PROJECT 40 EVALUATION OF CONTINUOUS DESCENT APPROACH IN NORMAL AIR TRAFFIC CONDITIONS PURDUE UNIVERSITY. FINAL REPORT May 31, 2011

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1 FINAL REPORT May 31, 2011 PROJECT 40 EVALUATION OF CONTINUOUS DESCENT APPROACH IN NORMAL AIR TRAFFIC CONDITIONS PURDUE UNIVERSITY Project Lead Investgator Dengfeng Sun Assstant Professor Purdue Unversty 701 West Stadum Avenue West Lafayette, IN Joseph Post Offce of Systems Analyss Federal Avaton Admnstraton Washngton, DC, USA Unversty Partcpant(s) Purdue Unversty P.I. (s): Dengfeng Sun Danel DeLaurents Students Y Cao Tatsuya Kotegawa FAA Award Number 09-C-NE-PU-004 Perod of Performance 09/01/ /31/2011 1

2 Task(s) Studes on feasblty of contnuous descent arrvals under normal and heavy ar traffc.

3 Project Overvew Ths project nvestgates the mpact of Contnuous Descent Approach (CDA) about the nbound traffc n the termnal arspace. The mpact ncludes fuel consumpton and total flght tme savngs. Ths project dffers from other CDA projects n that t evaluates the CDA under normal ar traffc condtons where congested traffc s taken nto account. Flyng a CDA trajectory ncreases the rsk of potental collson as the plot may have less control on the arcraft under near del thrust settngs. Evaluaton of fuel consumpton and flght tme only makes sense when the nbound traffc employng CDA s conflct-free. Safety can be guaranteed by employng conflct detecton resolutons (CDR). Although tactc manuevers, such as headng change, horzontal speed change, and vertcal speed change, are able to solve the most mmedate collson, they potentally nterrupt the near del thrust settngs. Consequently, the CDA trajectory s aborted. In ths project, a strategc soluton s developed whch sequences the arrvng arcraft under mnmum separaton constrants as well as mles-n-tral constrants. In addton to nterarcraft separaton, ths project also takes nto account the mutual nterference between streams flowng nto arports of a metroplex. The fuel consumpton and delay for deconflcton are counted when the fuel and flght tme savngs are evaluated. The proposed CDR s appled to the major arports and metroplex arports n the Unted States. Fuel statstc and flght tme are obtaned from the Future ATM Concept Evaluaton Tool (FACET). By comparng the conflct-free CDA to the conflct-free Step-down approach, the benefts of CDA as well as the assocated trade-off are quantfed. Investgaton Team Dengfeng Sun receved bachelor degree n precson nstruments and mechanology from Tsnghua Unversty, Chna, master degree n ndustral and systems engneerng from the Oho State Unversty, and PhD degree n cvl engneerng from the Unversty of Calforna - Berkeley. Dr. Sun's research areas nclude control and optmzaton, wth an emphass on applcatons n ar traffc flow management, dynamc arspace confguraton, and studes for the Next Generaton Ar Transportaton Systems. Danel DeLaurents s an Assocate Professor n Purdue's School of Aeronautcs & Astronautcs n West Lafayette, IN. Dr. DeLaurents leads the System-of-Systems Laboratory (SoSL) whch ncludes graduate and undergraduate students as well as professonal research staff. Hs prmary research nterests are n the areas of problem formulaton, modelng and system analyss methods for aerospace systems and systems-of-systems (SoS), wth partcular focus on ar transportaton. Hs research s conducted under grants from NASA, FAA, Navy, and the Mssle Defense Agency. Dr. DeLaurents s an Assocate Fellow of the Amercan Insttute of Aeronautcs and Astronautcs, served as Charman of the AIAA s Ar Transportaton Systems (ATS) Techncal Commttee from , and s Assocated Edtor for the IEEE Systems Journal. He earned a PhD n Aerospace Engneerng from the Georga Insttute of Technology (Atlanta, GA) n Joseph Post s the drector of systems analyss n the Federal Avaton Admnstraton's NextGen and Operatons Plannng organzaton. He receved bachelor degree n aeronautcs and astronautcs from the Massachusetts Insttute of Technology, master degree n electrcal engneerng from Yale Unversty,

4 and master degree n economcs from George Mason Unversty. Mr. Post holds numerous patents n the area of automatc flght control systems and s an nstrument-rated plot. Tatsuya Kotegawa s a graduate research assstant n the System-of-Systems Laboratory and a PhD canddate n the School of Aeronautcs and Astronautcs at Purdue Unversty. He receved hs BS and MS n Aeronautcs and Astronautcs Engneerng from Purdue n 2006 and Hs research nterest les n developng foundatonal methods and tools for addressng problems seen n large-scale, complex systems, often characterzed as system-of-systems. Y Cao s pursung the PhD degree at the School of Aeronautcs and Astronautcs, Purdue Unversty. He receved bachelor degree n Instrumentaton Scence and Engneerng n 2006, and master degree n Navgaton, Gudance and Control n 2009 from Shangha Jao Tong Unversty, Chna. Hs research manly focuses on modelng, optmzaton, smulaton, wth an emphass n ar traffc flow management. Task # Task Ttle Project 40 Contnuous Descent Arrval Natonal Operatonal Feasblty Objectve(s) The objectve of ths project s to quantfy the fuel savngs of conflct-free CDAs n normal termnal arspace operatons. Effort s taken to understand what the trade-off would be f current Step-down approach s replaced by CDA. The overarchng goal of ths project s to examne the feasblty of CDA natonally, n partcular to provde a better estmate of the prospectve benefts. Research Approach Due to the hgh cost for feld test, t s mpossble to evaluate CDA natonally by practce. Therefore, a smulaton-based assessment s the only way to provde an ntal estmaton. In ths project, FACET s used as the smulaton platform, whch can smulate and vsualze the enroute traffc as well as the nbound traffc recorded by the ASDI data. FACET has a buld-n arcraft performance database. Usng the nformaton assocated wth a specfc arcraft type, the fuel and flght tme of every recorded flght can be estmated. Moreover, FACET provdes a varety of JAVA APIs enablng one to develop customzed algorthm and ncorporate t nto a smulaton. In order to evaluate CDA, two scenaros are set up. In the frst scenaro, the flght descends along a CDA trajectory; n the second scenaro, the flght descends along a Step-down trajectory. In both scenaros the ground tracks are the same. The only dfference s the vertcal decent profle, whch results n dfferent fuel consumpton and flght tme. Fgure 1 shows a flowchart of the smulaton whch s desgned to obtan the data for beneft evaluaton. Frst, the ASDI data s fed nto FACET. FACET runs n a Smulaton mode where fled flght plans are

5 used n conjuncton wth the arcraft performance database to smulate the traffc. Smulated trajectores are the output from ths smulaton. The sequencng algorthm s programmed n C++, and then the smulated trajectores are processed. Delay assgnment to each flght s obtaned from the sequencng algorthm. The smulaton s run agan where the delay assgnment s also fed nto FACET n conjuncton wth the flght plans. A buld-n conflcton detecton module can verfy whether the traffc s conflct-free. The fuel consumpton and flght tme can be recorded as well n ths smulaton. Mlestone(s) N/A. Fgure 1 Flow chart of smulaton Specfc works nvolved n the smulaton are lsted as follows. 1. Vertcal profle desgn (August ~ October, 2010, completed). By default FACET uses CDA profle to propagate the descent trajectory of an arrvng arcraft. A conventonal Step-down profle must be desgned to provde a baselne. Usng the APIs, all arcraft can be programmed to fly the Step-down trajectores. Wth the Step-down and CDA profles, the fuel and flght tme can be compared. There s no formal defnton for the Step-down approach n lterature snce the trajectory of a Step-down approach s contngent wth varous practcal factors, such as traffc condton n the

6 destnaton arport, arcraft type, wnd and so on. A typcal Step-down approach nvolves the followng elements: (a) The arrvng arcraft start descendng when t reaches the calculated Top of Descent (TOD). (b) There are several level-offs durng the descent procedure. (c) The level-offs are usually between 5,000~10,000 ft, and 20 nautcal mles (nm) dstant from the touchdown. (d) The arcraft ntercepts the fnal 3 ILS glde path at an approprate dstance from the touchdown. In FACET, the poston of TOD s calculated usng the preset arspeed of a partcular arcraft type. In the Smulaton mode, effects of wnd and nterference between arcraft are not consdered. A vertcal profle of CDA s a smooth glde slope stretchng from the TOD to the touchdown. A Step-down profle can be obtaned by modfyng the correspondng CDA profle. Two level-offs are added between 60~70 nm and 30~40 nm dstance from the touchdown, wth each has a length of approxmately 10 nm. To compensate the level-offs, the TOD must start 20 nm earler than t does n CDA. Fgure 2 shows the vertcal decent (?) profles of two arcraft types smulated by FACET. Generally, the hgher an arcraft cruses, the further away ts TOD s from the actual touchdown. For LJ35 whch s a small arcraft, ts cruse alttude s (Is t better to have the real number here?). Thus ts TOD s only 40 nm dstance from the touchdown n CDA, consequently one level-off s added. In case the TOD s too close to the touchdown to accommodate a level-off, no level-off wll be added. Therefore, n the Step-down smulaton, the number of level-off of an arrvng arcraft s determned by the poston of ts TOD n CDA smulaton. Fgure 2 Vertcal profles of two arcraft types n CDA and Step-down approach

7 Fgure 3 shows the fuel consumpton of the A320 presented n Fgure 2. It reveals the secret of fuel savngs by CDA. The upper subfgure compares the fuel flow rate. CDA avods low alttude levels by crusng at hgh alttude as long as possble. The fuel flow rate at low alttude s hgher than that at hgh alttude. Therefore, CDA saves fuel, whch s valdated by the lower subfgure. It s worth notng that the fuel flow rate of a partcular arcraft type s only a functon of alttude n the smulaton, whch s somewhat deal. But the observaton s consstent wth conclusons from other CDA research. Hence, the result provdes a sound estmaton to the realty. Fgure 3 Fuel consumpton of an A320 arcraft 2. Traffc analyss (September ~ October, 2010, completed). Wth the CDA profles and Step-down profles, we are able to assess the mpact of CDA on the nbound traffc. Amongst varous ssues, safety comes frst. We are nterested to know what t would be f current Step-down could be replaced by CDA. In the Smulaton mode, all arcraft stck to ther flght plans and preset performance settngs assocated wth arcraft types. In other words, nter-arcraft nterference s not taken nto account n the navgaton. As a result, conflcts occur frequently. The mnmum separaton between flghts for enroute traffc s 5 nm for horzontal separaton and 1,000 ft for vertcal separaton below FL290, or 2,000 ft above FL290. In the termnal arspace, the horzontal separaton s commonly reduced to 3 nm. However, from the perspectve of ar traffc control, a 5 nm separaton provdes more buffer to accommodate uncertantes n congested traffc. For llustraton purpose, the separaton s generally outlned by a cylndrcal protected zone around an arcraft, as shown n Fgure 4. If the protected zone of two arcraft has ntersecton, a conflct alert s ssued. Fgure 4 Mnmum separaton

8 Fgure 5 shows the smulated traffc n Newark Lberty Internatonal Arport on August 23, 2005, whch compares the total number of conflcton versus alttude. Data shows that flyng CDA leads to more conflcts than flyng Step-down. The number of conflcts s counted n a way such that f two arcraft are n conflct for 5 mnutes the conflct count ncreases by 5. It s observed that the conflct count ncreases as the flght level decreases. Ths s due to the fact that large volume of traffc funnel through the lmted arspace around the vcnty of arport. In both scenaros, arcraft enjoy the free flght where the arrvng arcraft are not subject to any sequencng control when approachng the runway. Consequently, the conflct count becomes very large below FL30. Between FL80 and FL 30 where arcraft level off when flyng Step-down trajectores, the conflct count s lower than that n CDA scenaro. Ths suggests that level-off provdes more space for staggerng the arrvng arcraft vertcally. Replacng Step-down wth CDA would reduce the degree for spacng arcraft. Fgure 5 Conflct dstrbuton n the termnal arspace around EWR on Aug 23, Development of the sequencng algorthm (October ~ January, 2011, completed). The evaluaton of benefts makes sense only when CDA meets the basc requrements of termnal arspace operatons. In ths project, the followng constrants are applcable: (a) The arrvng flow s conflct-free. (b) The runway capacty s respected. (c) Cross-over traffc of Metroplex arports s de-conflcted. The soluton s a sequencng algorthm. An arrvng arcraft s n near dle thrust settng when

9 performng CDA. Any tactc operaton nclnes to nterrupt CDA. Hence, an arrvng flow should be strategcally sequenced such that all arcraft can follow ther preset trajectores and the correspondng schedules. Constraned Poston Shftng (CPS) s an deal conflct resoluton for CDA whch can preserve the contnuous descent trajectores. An arcraft smply delays ts arrval at the termnal arspace to avod potental conflcts. Thus the manpulaton s fnshed before descendng process begns. The focus s how to determne the delay the arcraft need to acheve a conflct-free CDA. An optmzaton method s developed for sequencng the arrvng flow. (a) Constraned Poston Shftng Ths project s focused on conflcts that would occur n the termnal arspace only. Fgure 6 shows the deal pcture of constraned poston shftng. A cylndrcal regon wth a radus R centered n the arport s defned. The termnal arspace refers to the space wthn ths regon. R s determned n a way such that majorty of the flghts ntate the descendng procedures wthn the termnal arspace where they are subjected to separaton constrants. In most cases, R s set to be 180 nm. It s assumed that the flghts are equpped wth the 4-D capable FMSs and able to fly the pre-determned 4-D trajectores. Then each flght can be predcted wth ts descent trajectory when t s stll arborne. Wth the predcted trajectory, t s possble to check potental conflcts. If two arcrafts are predcted to conflct n the termnal arspace, one of them wll be delayed such that ther arrvals are staggered n tme, as llustrated n Fgure 6 (b).

10 a) Conflct detected based on the predcted 4-D trajectores b) Conflct solved by delayng one of the arcraft Fgure 6 Illustraton of constraned poston shftng The sequencng algorthm s developed to fnd the optmal landng sequence whch mnmzes the total delay. An arrvng arcraft set s denoted as A= [ A1, A2, L, A N ]. Intally,

11 arrvng flghts ndependently plan ther trajectores accordng to ther flght plans wthout consderng mutual nterferences. For flght A and A, ther 4-D trajectores wthn the j termnal arspace are of nterest, whch are a dscretzaton of the trajectores: P( t, t ) = [ p ( t, ϕ, λ, h ), p ( t, ϕ, λ, h ), K, p ( t, ϕ, λ, h )] 0 n n n n n P ( t, t ) = [ p ( t, ϕ, λ, h ), p ( t, ϕ, λ, h ), K, p ( t, ϕ, λ, h )] j j j j j j j j j j j j j j j 0 n j j j n n n n where p ( t0, ϕ0, λ 0, h0) s the frst waypont where A arrves at the boundary of termnal arspace at tme t 0, and p( tn, ϕn, λ n, hn) s the last waypont where A fnshes landng at tme t. ϕ 1, λ 1, h 1 s the lattude, longtude and alttude respectvely. The waypont lst s, n n fact, a temporal and spacal dscretzaton of the trajectory wth an nterval Δ T. A and A j j j are present n termnal arspace n tme wndows [ t0, t n] and [ t0, t m ] respectvely. If [ t0, t n] j j and [ t0, t m ] ntersect n some tme wndow [ t, ] [ 0, ] [ j 0, j p tq = t tn t tm], trajectores of these two flghts must be checked for potental conflcts. A conflct detecton functon s defned: tq j j j p q ϕ0 λ0 0 j ϕ0 λ0 0 t= t CD(, j, t, t ) = C( p (, t,, h ), p (, t,, h )) (1) p j 0 f j j j ht ht H C( p( t, ϕ0, λ0, h0), pj( t, ϕ0, λ0, h0)) = j 1 f ( ht ht < H) &&( d < D) (2) 2 Δϕ Δλ d = 2r arcsn sn ( ) + cosϕcosϕjsn( ) 2 2 where r s the radus of the earth. d s the great-crcle dstance between two wayponts computed usng the haversne formula shown n Eq. (3). H and D are the mnmum vertcal and horzontal separatons respectvely. Generally, D = 5 nm. H = 2,000 ft f flghts are above (3) FL290 and H = 1, 000 ft f flghts are below FL290. From Eq. (2), f two arcraft lose separaton on ther wayponts, CD(, j, t, t ) s nonzero. An ntutve method to de-conflct p q the flghts s to assgn delays to one of the two flghts to stagger them. Suppose A s delayed

12 by Δ t, then a delayed 4-D trajectory of A s generated as follows: P( t +Δ t, t +Δ t) = [ p ( t +Δ t, ϕ, λ, h ), p ( t +Δ t, ϕ, λ, h ), K, p ( t +Δt, ϕ, λ, h )] 0 n n n n n Note that P( t0 +Δ t, tn +Δ t) s smply a shft of the orgnal P( t0, t n) n tme,.e., A wll pass the orgnal wayponts wth a delay of Δ t. Due to the delay, the ntersecton of tme wndow changes to [ tʹ, tʹ ]. If the trajectory of the arcraft s suffcently shfted, then, one can p q ensure that[ tʹ, tʹ ] = φ, or CD(, j, t, t ) = 0. Essentally, one can resolve the conflct between p q p q the arcraft by sutably delayng the entry tme of the arcraft nto the regon. The proposed schedulng method s essentally a trajectory-based resoluton whch can be appled to both CDA and Step-down. In a busy traffc envronment, delayng one arcraft may result n addtonal conflcts wth other arcraft. The objectve s to determne the mnmum delays needed to de-conflct the nbound traffc. Such problems can be formulated as a Mxed Integer Lnear Program (MILP). (b) Mxed Integer Lnear Program Formulaton Defne a decson varable vector for each arcraft: w = [ w, w, K, w ], {1,2, K, N} (4) 0 1 L where w s a bnary varable. k w means there are L possble delay solutons assgned to A, each wth a delay of kδ T. If A s assgned the th k delay, k 1 w = ; other decson varables assocated wth A are zero. The maxmum delay allowed s LΔ T. The goal s to mnmze the total delay. The objectve functon s as follows: N L mn cwk k ΔT (5) = 1 k= 0 The objectve functon shown n Eq. (6) s the weghted delay. c s the weght gven consderaton to the farness among flghts. If the objectve s to mnmze the fuel consumpton, c can be set to the fuel flow rate. The objectve functon s subject to: L wk = 1 (6) k = 0

13 w {0,1} (7) k f ([ t, t ] φ && CD(, j, t, t )) p q p q then set: w k j + w 1 kj (8), j {1,2, K, N}, k, k {0,1, K, L} Eq. (7) means each flght can only be assgned to one delay soluton. Eq. (8) s the bnary constrant. Eq. (9) s the conflct detecton constrant. Suppose two flghts are assgned delays k j Δ T and kjδ T respectvely ( w k = 1 and w = 1). Then ther delayed 4-D trajectores are checked. If there are conflcts, Eq. (9) guarantees that such assgnment s nfeasble. Essentally, the algorthm enumerates all the possble delay assgnments, and uses the MILP to determne whch one leads to the mnmum cost. The maxmum amount of delays L s crtcal to the exstence of a feasble soluton. If L s too small, t s not able to separate arcraft n conflct even wth the maxmum delay. If L s too large, there must be a feasble soluton (n the worst case, flghts are sequenced to fly nto the termnal arspace one by one). However, the dmenson of the problem could grow to an extent that t may be very dffcult to solve computatonally. Hence, to search for a mnmum feasble delay assgnment, we start the smulaton by choosng a small value of L ( 10 ). If the optmzaton s nfeasble, the algorthm ncreases L by 1, and starts a new run. The algorthm does not stop untl there s a feasble soluton. (c) Mnmum n-tral separaton The schedulng algorthm solves conflcts durng the descents, but t does not evaluate the arrval capacty of the arport. Each arport has a maxmum capacty whch vares upon runway confguratons and local terran. The arrval flow must be sequenced to meet the capacty bound by requrng a mnmum n-tral separaton between successve arrvals. For example, the typcal benchmark rate of EWR s 40 landngs per hour, whch s equvalent to 1.5 mnutes per landng. The fnal soluton must guarantee that the landng ntervals are not less than ths mnmum n-tral separaton. One more step s added to accomplsh ths after obtanng the delay assgnment for CDA separaton. k j j By the schedulng algorthm, the landng tme of A s obtaned: L landng n k k= 0 t = t + w kδt Wth delays, the flghts arrve n a new order. Frst, the new tme of arrval t are sorted n landng a non-decreasng order usng the Bubble Sort algorthm. Then successve arrvals are checked

14 for the mnmum n-tral separaton. Suppose that A lands next to A : j f ( t t <ΔT ) j landng landng mn. n tral t = t +ΔT j landng landng mn. n tral where Δ Tmn. n tral s the mnmum n-tral separaton measured n tme. Ths process fnally produces another new arrval sequence that respects both the conflct separaton constrants and arrval rate constrants. The complete algorthm s lsted n Table 1. Table 1 Sequencng algorthm Fgure 7 shows the arrval wth and wthout n-tral separaton; JFK encounters hgh traffc between 20:00 and 24:00 when the arrvals are nearly twce as the benchmark rate. Ths accounts for the hgh amount of delays that JFK receves. The arrvals are so ntensve that

15 many flghts have to be delayed before enterng the termnal arspace and wat for landng servces. EWR and LGA do not encounter such a burst durng the peak hours. But EWR has a hgh level of traffc above the benchmark rate, thus t needs a hgher amount of delays to control the arrval rate than LGA. Fgure 7 Arport arrvals wth n-tral separaton a) Sngle arport b) Metroplex arports Fgure 8 Cross-over traffc n metroplex arports

16 (d) Practcal concerns For long dstance flght, arcraft generally begn descendng 150 nm dstant away from the touchdown arport. Delay control must be effectve before descendng. Therefore, the affected traffc covers a vast area. Fgure 8 (a) shows the arrvng flows around EWR. The yellow crcle has a radus of 180 nm and covers a vast area. Arrvng flghts flow nto EWR manly from three drectons. The flght courses wthn the crcle are subject to be optmzed. Fgure 8 (b) shows the arrvng flows around EWR, TEB, JFK and LGA n New York Metroplex. Obvously, arrvng flows of dfferent arports nterlace wth one another. Not only should the flghts flyng to the same arport be sequenced, but also the flghts belongng to dfferent flows be staggered n tme. Therefore, the nbound traffc of metroplex arports should be sequenced as a whole. In ths project, sx metroplexes are chosen (see Table 2), whch ncludes a subset of the major arports n the contnental Unted States. Table 2 Metroplex arports Metroplex Arport Code New York Texas North Calforna South Calforna Washngton DC Chcago EWR, JFK, LGA, TEB SAT, AUS, IAH, HOU SFO, SJC, OAK, SMF LAX, ONT, SAN BWI, IAD, DCA ORD, MDW The algorthm can schedule a whole day s traffc. But n real mplementaton, the plannng tme horzon s dvded nto several tme wndows, and then each wndow could be represented by an ndependent optmzaton problem. Ths s due to the fact that ar traffc managers generally look nto traffc of 4 or 6 hours ahead. In practcal settngs, t s dffcult to predct the trajectory of an arcraft before ts departure or long before ts arrval. Therefore, dvdng the whole day nto 6 4-hour tme wndows s more close to the real operaton. Furthermore, comparng the traffc by tme makes the optmzaton easy to solve as each tme wndow nvolves only a subset of arrvng arcraft of a day. If an arcraft s delayed and pushed nto the next tme wndow, ts schedule wll be frozen. But the optmzaton of the next tme wndow must take ts presence nto account, that s, other flghts smply check wth t for potental conflcts. If there are predcted conflcts, the other flghts are delayed. 4. Benefts and tradeoff analyss (January ~ Aprl, 2011, completed): The objectve arports are 26 major arports plus the sx metropolex arports. Bascally, the selected arports contan 40 major arports whch covers majorty of the nbound traffc n the contnental Unted States. Hence, ths project evaluates CDA on a natonwde bass. For the 26 arports, the nbound traffc n each arport s sequenced ndependently. For the metroplex arports, the nter-flow nterference s taken nto account. The flght plans are provded by the ASDI data on August 24, All trajectores are tracked wth a 1 mnute nterval. The proposed sequenced

17 algorthm s appled and statstcs are obtaned based on the smulated conflct-free traffc. (a) Delay The conflct-free CDA s acheved at the expense of delayng a set of arrvng arcraft. Table 3 presents the delay statstcs of the 26 major arports and the sx metroplexes. It can be concluded that flghts flyng CDA are more dffcult to sequence by comparng the Total delay and Max delay. In most arports, CDA has hgher value than Step-down n these two terms. Over all, CDA ncurs 25% more total delay than Step-down. Meanwhle, the maxmum delay ( L ) for the ndvdual arcraft also suggests that CDA leads to hgher delay. Ths observaton s consstent wth prevous clams. CDA does not lend tself to staggerng arcraft n space. As a result, t needs hgher delay to stagger arcraft n tme. Table 3 Delay generated by the sequencng algorthm CDA Step- down Arport AC No. Max delay (mn) Total delay (mn) Max delay (mn) Total delay (mn) ATL BNA BOS CLE CLT CVG DEN DFW DTW FLL IND LAS MCI MCO MEM MIA MSP PDX PHL PHX PIT RDU SEA SLC STL

18 TPA New York Metro Texas Metro North Cal. Metro South Cal. Metro Washngton DC Metro Chcago Metro Total (b) Benefts and tradeoff Delay generated by the sequencng algorthm can be absorbed by ether ground delay or arborne delay. From a perspectve of fuel economy, ground holdng saves more fuel as there s no unnecessary fuel burn for arborne delay. However, ground holdng program postpones departures at the orgn arports. Delayed arcraft may not be granted departure tme slots at a later tme durng busy hours so that longer delay mght be enforced. In contrast, arborne delay s more flexble, but more expensve as well. Fgure 9 shows the delay dstrbuton n New York Metroplex arports. It can be seen that most of the delays mposed on the arrvng flghts are less than 5 mnutes n ether CDA or Step-down. Thus the delays are easy to absorb by arborne delay. Both delay strateges are smulated and compared n terms of fuel consumpton. The results are summarzed n Table 4. Fgure 9 Delay dstrbuton n the New York Metroplex arports

19 The fuel savng of an arport s the fuel consumpton dfference between the conflct-free Step-down and the conflct-free CDA. From Table 4, t s observed that Ground delay leads to hgher total fuel savng as t avods the extra fuel consumpton due to delay. The savng s proportonal to the arcraft number. The buser the arport, the hgher the total savngs could be. The flght tme savng s the flght tme dfference between the conflct-free Step-down and the conflct-free CDA n the termnal arspace where delay s not counted as t s mposed outsde the termnal arspace. The flght tme savng s a consequence of avodng low alttude level-off. CDA keeps the arcraft crusng at hgh alttude as long as possble. The arcraft stay n hgh speed settngs for longer. Table 4 Total fuel and flght tme savngs by arports Arport AC No. Fuel saved/kg (Arborne delay) Fuel saved/kg (Ground delay) Flght Tme saved /mn ATL BNA BOS CLE CLT CVG DEN DFW DTW FLL IND LAS MCI MCO MEM MIA MSP PDX PHL PHX PIT RDU SEA SLC STL TPA

20 New York Metro Texas Metro North Cal. Metro South Cal. Metro Washngton DC Metro Chcago Metro Total Average Fgure 10 shows the average savngs. In Fgure 10 (a), t can be seen that the fuel savngs are between 20 kg/ac and 60 kg/ac. Table 4 shows that CDA saves 31.09~39.11 kg/ac n average. IATA has reported 50~200 kg fuel savngs per flght by flyng CDA. The estmaton from the smulaton s wthn the confnement. It worth notng that large arports, such as ATL, DFW, and Chcago Metroplex, have hgher average fuel savng. Ths s due to the percentage of arcraft type n the total arrvng arcraft, whch wll be analyzed later. In Fgure 10 (b), the flght tme savng s between 0.5 mn/ac and 1.5 mn/ac. The mean value s 1.01 mn/ac. The extra delay per flght due to flyng CDA s also presented. It s the dfference between the average delay of CDA and the average delay of Step-down. The extra delay can be deemed as the tradeoff of replacng Step-down wth CDA. Compared to the average flght tme saved, such trade-off s mnor. Therefore, CDA s stll benefcal. Comparng Fgure 10 (b) wth Fgure 10 (a), one may fnd that the profle of the bars are smlar, that s, the more flght tme s saved, the more fuel s saved. Ths s consstent to the common sense Average fuel savngs (kg/ac) Arborne delay Ground delay ATL BNA BOS CLE CLT CVG DEN DFW DTW FLL IND LAS MCI MCO MEM MIA MSP PDX PHL PHX PIT RDU SEA SLC STL TPA New York Texas North Cal. South Cal. Washngton DC Chcago a) Average fuel savngs

21 Avgerage \lght tme saved (mn/ac) Flgth tme saved Extra delay due to \lyng CDA ATL BNA BOS CLE CLT CVG DEN DFW DTW FLL IND LAS MCI MCO MEM MIA MSP PDX PHL PHX PIT RDU SEA SLC STL TPA New York Texas North Cal. South Cal. Washngton DC Chcago b) Average flght tme savngs Fgure 10 Average savng statstcs Fgure 11 presents the average fuel savngs as a functon of arcraft type, whch s obtaned from the natonal statstcs. There are over one hundred dfferent arcraft types landng n the US n a whole day, t s trval to check the fuel savngs n terms of specfc arcraft type. We categorze the arcraft by ther szes whch are defned by FAA. It can be seen that the larger the arcraft sze s, the more fuel the arcraft saves. Ths s due to the hgher fuel flow rate of larger arcraft. Heavy arcraft consumes fuels more than twce of Large arcraft does. However, Large arcraft accounts for 77% of the total arrvng arcrafts and contrbute to 61% of the total fuel savng. Therefore, the average fuel savngs of an arport s determned by two factors- the arcraft type and the correspondng percentage. Fgure 12 exemplfes ths speculaton. JFK acheves an average fuel savng that s over ten tmes more than that of TEB. Observng the percentages of arcraft types, one may fnd that Large arcraft accounts for roughly the same percentage n both arports, but t s the Heavy arcraft that contrbutes to the huge dfference. Heavy arcraft accounts for 43% of the total arrvng arcraft n JFK whle Small arcraft accounts for 53% of the total arrvng arcraft n TEB. Therefore, applyng CDA to the bg arports wll receve sgnfcant benefts.

22 kg/ac Average fuel savngs by arcraft type Ground delay Arborne delay Heavy Large Small Arcraft type a ) Average fuel savng versus arcraft type Total savng by arcarft types Small 1% Arcraft types percentage Small 10% Heavy 13% Heavy 38% Large 61% Large 77% b ) Percentage of arcraft type and correspondng contrbutons Fgure 11 Arcraft types

23 kg/ac! JFK 85.1 Ground delay Arborne delay 7.1 TEB 3.1 Fgure 12 Fuel savngs and arcraft type percentages Major Accomplshments Ths project concentrates on quantfyng the benefts and trade-off of employng CDA n the normal ar traffc condton. A sequencng algorthm s proposed targetng at achevng a conflct-free traffc for evaluaton. In a smulaton cycle nvolvng 26 major arports and sx metroplex arports, conflct-free CDA and conflct-free Step-down are both smulated. By analyzng the statstcs results extracted from FACET, we can come to the followng conclusons: a) If current Step-down approach s replaced by CDA, there s great potental to decrease the fuel consumpton and total flght tme n the termnal arspace traffc. The benefts ganed would be sgnfcant for major and metroplex arports gven wth large volume of nbound traffc. b) The fuel savngs has tght connecton wth the arcraft type. Heavy arcraft has the hghest savngs whle Small arcraft has the lowest. Large arcraft contrbutes most to the total fuel savng whle Small arcraft does the least. Mostof the arrvng arcrafts n the objectve arports are Large sze. c) As a trade-off, CDA nclnes to ncrease the dffculty of sequencng the arrvng flow. Because t has lmted degree for the arcraft to be spaced compared to conventonal Step-down approach. But at the same tme, the drawback of employng CDA s to ncrease the delay for de-conflcton purpose. d) Constran Poston Shftng s effectve n schedulng the arrvng flows. It solves predcted conflcts wthout changng speed and flyng drecton, CDA profle s thereby preserved. Although the smulaton gnores some practcal consderatons, such as weather, wnd, and many other factors, t provdes the decson maker wth a reasonable estmaton of benefts and trade-off brought by CDA. Publcatons/Presentaton/Conferences Cao, Y., Kotegawa, T., Sun, D., DeLaurents, D., Post, J., "Evaluaton of Contnuous Descent Approach as a Standard Termnal Arspace Operaton," 9 th USA/Europe Ar Traffc Management Research and Development Semnar. Berln, Germany, June 14-17, 2011.

24 Cao, Y., Rathnam, S., Sun, D., "A Reschedulng Method for Conflct-free Contnuous Descent Approach," AIAA Gudance, Navgaton, and Control Conference, Portland, Oregon, USA, Aug 8-10, Awards N/A. Transton of Research Results N/A. Plans for Next Perod N/A