to vry frqunt vnts and thy ntrst on or two popl; Spcfc rsks: thy ar rlatv to contnuous or frqunt vnts wth modst damags n brf tms; Grat potntal rsks: thy ar connctd to vry rar vnts wth srous damags. Ths last rsks ar th objct of th proposd modl and w wll rfr to thm smply as rsk of accdnt. In th cas n whch th rsk of accdnt would b ntolrabl, som actons wll b found to attnuat ts ntnsty accordngly to th mntond approach. In ths papr, vnts ar classfd accordng to th followng dfntons furnshd by th Natonal Transportaton Safty Board (NTSB) and th Intrnatonal Cvl Avaton Organzaton (ICAO): Arplan accdnt: An occurrnc assocatd wth th opraton of an arplan that taks plac btwn th tm any prson boards th arplan and th tm all such prsons hav dsmbarkd; Hull loss (Srous Incdnt): Arplan damag that s substantal and s byond conomc rpar; Substantal damag (Incdnt): Damag or structural falur that advrsly affcts th structural strngth, prformanc or flght charactrstcs of th arplan and would normally rqur major rpar or rplacmnt of th affctd componnt; Fatal accdnt: An accdnt that rsults n fatal njury; Fatal njury: An njury that rsults n dath wthn 30 days as a rsult of an accdnt; Srous njury: An njury sustand n an accdnt that: Rqurs hosptalzaton for mor than 48 hours that bgns wthn 7 days of th dat of njury; Rsults n a fractur of any bon (xcpt smpl fracturs of fngrs, tos, or nos); oducs lacratons that rsult n svr hmorrhags or nrv, muscl, or tndon damag; Involvs njury to any ntrnal organ; Involvs scond or thrd dgr burns ovr 5% or mor of th body; Involvs vrfd xposur to nfctous substanc or njurous radaton. To stand any chanc of achvng ths goals w frst nd an hazard dntfcaton. Whn buldng a larg systm from a numbr of smallr ons w fnd that many of th hazards ars from th ntra-systm ntrfacs [3]. Whn prformng a rsk assssmnt, thn, w can start off by dntfyng thos ntrfacs and th hazards arsng from thm. Whr a systm s mad up of subsystms from dffrnt supplrs thr domans of nflunc also nd to b consdrd. An arport has a lot of ntrfacs wth outsd world: ar traffc control has rado and tlphons, thr ar navgatonal ads that communcat wth arcraft (nstrumntal landng systms), thr ar road/ral lnks, tc. W wll consdr only on arsd ntrfac, th runway: whch s th ntrfac btwn th ar navgaton systm and ISBN: ISSN:

4 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 th ground handlng ara. 3 Safty Data Rcords Th arport rsk assssmnt ncluds a srs of connctd actvty: vnts hstorcal analyss; accdnt frquncs dtrmnaton; magntud and th rsk valuaton. Informaton wr acqurd by: nvstgatng arcraft accdnts causs; accdnt locaton; accdnt consquncs. Accdnt data ar obtand, whn avalabl, from govrnmnt accdnt rports. Othrws, nformaton s solctd from oprators, manufacturrs, varous govrnmnt and prvat nformaton srvcs. Such nformaton s nfrrd by a hstorcal analyss of th vnts, makng rfrnc to:. local fls (ANSV);. world fls (AAIB, AAIU; ATSB; NTSB; TSB, tc.). In ordr to dtrmn a tool that allows a brf and xhaustv dscrpton of th analyzd arcraft accdnts, as wll as a support to rcord th frst nws of an nvstgaton, a rport has bn compld (Fg. ). Fg. - A synthtc schm to collct a prncpal factors concrnng arcraft accdnt In ths rport th ID_NUMBER s th cod of th analyzd rport whras th fld DATE AND HOUR ndcats th dat and th tm whn th accdnt has happnd (n conformty wth th prscrptons of th ICAO Annx 3, t s xprss n local or coordnatd unvrsal schdul UTC, Unvrsal Tm Coordnatd). LOCATION s th plac n whch th accdnt s occurrd and AIRCRAFT_ID s th typology of arcraft ntrstd by th accdnt (n our cas commrcal arplans). Th fld CLASS ndcats th class of th arcraft dfnd n rlatonshp to ts maxmum takoff wght (MTOW), dntfd wth th followng lttrs: A: arcrafts wth MTOW < Kg wth an only motor; B: arcrafts wth MTOW < Kg and two motors; C: arcrafts wth kg < MTOW < kg; D: arcrafts wth MTOW > Kg and mor than two motors. FLIGHT_CONDITIONS ar th flght mtorologcal condtons bfor and durng th accdnt vnt dstngushd n: VFR (Vsual Flght Ruls): t dals wth a flght prformd wth th vsual rfrncs ad. Naturally th possblty to ffct vsual flghts s td up to th xstnc of an nough vsblty (VMC, Vsual Mtorologcal Condton). In th chckd aral spacs th last VMC ar: flght vsblty n 8 Km, dstanc from th clouds,5 Km n horzontal drcton and 300 m n vrtcal drcton. In Italy th vsual flght ruls ar forbddn n th nght tm hours and th flght hav to sustan undr th 600 ms of hght, cannot b landd n VFR wth vsblty to th ground lssr than 8 Km and wth clng lssr than 450m; IFR (Instrumnt Flght Ruls): whn th flght s prformd usng radofrquncy ads (VOR, NDB, DME, TACAN, tc.). In th fld MANOUVRE_CONDITIONS th manuvrs that th arcraft was prformng durng th accdnt ar rportd (landng and takoff n IFR or VFR condtons, tc.). Th EVENT_TYPE s th typology of arcraft accdnt: run off: t s frqunt n th cas of long landng or abortd tak-off; vr off: t s rlatv to an arcraft sd off and can happn both n tak-off phas and landng; t can b du to an lvatd valu of th wnd transvrs componnt, to a mchancal brakdown, tc; short landng: t s rlatv to a touchdown happnd bfor th runway thrshold. It s du, manly, to bad mtorologcal condtons; run ncurson: t occurs both n tak-off phas and landng and can concrn both arcrafts and othr vhcls. In th fld FLIGHT PLAN thr s a synthtc dscrpton of th flght plan prformd by th plan. Partcularly t rcords th dpartur arport and hs d cod, ntrmdary arports, th dstnaton arport and th flght typology. METEOROLOGICAL_CONDITIONS ar th condtons rcordd n th plac of th accdnt durng th vnt. Partcularly, thy rgards th prsnc and hght of th clouds, vsblty, wnd drcton and ntnsty, prcptaton, tmpratur and dwy pont. In th fld SYNTETIC EVENT DESCRIPTION thr s a brf but xhaustv dscrpton of th accdnt dynamcs. In such dscrpton ar undrlnd: n landng phas, th touchdown pont n whch th accdnt s vrfd and th stop pont n whch th ISBN: ISSN:

5 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 arcraft or vntually dbrs ar rnvntd; n tak-off phas, th pont n whch th accdnt s vrfd and th stop pont n whch th arcraft or vntually dbrs ar rnvntd. In ths rport th PROBABLE CAUSES ar that brought to th accdnt ar rportd too. Essntally w rfr to human factors, mchancal factors or nvronmntal factors. Evn f ths factors ar not ntrdpndnt, thy can ntract. Mchancal and nvronmntal factors ar obvously unchangabl n th brf prod: thr s only th possblty to act on human rrors applyng prvntv masurs that am to rduc th accdnt. As concrn human rrors typology, th followng classfcatons can b mad: actv falurs (rrors or actv drawbacks): rrors or drawbacks that hav an mmdat ngatv ffct; latnt falurs: falurs xstng bfor th vnt. A dscrpton of th faturs ntrstd by th accdnt s rportd n th fld AIRPORT FEATURES INTERESTED: RWY, TWY, Apron or also th zon whr th accdnt s occurrd, as wll as th stat n whch was found durng th accdnt. Som ntrstng arport faturs about runways ar: a synthtc dscrpton of th gomtrc charactrstcs: lngth, wdth, longtudnal and transvrsal nclnaton, prsnc of stop way and hs dmnsons, TORA (Tak Off Run Avalabl), TODA (Tak Off Dstanc Avalabl), ASDA (Acclrat and Stop Dstanc Avalabl), LDA (Landng Dstanc Avalabl), runway nstrumntatons, ILS systm for landng. Partcularly, n rlatonshp to th runway vsual rang and to th dcson hght, th ILS s dvdd n ILS of CAT I, t allows an approach of prcson untl to a hght of dcson of 60 mt and a RVR of th 800m, ILS of CAT II, t actually allows an approach of prcson to a dcson hght of 30 mt and a RVR of th of 400 ms, ILS of CAT III, t allows an approach of prcson wthout som dcson hght and a RVR btwn th 00 and 50 mt; th pavmnt condtons durng th accdnt. To dfn aforsad condtons s mad rfrnc to th ICAO trmnology. Th followngs trms w hav bn usd: damp, to pont out that th surfac shows changs of color bcaus of th damp; wt, to pont out that th surfac s full watr, but thr s no puddls; watr patchs, to pont out that on th surfac thy ar vsbl puddls; floodd, to pont out that on th surfac thy ar vsbl ampl zons covrd of watr. If thr s som c on th runway th trms usd ar: rm or frost covrd normally to th mllmtr, dry snow, wt snow, slush, c, compactd or ruld snow, frozn ruts or rdgs. Th EVENT_SCHETCH s a graphc accdnt rprsntaton n whch th ponts n th synthtc dscrpton of th accdnt and a possbl photographc documntaton ar undrlnd. 3. Exprmntal analyss: acquston and laboraton data For ach accdntal vnt, rlvd trough th govrnmnt or othrs oprators accdnt rports, proposd rport has bn compld. Acqurd data allowd to stablsh that th 46,4% of th.74 commrcal arplans accdnts concrnd th arport (58,5% concrnng th RWY, 33,6% concrnng th apron and 7,9% concrnng th TWY) and th 8,% th approach paths. As concrn rsk vnts typology: 40,% ar accdnt, 54,7% ar ncdnt and 5,% ar srous ncdnt. From ths rsults mrgs that durng th taxng manuvrs, from and for th runway, and thos of standstll n th trmnal ara, thr arn t human damags f w xcpt far or lght njurs. On th othr hand, th accdnts durng th tak-off or landng phass ar charactrzd by an hgh prcntag of njurs and daths. Indd, n ths papr apron manuvrs hav not bn consdrd. Invstgatng causs of thos fatal arcraft accdnts s dffcult bcaus thy gnrally stm from a complx systm of mutually dpndnt, squntal factors. Ths factors can b classfd n svral ways. At frst, accordng to th currnt stat-of-knowldg, thy can b catgorzd nto known and avodabl and unknown and unavodabl causs. Th formr should b consdrd condtonally n th sns that mmdatly aftr an accdnt th ral causs ar sldom fully known but as th nvstgaton progrsss thy bcom known and avodabl. Thn, wth rspct to accdnt typ, th man causs can condtonally b classfd nto human rrors, mchancal falurs, hazardous wathr, sabotags or mltary opratons. As concrn data about th accdnts happnd on th runway, a 75% of ths ons happn n th landng phas and th rmanng 5% n th tak-off manuvr. Consdrng th sngl manuvrs: n th landng phas, th 66% of th accdnts ar du to human rrors, 0% to mchancal falurs and 4% to mtorologcal condtons; n th tak-off phas, th 45,5% of th accdnts ar du to human rror, 45,5% to mchancal falurs and 9% to mtorologcal condtons. Thrfor, whl n landng phas th prdomnant caus s rprsntd by th human rror, n th tak-off thr s no dffrnc btwn mchancal falurs and human rrors. 4 A rsk assssmnt mthodology Basc lmnt to conduct a statstcal analyss of an vnt s th sampl data dscrpton and dtrmnaton. In ths study ISBN: ISSN:

6 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 th sampl lmnts ar th commrcal arcrafts nvolvd n runway accdnts n tak-off and n landng phass. Spcfcally w hav not consdrd: th mssd collsons n th runway among two arcrafts or among ths and an any othr vhcl; th damags of th arcrafts n tak-off phas that has not brought any harmful ffct; th arcrafts that, durng th landng phas has suffrd falurs and wnt out th runway wthout furthr problms. Th our modl calculatng arport rsk accdnts s composd by thr man lmnts: th probablty modl of an occurrnc of arcraft accdnt and th accdnt locaton probablty modl to dtrmn th frquncy of an occurrnc p n (); th accdnt consqunc modl n ordr to dtrmn th x varabl n (). 4. Th arcraft accdnt probablty modl Of ths study phas has bn th subdvson of th surroundng ara runway n sofrquncy lns or rathr zons charactrzd by th sam commrcal arcraft accdnt probablty (as shown n fgur ). Th modl as a rsult was born from a carful analyss of th ncdntal phnomnon, partcularly of th varous phass that hav brought to th arcraft arrst outsd runway, both n tak-off and n landng phass. It has mrgd that th ntrstd vnts (th touchdown pont or tak-off ntrrupton phas; th accdnt causs; th arcraft or dbrs stop pont) may b consdrd. Such vnt can occur randomly any tm and n any pont n spac. Past arcraft accdnts had ths faturs. Thy occurrd n a random mannr n dffrnt parts of th world. Thrfor t s possbl to dtrmn th frquncy of an occurrnc through a partal shars modl. Partcularly fxng a Cartsan rfrnc (x, y) wth axs x concdnt wth th runway, and w hav subdvdd th ara of study through squard or rctangular grd. It wll b possbl to calculat th p probablty that th arplan or dbrs, nvolvd n a gnrc accdnt, blongng to class, stops n a dtrmnd pont (B) cntr of th gnrc unt grd. Ths probablty s rlatd to th probablty that dfn touchdown or abortd tak-off pont (A). Thn w hav th followng rlatonshp: n I { B} = {} I { A} { B / A} (4) n whr: n s th prcntag of arplans rlatd to wght n class that landng or tak off from th arport objct of ths study; n {} I rprsnts th proporton of arcraft n wthn th arport vcnty that hav an ncdnt that causs t to crash, or run off th runway, ct. Th Ι varabl rprsnts th typ of accdnt th arcraft wll hav (.. crash short of runway on approach, or run off th sd of th runway, tc.); A s th probablty that th arplan of class touchs n th landng phas or aborts th tak-off n th dtrmnd pont A; B / A s th probablty that th arplan of class, dpartng from th pont A coms to stop tslf n pont B. { } { } A Fg. - Dscrdtd ara objct of study. Napls Intrnatonal Arport. Addng, for vry pont B, th probablts dtrmnd (4), rlatvly for vry catgory n whch th sampl wll b dvdd, total probablts ar calculatd. Envlopng th ponts charactrzd by th sam total probablty th abov mntond aras w ar obtand. Snc th xamnd accdnts ntrstd dffrnt masurs of runway, to gv a corrct ntrprtaton of th statstc data rlatd to th dstancs has bn ncssary to mak admnsonal th dstancs nformaton. To such purpos w hav ntroducd "standard runway" that has a lngth qual to ft and a wdth qual to 50 ft. Dvdng ths dmnsons for th ral ons of th runways ntrstd by th rlvd accdnts, th valus of two homognzd coffcnts (C x and C y ) hav bn obtand. Multplyng dctats valus for th ral lngth and wdth, may b possbl to dfn th accdnts schms of th "standard runway", on th bas of whch th study has bn conductd. For xampl th /07/00 n Fumcno Rom Arport accdnt has ntrstd a typ MD- arplan. In such cas th runway 6C dmnsons ar ft, of lngth and 50 ft, of wdth. Dvdng ths masurs of th "standard runway" to ths th followng valus of th Cx and Cy coffcnts ar obtand: C x =,05 C y =,000. Multplyng ths dstancs accordng to th x and y axs, and th abov mntond coffcnts w ar obtand som homognzd valus bass of our study has bn conductd. In dtal rsults that th arcraft MD- has touchd th B ISBN: ISSN:

7 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 runway to a dstanc of 94 ft and t s arrstd to 3665 ft from ths. W hav procdd n analogous way for all rlvd accdnts and for vry manuvrs (landng and tak-off). Th modl provds quatons n ordr to dtrmn thr th mpact or wrckag locaton of an arcraft followng an accdnt. Svral quatons ar dscrbd for all prmutatons of: Arcraft opraton (approach and dpartur); Crash from flght, or runway run off; Crash locaton (bfor or aftr th prpard runway surfac. Ths quatons form a st of probablty dstrbuton functons of a crash occurrng pr unt ara. 4.. Th proporton accdnt typ modl Ths approach modl nvolvs th statstcal modllng th occurrnc of ar accdnts ovr tm; a Posson squnc or Posson procss s oftn dployd. Such a procss s basd on th followng assumptons: an vnt can occur randomly and at any tm and any pont n spac. Past arcraft accdnts had ths faturs. Thy occurrd n a random mannr n dffrnt parts of th world; th occurrnc of an vnt n a gvn tm or spac ntrval or sgmnt s ndpndnt on what happnd n any othr non-ovrlappng ntrvals or sgmnts. Ar accdnts, xcpt vry rar md-ar collsons, hav occurrd as th srs of ndpndnt vnts n tm and spac; th probablty of an vnt occurrng n a small ntrval Δ t s proportonal to Δ t and can b calculatd by λ Δt whr λ s th man rat of occurrnc of th vnt. It s assumd constant and qual to λ =, whr T a s th avrag tm ntrval btwn conscutv vnts. Th probablty of two or mor occurrncs n Δ t s nglgbl (of hghr ordr of Δ t ). From mprcal vdnc, Δ t s assumd to b a short prod, th probablty of an occurrnc of mor than on arcraft accdnt wll normally b nglgbl. In Posson procsss th tm ntrvals btwn succssv vnts s xponntally dstrbutd, ndcatng no-mmory proprty n th procss. Ths mans that futur vnts do not dpnd on th numbr or tm of prvous vnts. Ths would logcally sm to b th cas wth ar accdnts. Mathmatcally, lt T b th random varabl rprsntng th tm btwn any two conscutv vnts. Ths varabl s xponntally dstrbutd. Th probablty that no accdnt wll occur n tm prod t s: λ t ( t) P( X t = ) = P T T a 0 (5) whr, X t s th numbr of ar accdnts n tm t and λ s th avrag accdnt rat. Smlarly, th probablty of th occurrnc of at last on vnt n tm t s: λ t ( t) = P( T t) = P( X t 0) = P T (6) Th probablstc assssmnt of accdnts uss a sampl of 0 accdnts ovr th prod Th dstrbuton of tm ntrvals btwn ths vnts s shown n Fg. 3. A smpl calculaton provds an stmat of th avrag accdnt rat: λ 7.85 accdnts pr yar or λ 0.05 accdnts pr day. An analyss of th tm ntrvals btwn accdnts, ndpndnt of arcraft typ, ndcats thy hav bn ndpndnt and xponntally dstrbutd (a χ tst confrms th hypothss matchng th mprcal and thortcal data: ( 0) ( 0) = 6.99; χ = 5. χ χ. χ < Ths offrs confrmaton that th obsrvd pattrn of accdnts can b tratd as Posson procss. Usng th xponntal dstrbuton shown n Fg. 3, t s possbl to assss th probablty of an ar accdnt occurrnc. Rlatv numbr of obsrvaton ,8 0,75 0,7 0,65 0,6 0,55 0,5 0, ,4 0,35 0,3 0,5 0, 4 0,5 0, 6 4 0, Th tm btwn th ar accdnts (days) Emprcal data Thortcal data Fg. 3 - Dstrbuton of tm ntrvals btwn conscutv ar accdnts ( ) If thr s unlkly to b any mprovmnt n safty faturs thn ths dstrbuton can b usd for assssng th probablty of futur vnts. Ths probablty rss ovr tm untl th occurrd vnt. { } 4.. Modl formulaton A to landng phas Dvdd th pont sampl of touchdown n two substs corrspondng to th two C and D classs of arcraft. For ach of ths classs a fxd numbr of touchdown dstanc ntrvals has bn dfnd. In ordr to avod havng mpty ntrvals (condton that corrsponds to a lowr part numbr of ntrvals) or nformaton loss around th form of th functon dstrbuton (condton that corrsponds to an lvatd ntrval numbrs) th numbr of ths ntrvals and thr rspctv amplnss hav bn dfnd through th rlatonshps: k = 3,3log0 (7) n ISBN: ISSN:

8 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 x xmn Δ x = (8) k max wth n total numbr of landngs rlatd to th abov wght arcraft classs. Brngng for th whol sampl and for th sngl wght classs th dstrbuton of th touchdown ponts and ntrpolatng th obtand rsults, t s possbl to vrfy, ρ through th tst of th hypothss, of whch wll b sad subsquntly, that ths ar dstrbutd accordng to a Normal functon of avrag and standard dvaton varyng accordng to th wght class arcraft: xμ f ( x) =, < μ < ; σ > 0 (9) σ π partcularly, as shown n fgur 4 and 5: μ =,0, σ =,79 for th C class arcrafts; μ =,58, σ =,6 for th D class arcrafts. 0,5 0,45 0,4 0,35 0,3 0,5 0, 4..3 Modl formulaton { B / A} to landng phas Also n ths cas to dfn a statstc modl that allows to dtrmn th probablty that an arplan of class stops n pont B, of coordnats (x B ; y B ), aftr havng touchd n pont A of th runway, for vry class of arcraft and for th dffrnt touchdown zons, th stop dstancs wr dvdd along th x and y axs n homognous ntrvals of amplnss qual to: xmax xmn ymax ymn Δ x = and Δ y = () k k wth k = 3,3log0 nj, whr n j s th sampl numrousnss rlatd to th wght class th and to th touchdown ntrval j. Brngng th dstrbuton of th stop ponts along th axl x, rlatvly to th sampl, to th sngl classs of arcraft and th touchdown sngl dstanc ntrvals dfnd abov, th rsults obtand ar shown n Fg. 6. 0,5 0, 0,5 0, 0,05 0,5 0, 0 0,00,60 3,40 5,0 7,00 8,80 0,60,40 4,0 6,00 7,80 0,05 0-7,000-5,800-4,600-3,400 -,00 -,000 0,00,400,600 3,800 5,000 6,00 7,400 8,600 Fg. 4 - Touchdown pont dstrbuton rlatd to th whol wght classs of arcraft Fg. 5 - Touchdown pont dstrbuton rlatd, rspctvly, to th C and D wght classs of arcraft Thrfor th probablty that an arcraft touchs th runway n th pont A s obtand by th followng ntgral: ( A) = x A x x A = xa xa σ π xμ dx (0) For xampl f w would dtrmn th probablty of touchdown for class C arcraft n th dstanc masurng ntrval ft, unforms such dstancs (dvdng for.000), from th prcdng fgur ar drawn that: {,4 x,6 } = { x,6 } { x,4 } = 0,680,37 0, 3. = Dstrbuzon sprmntal Gamma Normal Fg. 6 - Exampl of stop ponts dstrbuton rlatd to th dstancs of touchd by th runway thrshold lssr or qual than th 800 ft and class C of arcraft From an analyss of th obtand rsults t s dducd that th probablstc dstrbuton functon of th stop ponts along th axs x s a Gamma functon: α x x f ( x; = () wth paramtr: α = 6 for th class C of arcrafts and for all th dstancs of touchdown pont A on th runway; α = 8 for th class D of arcrafts and dstancs from A pont lssr or qual to th.000 ft; For th stop ponts far to touchdown mor than.000 ft t s possbl to approxmat, for class D of arcrafts, th mprcal data wth a Normal functon of avrag μ = 8, 05 and standard dvaton σ =,46 xμ f ( x) = (3) σ π Thrfor th probablty that an arcraft stoppd n th pont wth coordnats (x B ; 0) onc touchd n A s gvn from: ISBN: ISSN:

9 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 { / A} = x x α dx (4) for th class C of arcrafts apart from th touchdown pont, and th class D arcraft and touchd dstancs by th thrshold runway lssr or qual to.000 ft. Whl for th class D arcrafts and touchd dstancs by th runway thrshold mor than.000 ft, ths s gvn: { / A} = σ π xμ dx (5) In quvalnt way, th probablts can b calculatd through th followng fgurs as dffrnc of th ordnats corrspondng to th ponts: x A and x A (6) Lkws n y drcton w hav dtrmnd th stop ponts dstrbuton, xprssd by a normal functon: yμ f Y ( y) = σ π (7) wth: μ = 0,856; σ =, 439 for C class arplans and touchdown dstancs lssr or qual to th 800ft; μ = 0,380; σ =, 434 for C class arplans and dstancs of touchdown among to th 800 and th.000 ft; μ = 0,309; σ =, 408 for C class arplans and touchdown dstancs mor than.000ft; μ = 0,48; σ =, 3 for D class arplans and touchdown dstancs lssr or qual to.000 ft; μ = 0,44; σ = 0, 983 for D class arplans and touchdown dstancs mor than.000ft; Thrfor th probablty that th arcraft stops n pont (0; y B ) onc touchd A s gvn by: yb σ { y / A} = dy B yb σ π yμ (8) Fnally th probablty that th C class arcraft stoppd n th B pont, aftr touchng n A pont s gvn from: x α x yb σ { B/ A} = dx dy yb σ π yμ (9) nstad, for th D class of arcraft th abov probablty s changd n: yb σ { B/ A} σ = dx dy σ π xμ yb σ π yμ { } { } (0) 4..3 Modl formulaton A and B / A for tak off phas Followng an analogous procdur to th landng cas, t has bn possbl to vrfy that th dstancs n whch th takoff was abortd ar dstrbutd accordng to a normal functon: xμ f ( x) = σ π, < μ < ; σ > 0 () wth: μ = 5,09 and σ =, 7 for th C wght class of arplan; μ = 5,6 and σ = 3, 7 for th D wght class of arplan. Th probablty functon s: ( x) = xa xa σ π xμ dx () For th probablty functon that dtrmn th arcraft or dbrs stop ponts dstrbuton w hav dtrmnd that thy chang n accord wth Gamma functon: α x x f X ( x) = (3) wth: α = 5 for th C wght class of arplan; α = 4 for th D wght class of arplan. Th probablty functon s: { / A} = x x α dx (4) In y drcton w hav notcd a normal dstrbuton to dtrmn th stop pont n th (y B,0) coordnats rlatd to th abortd tak off n B ponts: yμ f Y ( y) =, σ π < μ < ; σ > 0 (5) wth: μ = 0,050, σ =, 464 for th C wght class of arplan and stop dstancs lssr or qual to ft; μ = 0,48, σ = 0, 90 for th C wght class of arplan and stop dstancs mor than ft; ISBN: ISSN:

10 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 μ =,563, σ = 3, 898 for th D wght class of arplan and stop dstancs lssr or qual to ft; μ = 0,67, σ = 0, 58 th D wght class of arplan and stop dstancs mor than ft and th probablty functon s: yb { yb / A} = yb σ π yμ dy (6) Th probablty that th arcraft stoppd n th B pont, aftr abortd th tak-off manouvr n A pont s gvn as: yb { B/ A} = dx x x α yb σ π yμ dy (7) 4. Rsults analyss Th modl rsult gv us th soprobablstc ponts n whch w dtrmn arcraft or dbrs rlatd to accdnt. If w jon such ponts w dtrmn th crash locaton aras around th arport, as shown n th followng fgur 7. Partcularly n ths rsarch w hav consdrd Napls Intrnatonal Arport wth mx ndx traffc: 68% arcrafts blongng to C wght class; 3% arcrafts blongng to D wght class. If th abov rpartton chang th boundars may b chang. In fact n th probablty dtrmnd wth th modl mplmntd n th prvous paragraph t s hypothszd a rlaton btwn th probablty of th accdnt locaton ( P( B) ) and th mx ndx traffc ( n n ): n = n = (8) n { B} {} I { A} { B A} I / Fg. 7 - Isofrquncy lns around th arport applyng th modl formulaton abov mntond 4.3 Evaluaton of accdnts consquncs In ordr to assss th consquncs of an accdnt s, for dffrnt rasons, rathr dffcult. In th prsnt study w hav proposd as magntud scal that foundd on th numbr of popl n th objct study ara, n rlatonshp to thr prmannc tm. Partcularly w hav dtrmnd th numbr of popl nsd vry accdnt locaton, abov schmatzd, through th product of th housng dnsty, (data ISTAT sourcs) for th xtndd ara. Such valu wth prmannc coffcnt w hav multpld. Ths coffcnt wll b gvn by th rlatonshp of th prmannc tm, n hour, for th fxd popl catgory, nsd th ntrstd ara, and th total hours n th day, multpld for 000; thrfor n th rsdnt cas ths wll b qual to 000, for th studnts t wll b qual to 660; for th mploys 330 (n fact w hav hypothszd that thy rmans for th job tm alon), for th popl on th board n th arcraft w hav hypothszd a valu qual to. Multplyng dctats valus for th rspctv accdnt probablty, dscussd n th prvous paragraphs, th rsk s obtand. 4 Concluson Ths papr has consdrd rsk assssmnt appld to arport runways. Som nw computr basd tools hav bn dscrbd n ordr to support th assssmnt by hlpng n th spcfcaton and valuaton of mtgatng faturs. Wth ths modl w dtrmn th rgon around arport that wll b ntrstd by th ncdnt. In othr words w dtrmn th ara affctd by dffrnt probablty occurrnc of ncdnt (frquncy of occurrnc of a dfnd hazard). In ordr to dtrmn th rsk th magntud functon and th probablty modl (frquncy of accdnt rfrrd to accdnt and th opraton of arcraft typs) ar multpld. Ths modl s a quanttatv tool that can b utlzd both n arport dsgn and n th opratons managmnt, assssng n th frst cas an usful tool to th nfrastructur ralzaton of a gvn capacty n th othr cas a lmt to th arport capacty. Rfrncs: [] AA.VV, GASR Modl Audt Rport Tmplat, WP094, 000. [] AA.VV., Mthod for assssng Thrd Party Rsk Around Arports, Natonal Arospac Laboratory Nthrlands, 00. [3] AA.VV., Assssng rsk and sttng targts n transport safty programms, Europan Transport Safty Councl, Brussls, 003. [4] AA.VV., Statstcal Summary of Commrcal Jt Arplan Accdnts worldwd opratons , Bong statstcs, 003. [5] Ar Transport Acton Group, Th Economc Bnfts of Ar Transport, ATAG, Gnva, 996. [6] Bazargan M., Ross D. L., A Comparatv Rsk Masur ISBN: ISSN:

11 0th WSEAS Int. Conf. on AUTOMATIC CONTROL, MODELLING & SIMULATION (ACMOS'08), Istanbul, Turky, May 7-30, 008 for Gnral Avaton, prsntd at M.C.D.M., Whstlr, Canada, Aug 6-, 004. [7] CAA Safty Rgulaton Group, CAP 7 Safty Managmnt Systms for Commrcal Ar Transport Opratons, Cvl Avaton Authorty, Gatwck, 00. [8] Col J., Ovrvw of avaton safty ssus, Th Svnth Annual Avaton Forcast Confrnc, Natonal Ar Traffc Controllrs Assocaton, Washngton, 997. [9] Corr S.J., Potntal growth n ar travl dmands rnwd ffort to mprov safty rcord. Intrnatonal Cvl Avaton Organsaton Journal Vol.7, No.9, 994. [0] Dos A., Safty s bst srvd by payng clos attnton to th ky lmnts n ts managmnt. ICAO Journal Vol.0, No., 995. [] Erto P., obabltà statstca pr l scnza l nggnra, McGraw-Hll, Mlan, 999. [] Evans A.W., Rsk assssmnt by transport organsatons. Transport Rvws Vol.7, pp , 996. [3] Floyd P., Nwaogu T.A., Salado R., Gorg C., Establshng a comparatv nvntory of approachs and mthods usd by nforcmnt authorts for th assssmnt of th safty of consumr products covrd by th Drctv 00/95/EC on gnral product safty and dntfcaton of bst practcs, Fnal Rport pard for DG/SANCO, Europan Commsson by Rsk & Polcy Analysts Lmtd, Untd Kngdom, 006. [4] Hadjmchal M., McCarthy J., Implmntng th Flght Opratons Rsk Assssmnt Systm, 57th Intrnatonal Ar Safty Smnar Shangha, Chna, Nov 004. [5] Janc M., An assssmnt of rsk and safty n cvl avaton, Journal of Ar Transport Managmnt Vol.6, pp , 000. [6] Kanafan A., Th analyss of hazards and th hazards of analyss: rflctons on ar traffc safty managmnt., Insttut of Transportaton Studs, Unvrsty of Calforna, Brkly, Workng papr, UCB-ITS-WP-84-, 984. [7] Kuhlmann A., Introducton to Safty Scnc. Sprngr, Nw York, 98. [8] Lazarck R., Systmatc Assssmnt of Arport Rsk, NDIA 6th Annual Scurty Tchnology Symposum, FAA Avaton Scurty R&D, 000. [9] Luxhøj J.T., obablstc Causal Analyss for Systm Safty Rsk Assssmnts n Commrcal Ar Transport, n ocdngs of th Workshop on Invstgatng and Rportng of Incdnts and Accdnts, Wllamsburg, Sp 003. [0] Own D., Ar Accdnt Invstgaton: How Scnc Is Makng Flyng Safr. Patrck Stphns Lmtd, Yovl, 998. [] Rason J., A human rror, Nw York, Cambrdg Unvrsty ss, 990. [] Rosnbrg, B., Ar safty: th stat of art. Avaton Wk and Spac Tchnology pp.5-66, 987. [3] Sprggs J., Arport Rsk assssmnt: Exampls, Modls and Mtgatons, 0 th Safty-crtcal Systms Symposum, Southampton, England, 00. [4] Trbojvc V., Lnkng rsk analyss to safty managmnt, PSAM7/ESREL 004, Brln, 004. [5] Tocchtt. A., Infrastruttur d mpant aroportual, Gudo Angl Edtor, 983. [6] Wagnmakrs J.H., A rvw of transport arplan prformanc rqurmnts mght bnft safty, Flght Safty Dgst Vol.9, pp.-4, Flght Safty Foundaton, 000. [7] Wgmann D. A., Shappll S. A., A human rror approach to avaton accdnt analyss: Th Human Factors Analyss and Classfcaton Systm. Ashgat Publshng, 003. [8] Zanll S., Affdabltà scurzza nll ndustra d procsso, Zanchll dtor, 998. ISBN: ISSN: