Document
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__ NASA Technical Memorandum 85652
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: : " FACTORS INFL UE NCING A IRC R AFT
:. GROUND HANDLING PERFORMANCE
/ ; • _:,, ( _I S A-TH-dS b SZ) I ' & CTO R 5 INFLUENCING H8 3 -27979 _, : 32 , p [ _ C A O 3 / _ t X & O I C . 5 _ ,_- U IC " :' " " Un¢las G3 / O 5 2 807q
Tho mas J. Yag e r
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o : JUNE 1983
-.. National Aeronautics and :_ Spa c e Admin = s t ration •. langley Res earch Center Hampton , Virginia23665 FAC T ORS INFLUENCINGAIRCRAFT GR OUN D HANDLIN G PERFORMANCE T. J. Yager, Aero-Space T echn o l o gist r_SA LangleyResearch Center Hampt o n,Virginia A b s tract • P r o bl e m s a ss o c i a t ed with aircraft g r oun d handling o p e rati o n so n w e t r un w a y s ar e discus se dand m aj o r factors which influ e nc e tir e / runwaybraking and cor - ne rlng traction capabilityare identifiedincludingrunway characteristics, tire hydr o planing,brake sy s tem an o malies,an d pil o t inp u t s . Re s earch re su lt s from studies conductedat the LangleyAircraft Landing Loads and Tracti on Facility, testswith instrumented gr ou nd vehicle s and aircraft,and a recent aircraftwet runway accident investigation are summari z edt c indicate the effectsof differentaircraft,tire, and runway parameter s . Several pr o mi s ing means are describedfor improvingtire / runwaywater drainage capability, brak e system e fficiency,and pilot traini n g to hel p optimize aircraft trac- tion performanceon wet runways.
Introd u ction Research findings and tech n ological advances in recent years have helped alleviate,but not eliminate,the ha z ardsassociatedwith adverse weather aircraft o peration s . Conversely,better avionics,growth in aircraft fleet, airp o rt / runway congesti o n,and economicsare fact o rs which have increase d the frequencyof aircraft ground operation s dur i ng inclementweather. How- ever, to a pilot, happinessis still landing into the wind o n a l o ng, clean, dry runway keeping to a minimum the number of challengingsituationswhich • - can arise du ring operationson slippery runway s with fluct u atingcr o sswinds.
Improvementsin aircraftbraking systems, pil o t simulatortraining program s , " and runway surface treatmentshave tended to increasesafety margins but -- weather-related aircraftaccidentsstill occur such as those last year at I Washington,D.C., Boston,and New O rleans. Unpre d ictableand rapidly r I n n _ INAL PAG E I _ ':. OF POOR QUALI I " _ . 2 % changing weather c o n d iti o nst h at may be e nco u nteredat a given airp o rt f u r t h e r . _ c omplicatet h e pr o bl e ms ass o ciatedwith aircraft take o ff an d landing, mane u vers w-J ,_ • : F o r groun d o p' : rations under varying rainfall conditions,a large number of f.
.- interactingrunway, aircraft,and atmosphericvariables,along with pilot ,_ "" tech n i q ue, co mbine t o infl u ence the l ev el o f aircraft runway performance. A ..
_ need ex ists f o r tim e ly recognitionand proper assessmentof these parameter c o mbinationsthat can pro d uc e inadequateaircraft braking and d irectional ._ , " con tr ol pe rf o rmancef o r a given wet runway situatio n .
i !_ ........ W.it_ £h e in±r o .d u ctt o _ . _f larvae and fast jet transp o rtsint o airline ser- _ vice in the late 1950's, various research efforts 1 to 27 have been directed towards evaluatingthe effects on aircraft runway performancedue to differentrainfall rates, runway characteristics, tire features,and brake system operationalmodes. Findings from studiesconducted at the Langley L Aircraft Landing Loads and Traction Facility,tests with instrumentedaircraft 2 and ground vehicles,and a recent aircraft wet runway accident investigation are discussedin the followingsectionsof this paper. In addition to showing .i the effects of s_veral pavement factors and defining the principal causes of , ° : '; wet p avement tire friction degradationand brake system performanceanomalies, severa l pr o misingap p r o achesare identifiedto help retain adequate tire / 2: : _ pa v em en t frictionand brake system efficiencyduring aircraft ground opera- . . .
ti o ns o n wet runways.
PavementFactors ' , _ Water Depth _ The major factorsaffecting aircraftwet runway performanceare identified "._" in fi g ur e 1. This fi g ur e indic a t e s that runway water de p th and tire / pav e ment , drainagecapabilitycombine to define the frictioncoefficientavailable to _,_ . ; _ help meet the aircraft stoppingand steeringrequirements. For low rainfall : ORI O lNA[ P A O E I S OF POOR QUALITY rates a nd g ood d rainage c o n d i t ion s th i s availab l e tire / pa v ementfricti o n c o efficientmay remain high; however, f o r high rainfa ll rates and p oo r drainage c o n d iti o ns,the availab l efricti o n c o efficientcan dr o p drastically, especiallyat the higher aircraft gr ou n d s pee ds . T o help pr o m o tewater drainage,most runways are constructe d with a cr o ss slope o r cr o wn an d c o ars e , h i g h l y te x tur ed _urfac e fi n i s h es are applie d . In general, runway water buil d up o r surface fl ood ing that o ccurs d uri n g periods o f precipitati o n is directly relate d to the rainfa ll i nt ensity,the surface macrotext u re (c o arse,large-sca l e, s urfaceroughness),the runway cr oss s lo pe, an d t o s o me extent, the magnitu d eand directionof s urfacewin d s. Pavement fl oo ding i s define d a s the depth of water that c o mple te lyc o vers the top of all surface asperities. Surfacewin d s have been found to affect water d rainage pa t h lengths in the flo o ded portions o f the runway an d , depen d ing up o n the win d magnitu d ean d direction,the amount of s urfacewater can change fr o m that occurringon a calm day. 1 3 From data c o llec t ed during a c o mprehen s ive Texas Transp o r t ati o nIn s titutestudy described in reference 1 0, a relation s hip was e s tablishedbetween rainfal l intensity, s urface macr o text u re,paveme n t cross sl o pe, an d water drainage path length with o ut the pre s ence o f surface win d s. This relationship,given in figure 2 , can be use d to calculatethe rainfall intensityre q uire d t o initiate fl ood ing in typiual aircraft tire paths on a runway surface for a calm d ay.
The d ata sh o wn in figure 2 repre s entthe calculatedvariati o n in rainfal l rate required to flood t o within 4.5 7 m (15 feet) of the runway centerline.
The main gear tires of a B- 7 6 7 tran s p o rtairp l ane woul d be n ear thi s d istance fr o m the runway centerlineif the airplanewas traveling d irectly down the center l ine. Calculati o nswere m_de for five differentcr o ss sl o pes each having a simi l ar range of macr o texture d e l, ths. In g_neral, the figure sh o ws ORIGINAL PAGE IS .OIE . POOR qUALITY the increasein rainfall rate nee de d t o f l o od the su rface as a f u nc t i o n o f cross slope and macrotexturedepth. If the depth of pavement macrotexture is small, such as observed in some rubber-coate d runway touchd o wnareas, rainfall i n tensityre qu ired f o r flooding is low despite appreciablecross I slope values. Similarly,the chance of reaching flooded surface conditions for a given rainfall intensityincreaseswith decreasingcross slope. In addition, it can be shown that as the distance from the runway centerline (apexof crown) increases,lower rain rates may produce surfacefl o oding.
Texture Various research studies 28-30 have identifie d %wo distinct texture classifications, namely, micro- an d macrotexture, _ In general, microtexture consistsof the fine, small-scale,surfacefeatures such as those found on individualstone particles,whereas m_ , crotexture encompassesthe coarse, large-scale roughnessof a pavementsurface-aggregate matrix. Under rain- fall conditionssufficientto initiatefloodingon runway surfaces,the bulk water drainage effectivenessof the surface is dependenton macrotexture characteri s tics. Based on numerousmacrotexturedepth measurementstaken during several research programs 9 and 28 on a wide variety of runway pavementtypes and conditionsusing both the grease sample and sand patch measurementmethods, surfaces have been classifiedinto the five major pavementgroups or classes shown in the table of figure 3. A general descriptionof the differentcategorizedpavement types is given with class I pavement surfaceshaving the highest macrotexture d epth values and class V surfaceshaving the lowest macrotexturedepth values. Since the potential for dynamichy d roplaning,which is described in the tire friction perform- !
ance section,varies inverse l ywith surfacemacrotexture,c l ass I pavements are identifiedas having the least hydroplaningpotenti_lwhereas class V -" E_.. ; . .r r '_l ,' _I_: : l )g _'t_ OR QUt * Li T Y 5 , ' .- p a ve m e ntsare c o nsid e re d t o b e the m o st susce p tible. Using t h is p a v ement - classificationsystem as a guide for runway surfaces,airport operators should ,- . be e nc ou rage d t o in s tallclass I or II pavement surfaces o n runwaysand if - p e riodicma c rotexture de pt h me,_surements indicate the runway surface is approachingth e cla s s I V category,correctivesurface treatments,such as - ' gr oo ving or rubber rem o val pr o grams, shoul d be implemente d . It is also recomme nded that if a runway or portion of a runway surface is determine d ; t o be within c'a ss IV or V, ade q uatea n d timely notificati o n s h o uld be given " / _- ..... t o pil' o ts particularly during wet weather aircraft lan d ing an d take o ff '.' . op erations.
l vi: A lth ough cla ss I p a ve me n t s ha ve b e en p ro ve n t o minimize wet runway :_ , , frictio n p robl ems ,one recent runway installationcreated another problem • -._ . under dry surface conditions which has since restricted aircraft operations ,: to takeoffsonly. The photographsin figure 4 illustratethe extent of a ' : tire trea d abrasi o n problem which occurre d during three aircraft lan d ing , t es t s on an asphalt-rubber chip seal o verlay surface. This operationalprob- "!.',. lem is attributed to the sharp, multi-e d ged, exposed, st o ne chips use d in - the ov erlay m ix combined with the relativelylow dry surfacefriction ' , 7 .....
," ..... ca p ability.
: ; Contami nants 1 -" L • • ,: Th e e ffect o f s urfac e water an d rubber contaminantson vehicle stopping .i_ ca p abilityan d tire friction performanceis shown in figure 5. This eval- "_. uation was performed with the I_SA-devel o ped diagonal-brake d vehicle (DBV) :. s ho wn i n t he ph otog raphi n fi gu re 5. The brake system d iagram illustrates _j,_ t h e m od ificationma d e to implementstable and controlledvehicle perform- ance during the friction measurements at high speed with two diagonalwheels locked and the remainingpair free rolling (unbraked). The DBV wet / dry
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stopping d istance ratios depicted in the bar graphs for differentrainfall J - !
......., . ........... _ ........... _ ._'--'_y .......................... __ m... . . -_,. , , ._ ...... ., ._ ................ _ ,. . , ; ORIGINAL PAGE IS : OF POOR QUALITY : 6 ratesan d surface typ e s w ere o btaine d fr o m test runs c onductedat t h e same distance off runway centerlinewith brake applicationspe e d from 98 kFa / h " ; (60 mph ) d ow n t o a complete stop. Measurementsof s urfacewat e r d e pth an d • DBV st o pping distance during d ifferentperiodsof rainstormactivity on an , . u n g r oov e d co n crete r u nway with a I percentcrown reveal a direct relation- i • " . ship b e tweena v erage water depth and stopping distance, As rainfall rates increase,greater water buil d up on the runway surfa c e occurs which d ecrease s '. tire friction pe rf o rmanceas reflectedin the increasedDBV wet / dry stopping -" distance ratios. A further increa s e in runway slipperiness wa s f o und near " ._ . the e nd o f th e runway which w as contaminatedby rubber depositedduring • aircraft tire spi n-u p f ol l ow ingt ouc hd o wn. Th e b u il du p o f t he r u b be r co ating ._ .
_ - on runway surfaces tends to reduce pavement texture and hence, dee , "ade tire o frictionparticularlyunder wet conditions. The cross-hatchedDBV stopping - -. distance incrementshown in figure 5 illustratesthe effects of rubber contaminationon the ungroovedconcrete runway slipperiness measurementsfor . differentrainfall rates. Also included in the figure are comparableDBV • - m e a su rements m a de on o th e r gro oved and ungroovedrunways under artificially - wetted (truck)con d itionswhere the average water d epth was 0.5 mm (0.02 in.).
, The longer DBV wet / dry stoppingdistance ratios measured on the ungrooved asphalt runwayscompared to the concrete surfacesare the re s ult of l ower "_i s u rfacemacr ot exture. Fo rtunately,successfulmethods 31 have been developed , : t o rem ove th e rubber depo s it s on runway surfaces using high pressurewater c . . -_-J no w-_a p __ airports reg ul arlysch e d a l _ -runw_ y - _'ob t _e_ " rel_o9_ l tFeat-' "" ments.
' Tire Friction Performance Vi scous and pynamic HYdr g p]aning : i During aircraftground operationsin wet weather, a w ater remova l or J drainage problem is createdat tire / pave m entinterfaces. The runway surface i'
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* " " OR ;C ff t, _ : L r , : , / , I,_ ';' water enc ou nter e dby the m ov ing a l rcraft tires must b e rapi dl yexpe ll e d fr o m T , ,._. : • th e t i re / pa v ement co ntactar e a o r the v isc ous and dy n am i c water p re s s u r e s " that build u p with increasinggr o un d spee d will sig n ificantlyreduce tire " f r_ c tion p erf o rmance. Research s t ud ie s 2 8- 30 ha v e sh o wn t h at th e s lop e o f a tir e friction-speed gra d ient curve is primarilya f u ncti o n o f the s u rface - " _cr o texture, an d the magnitu d e of the fricti o n at a gi v en spee d is relate d r- : ' ; : t o t he su rfac e ml c rotexture. Hence, an assessmentof both surfacemicro- an d .'. _ n acr o texture characteristics i s ne c ess aryt o f ull y r el ate tire fricti o n "_ pe rformance to pavement text u re.
T h e pri nci pa l f o rm s o f th ese w e t p a ve ment tire fri c t ; on losses , n am ely , c v i scous a n d d y n amic h ydr o planing an d r e v e rted rubb e r skid d i ng ,are ill u strated . :. i n figure 6 . T he spe ed regime, pavementand tire con d ition,and tire operating T mo d e that contributet o loss in tire friction are identifie d togetherwith :-"_ the fact o rs that tend to alleviate their occurrence. Viscous hy d r o planing :'. or thin-film lubricationresults from the inabilityof the tire to penetrate "_ and disrupt the very thin residual fluid film left on the pavement after the .. maj o rity of the trapped water has been displace d fr o m the tire f oo tprint.
= ' _ I n t his cas e , the pre s surebuildupwithin the tire / pavementinterfaceis due t o fl u i d v i scous p r ope rties. Sm oo t h tires ope ratingon wet smooth pavements ' T - are particularlysu s cep t ib l eto this type of tire hydroplaning.
- During d ynamic hy d r o planing, a buildup o f hy d r od ynamic pressure between _ . " tire an d fl ood e d pa ve me n t o cc u r s a s the s qu are o f v e hicle speed. 2 When this .... hydro d ynamic pressure excee d s the tire-pavement bearing pressure, a we d ge o f , water penetratesthe tire contact area and the tire fo o tprint is partially . : o r t o tally d etache d from th e pa v e m ent s u rface. Under total dynamic hydro- C, . _ planing c ond itions,tire friction capabilityis re d uced to near zero because " of the inability of the flui d to support significa n t shear force s . It s hould £'f
OR l ell' At. p AG E IS
p OOR qU ALiTY e
be note d that f o r man y w et p a ve r _nta i rcraft 4._peratlons, re d u c p .d tire f r i c ti on performancemay occur fr o m both viscousand dynamic f l uid pressurebui l dup resu l tingin c o mbined visc o us / dynamic hydroplaning. 1 3 The c o ntact pressuredeve_. o ped between tire tread and pav e ment establishes t i le escape velocity of bulk wate - drainag e from beneath t i le tire f oo tprint.
High pressure tires can expel surfacewater more readily from the footprint that low pressure tires. When the aircraft ground spee d equals or exceeds the escape velocity of water drainage fr om the footprint,choked water flow occurs. The tire has now reached th e state of total dynamic hy d roplaning.
Test results 2, 12, and 1 3 indicatethat the critical aircraft groun d speeds required for this total hydroplaningcondition to occur on flooded (runway water depth is greater than tire tread goove depth) pavementswith an unbraked tire are approximately: Spin-down (Rotatingtire) speed, knots = 9 _ / InfIL pressure,psi and Spin-up (Nonrntatingtire) speed, knots = 7.7 _ / infl.pressure,psi For the nonrotatingtire case (as at aircraft touchdown),Langley track test results shown in figure 7 illustratethe delay in tire spin-up following touchdownon a flooded surface until the test carriage speed decreased to approximately93 knots. It is importantthat pilots be aware that the lower hydroplaningspin-up speed, rather than the high hydroplaningspin- down speed, representsthe actual tire situationfor aircraft touchdownon flooded runways.
Re v ert ed R _ ubber_ S _k i_d ding The third form of tire friction loss, rewrte d -rubber skidding, is named for t i le appearanceof the tire tread skid patch after a prolonged locked- J wheel skid. It is believed that friction-generated heat within the skidding I tire / pavementcontact area is sufficientto produce stealn a nd cause the tire _._ _ " _ ....... i .... ___ _" _-" • . . --" i ¸ ......
i" tr e ad r u bber t o revert ba c k to its un c ure d state. 12 and 18 T he so f t gunwn y :_ re v erted rubb e r f o rms a seal aroun d the tire footprint p eri p heryan d the entrapped steam and water significantly reduce brakin.q and cornering c apabili - )- - ty. Th i s hy p othe s iswo u ld al so ex pl ain the d istinctive (s team c l eaned ) mark = left on the pavement in the tire path as shown in the aircraft ac c i d ent . ph o t o graphsin fig u re 8. Evidencefrom this aircraft wet runway skidding : . - accident as well as several others indicates that once started, reverted r u bb e r s ki dd ing results i n v e ry low tire / pavementfrictionwhich persists : down t o very l o w speeds . With tire op eration i n a n o nr o tatingmod e , th e l oss : o f tire corneringcapabilityfor directionalcontrol is possibly a greater " p r o bl e m,c ons i de ringr un way geometry, for pilots to overcome than the low _:. braking performance. Providing and maintaining runway surfaces with high 2 .
macrotexturean d go o d drainage characteristicsis very importantin allevl- ating the occurrence of this aircraft tire friction loss as well as those ; as so ciatedwith tire hydroplaning.
" Aircraft Landing Performance -" During aircraft ground operations , pilot techniquesand control inputs : toget h er with certain aircraft parametersincludingaerodynamics,engines, :. brake system, and landing gear configuration interact to determine how much ,y; , o f the a v ailabletire pavement traction is utilizedfor st o pping an d d irec- t i on al c on tro l purp ose s. T he inf l u e nc eo f spee d , tire tread condition,and _. pavement surface macrotexture on aircraft braking perf o rmance is illustrated i n figure 9 . These data wer e ob tai n e d du ring instru me nte d C V 9 90 aircraft .....
.. braki n g t e sts 8 condu c ted a t NASAWa l l o ps Fl ig ht C e nte r o wl a un i que resear ch : runway which features a variety of pavementsselected to providea wi d e range ; of surface macrotextures. A portion of each of these different pavementt; : _ " wa s mo d ified with instal l ation o f 6 x 6 x 2 5 mm ( 0. 25 x 0 . 2 5 x l-in. pitch ) . transversegrooves. For dry concrete conditions,the measured aircraft .7 _i_''; . ...... . . ..i' .. L L _' L _ . . . ,_.__: ...... L L L: ,_ L ___ i _ " _ i , - ":- , O RIGINAL PAGE IS ,: JOiE II N XI R QUALITY 10 ,_ ..
: . effect i ve bra k ing fr lr - t i o n cneffi ci ent ] _.w l indicated I n f i g u re 9 d ld no t " v ar y 51!]n l fl c lnt l y with tire tread de_l q n ar s u rfa c e co nfl q uratlonb ut _ome - decreasewan obs e r v e d with increa r .lng sp e ed. Th e o i ' fect o f spe ed waF , i_ u ch '_ _re pr o n o un c e d on the w,_t ungraa v ed surface, and these data in d ieat o t l lat -. .-- - -_4_ra , _u_4_I L 4zlco_vJ.de_d_a_Ll.gJEIJ_tJ__!Q.t__I j npr_vem_nt c o mp a rp.d w i th th,._ s_oth tire d ata. The calculated hy d roplaninq spin- do wn spee d o f 114 k nots .
i" n o te d in figure 9 is base d o n a tire inflationpressureof 1103 kPa (160 Ib l in 2) - On the slmilarlyw e tte d g ro ov ed concrete,the transverserunway grooves pro- _- d u ce d su b s ta n tia ll y greater aircraft bra k ing frictio n l e v e l s with b o th tire - treads than were shown by the wet ung_ - ooved surface data. These aircraft 2 br ak ing perf o rmanced a ta o n w et r unw ay s als o s u g ges t t hat t he e ffects o f t_,r e - tread wear are sec o n d ary t o t he effects of surface 9 re e ving b_cause o f the : . greatly enhanced tire / pavement water drainage capabilit y avai l able o n g r oove d i runways.
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" Anti skid Behavior The brake system is the primarymeans for stopping the aircraft. The d ev elo pmentand u s e o f a n tis k id c ont r ol system sdes ig n e d t o minimize ,; .- tire skidding and preventwheel lockupsduring braking has substantially : e n ha n c ed aircraft bra k ing p e rformancean d st opp ing capability. H o s t antiskid : s y s t e ms e m plo y t ou ch dow nand l ocke d -wheel p r o tectionf e atures in the brake .!"
• " . . c o ntr o l l og ic circuits t o p re v ent bra k e pressureapplicationto a nonrotating wh ee l as at t o uch do wn o e a s the re sul t o f l o w tire / pavementfriction conditions causing whee l lockup. The proper p e rf o rmance of these sy: ; tems, ho w ever, r p, .. .' . _ . d ep e nds o n a c c u rate i npu t s o f aircraft groun d speed and i_stantaneousbraked wheel angular velocity d ata coupled with efficient mechan i sms for reducing - an d rea p F, lylng hydraulicpress u re to each wheel brake unit. Effective " antiskid brake c o ntrol operation a l so re q uires posi t ive wl_eel spin-up T -' m ..........
• _ , II z _Z i . C acce ] eratlo n _after tire t o uchdow n a nd f o]] owi nq bra k e press u re re l ease du r_ : inq anti,kid cy_-llnq. S in ce whe_ l _pln-up charact_r'l, ; t | c ,; are d lr_ , ctl y i n _ : fl m_nced hy th e friction !.)anerated b(_l:_,_en th e tlr_ amidthe ru n w_ . J.r_k t ) contro l behavior can be sl o nlilcantlycompromiseddurinq aircraft operatlo n _ '" i - u n d e r adverse weather conditio n sand at high g round speed._ T i me precisionof , t . ' - - - , m i ' brake d wheel control by the anti._ki d deterioi'ates when low tire t ractio n - causes low whee l spln-up accelerations. Certain pilot inputs, such as full "' br a ke app licatio n b e fore t he whe e l s r e ach s y n chron ous aircraft s p ee d , can _: also adversely affect brake control because the logic circuits do not ': receive t_he correctaircraft ground speed referencevalue.
Aircraft Test Results _ . : . An example of such anomalousantlskid brake control operationfollowing touchdownis given in figure 10. These time history data collectedduring : wet runway tests with a large jet transportaircraft 32 illustratethe anti- skid brake control responseof the inboardwheels on a four-wheelbogie main landinggear to brake applicationsthat occurred prior to and after full wheel spin-up during landings. For brake applicationprior to full wheel spin-up, it is apparent from figure 10 that the ground speed referenceassumed by the skid-controllogic circuitfor the front wheel is wcll below the ._ actual aircraft speed. The low wheel spin-upaccel_rat l onsfollowingbrake pressure release during each braking cycle, combinedwith the low ground speed reference,preventedthe front wheel from attainingsynchronousaircraft speed until approximately30 secondsinto the lan d ing rollout. By that time, the aircraft speed had decreasedsufficientlyto cause high wheel spin-up _. accelerationand the proper ground speed referencesignal was acquired.
Subsequently, brP, ked wheel n M)tion was satisfactorily control l eddown to the J aircraft stop _oint. The much faster recoveryof aircraft synchronousspeed 1 "r i'- ' i f :. ORIGI NAL PA CT _ _ '- OF pOOR Q I l !q._:_ " ] 2 --. b y the mar tanfl_m whp.e l (_i q urn ] . ( ) ) r c :f l n_ : t, _ t h ( _ b,,ni_fit _ )I " path clear J n.q -. b y thn front ta i _dp, m whet_.l w l 1 1( : h l)_'odu (: , ,_, a l_r;s _,'l'ipp_r y r.L, rfac ( , f () r t he l : r a I I ir l!t w h ( _e l .
." . .................... _. ].qL Ir_ l( ) i_ ] :_ ( J Jn c l u d _ w h_ c , l an! -It _ l a r v , o'l _H:ity dia L _l ( _b t a l n_.d d uri n fl a : '_e c ond aircraf t lan d i w ! in whIcI_ br_;_kef ; w(; r( ; ap l) lied al'ter the Nlh e _els % re a ched Fu ll spin -up. Th_se braF,{,.d w h_.el responses su g gest that the pi l ot i : ' shoul d delay brake applicationduring landings on w et run w ays to allo w the ,, skid-controll og ic system sufficienttime to acquire an accurate ground speed reference. The considerablyreduced tire skidding experiencedduring : - this landing c o mpared to the data collected w hen brakes w ere applied _arly • : _ . suggests improvedaircraft stopping performanceand reduced tire wear.
• shou l d be noted that a comparisonof the braking effect _, ,;. emons_ated ._ by t h e two landings is not justifiedbecause the t_.;_ w ere , n ade at dif f ere r v _ • "_ aircraft gross weights and brake applicationspeeds.
. Comparativeaircraft braking effectivenessdata is presented in figure ; 1 1 for three landi p g tests conducted w ith a B- 7 27 aircraft equipped with an ,: . 22 " antiskid brake system. These test results, which show the varia t ionin _- effectivebraking friction coefficientwith speed for one dry and two wet ' runway landing cases, illustratethe significanteffect that tire / runway C . friction "andbra t (ed wheel control have on aircraft braking performance. For " the dry and wet runway landings (cases I and 2) conductedwith sufficient .
tire / runwayfriction to permit braked wheel control w ithout locking the wheel ; : a c o ntinuous increasein frictionwas measured as the aircraft speed decreased.
: As expected,significantlyhigher aircraft braking effectiveness w as obtained ; during the dry runway landing compared to the w et runway landing. The . . second w et run w ay landing, c a se 3, w _s made w ith an average surface w ater i :. depth abo_t twice that measured for case 2 . This great ( ,r runway wa t er depth !
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' _ Y_ ( ¢ J i_ 4 IV ' 13 : res u lte d i n mu c h lo w e r tir e / r u nwayfricti on an d a1 1 f ou r main gea r wh ee l s t l o ckedf ol low!ngbrake applicati o n. The s ubseq u entski dd ing pr od uce d a revertedrubber patch o n the tire such a s sh o wn in the ph o t o graphin figure : 11. With the devel o pme n t o f reverte d rubber ski dd ing,the aircraft braking eff e ctiveness wa s subs ta n tia l lyr edu ce d with little change in friction :- - . t h r oug h ou tth e lan d i n g speed ra nge. T h e c al cu lat ed aircraft s t opp i ng d i s tan ce • " f o r ca s e 3 i s a n proximatelytwice that f o un d f o r ca s e 2 . Of e qu al c o ncern, a l ocked (n on r o tating) w hee l ca nno t p ro v i de st abi l izingf o rces necessary for directi o nalc o ntrol. Anal o g o us l o w tire fricti o n re s ults were al so o btaine d during Langley track tests 6 when pr o longe d tire ski d ding on a wet s u rface ; p r oduced r eve rte d r ub b e r i n t he tire c o n ta c t p at c h.
Ad d itionalinsight i n to the lack o f directi o nalc o ntr o l a s well a s reverted rubber ski dd ing cau s e d by nonr o tatingtires was o btaine d d uring a recent investigation of a T- 3 8 aircraft lan d in g veeroff acci d ent which occurred at night during a moderate rainst o rm. A left-to-rightcr o sswind comp o nentcaused the pilot t o land the aircraft at a crab angle s lightlyright of runway center l ine. The acci d ent aircraft lan d ing run o ut track, i d entified by white mark s vi s ible o n the runway surface, is shown i n figure 1 2 t o gether with photographsof the ungro o ved,low texture d (clas s V), c o ncrete runway surface, the main landing gear (MLG) tire ski d patche s , an d the d amage d aircraft.
F o rtu n atel y ,t he p il o t escape d injury even though the nose and right main lan d inggear failed and the right wing tip was sheare d off s ub s equentt o the aircraft l e a v ingthe right shoulder of the runway, traversinga relatively . : so ft so il s u rface, a nd c om i ng t o r es t on a n i n tersecting p av ed taxiway. D u r- .... _ng the investigation which foll o we d the accident, the estimatedaircraft : t o uch d own po i n t n e ar th e r u nway int e r sec L_,_ was f ou n d t o b e a wat e r po nd in g area with water depths measure d up to 13 mm _0.5 in.). Additienalevi d ence I N ORIGINAL I _A C ';: I!, : , 1 4 : J_ OF . P OOR QU A Li fY - an d factorswh i ch ten d t o suppo rt the bel i ef that p o ssiblythe MLG tire s d i d .: . n o t spin up foll o wi n gt o uch do wn incl u d e the fa c t that tile aircraft t o uchdown " speed was significantly higher than the calculated tire hydroplaning spin-up '." s peed o f 119 kn o t s , the s urf a c e whit e marks from the MLG tires commenced - when the aircraft exited the deeply flooded portion of the runway and con- , _ . J _.. tinued to the runway shoulder edge, and only one skid patch, showing evidence , 2_..... of tread rubber reversion in the aft portion, was found on each MLGtire.
: Knowingthat he was landingon a wet runway, the pilot did not apply wheel - -' braking during "the aircraft runout on the paved runway and yet, reverted "i': rubber skidding evidentlyoccurred. Inspectionof the aircraft wheel brake assembliesrevealed no abnormalitiesand no indicationof dragging brake X .
. _ operation. In all other documentedaircraft accident / incident cases involving reverted rubber skidding, the pilot had employed wheel braking during the .; aircraft runout which contributedto locked wheel operation.
-.
.; - . Concl udi ng Remarks ": The principalweather, aircraft,runway, and pilot factors which combine to affect aircraft ground handlingperformanceduring wet runway operations ., - have been reviewed. This review included: identifying a relationship estab- • lished between rainfall rate and runway water depth; defining the major forms of tire friction losses; classifying pavement surfaces by macrotexture depth "_. and hydroplaningpotential;and evaluatingantiskid brake system performance.
• Research results from studies conducted at tile Langley Aircraft Landing Loads _" and Traction Facility,testswith instrumented ground vehiclesand aircraft, .)
: and a recent aircraft wet runway accident investigation were presentedto -_ illustratethe effects of various parameterson aircraft brakingeffectiveness.
. j : " These findings underscorethe complexityand variabilitywhich characterizes (_F ; ' () ' JR _W J }J o _ { " 1 5 ai, . craft wet runway o peration s . Research efforts, h ow e ver, h a ve re ve al e d s everal pr o misingmeans, such as the use of runway gr o oving and frequent rubber rem o val treatments, which offer improved tire / runwaywater drainage capabilityan d hence, contributet o safer aircraft operations. In reviewing the factor s influencingaircraft wet runway performance,severa l appr o aches o r needs h a ve a lso b een r ecogn i zed t o a 1 1e viate t he seve rity o f t h e pr o blem inclu d ing : c o ntin u e dupd ati n g o f pil o t e d ucati o nan d training p r o ce- d ure s ; implementati on o f p r o ce du re s f o r moni to ring s 11p p ery r u nway c o n d iti ons and identifyingseverity t o the pil o t ; improvementin anti s kid brake s y s tem perf o rmance;and prompt reme d ial treatment o f runway su rface d raina g e pr o blem s .
Reference s 1. H o r n e, Walter B.; and Leland, T raff o rd J. W. : Influence o f Tire Trea d Patternand Runway SurfaceC o n d iti o n o n Braking Fricti o n an d R o lling Resi s tanceof a M o dern Aircraft Tire. NASA TN D-1 37 6 , 1 962 .
2. Horne, Walter B. ; and Dreher, R o bert C.: Phen o mena o f P neumaticTire Hydr o planing. NASA TN D-2056, 19 63 .
3. J o yner, Up s hur T.; H o rne, Walter B.; and Lelan d , Traff o r d J. W.: In- vestigations o n the Groun d Perf o rmanceof Aircraft Relatlng t o Wet Runway Braki n gan d Slush Drag. AGARD Rept. 4 2 9, Jan. 196 3 .
4. Lelan d , Traff o rd J. W.; an d Taylor, Glenn R. : An Inve s tigati o n o f the Influenceof Aircraft Tire-TreadWear on Wet-RunwayBraki n g. NASA T N D - 2 7 )_ , April 1965.
'_ 5. Ho r n e, Walter B.: Skidding Accidentson Runways and Highways Can Be Re d uce d . Astr o nauticsand Aeronautics,vol. 5, no. 8, Aug. 196 7 , ; v pp. 48-55.
6, Horne, Walter B. ; Yager, Th o mas J.; an d Taylor,Glenn R. : Review of Causes an d Alleviationof Low Tire Tractionon Wet Runways. NASA TN b-4406 , 1968.
: ' :.., :; :.. . ;:iii • :i . : _ , : ' i _ . . : - : / . - _i_'ii' ii ::/ . . . _ • .
q ,. , = .
2 _ 7 . L e land, T raff o r d d. W . ; Y ag e r, T h o mas d.; and d o yn e r, Ups h u r T : Eff e ct s "" of Pavement Texture on Wet-Runway Braking Performance. NASATN D-43P.3, .. Ja nu ary 1 968 .
_ ' 8. Anon .: P a v eme n tGr oov ing an d Traction Studies. NASA SP-5073, 1969.
•_" 9. Yager, Thomas J.; Phillips, W. Pelham; _rne, Walter B.; and Sparks, - Howard C. (Aeronautical Systems Div., WPAFB): A Comparisonof Aircraft . : ; and Ground Vehicle Stopping Performance on Dry, Wet, Flooded, Slush-, : a nd Ice-CoveredRu n ways. NASA T N D- 6 098, N ov . 1970.
: ;' 10. Galloway,R. M.; Schiller,R. E., Jr.; and Rose, Jerry G.: The Effect L o f Rainfall Intensity,Pavement Cross Slope, SurfaceTexture, and Drainage Path Length on Pavement Water P-,e_,_.hs. _lexas Transportation • " Institutes, T exas A&M Uni v ersity,Research Report No. 1 3 8-5. Vehicle Pavement Interaction Research Study No. 2-8-69-138, May 1971.
" II. Ya g er, Th o mas d.: P r o gress in Airport Pavement Slipperiness Control.
- . Air Line Pilots Association18th Air Safety Forum, Dallas,TX, July . 2 0 -22, 19 7 1.
_! 12. Horne, Walter B.: Wet Runways. NASA TM X-72650, April 1975.
- 1 3 . H o r ne , Walter B.: Status of Runway SlipperinessResearch. NASA SP-416, _ October 1976, pp. 191-245.
: 14. H orne, Wa l ter B.; McCarty, John L.; and Tanner, John A.: Some Effects , , P o f A dve r se W e ather C o n d itionson Performanceof Airplane Antiskid Braking : Systems. NASA TN D-8202, July 1976.
15. Merritt, Leslie R.: Impact of Runway Traction on PossibleApproachesto - Certificationa n d Operationof Jet TransportAircraft. Paper 740497, S o c . Aut o m o tive Engineers, April-May, 1974. ,M i B
, .OF' Poo r Q u q L r ¢ 1 7
} 16. Ho r ne , Wal te r B .; a n d J o y ne r, Ups h u r T.: Det e rmi n i ng Ca us ati ono f Air c raf t ; . S k idd i ngAcci de nt so r Incid e nts. P a pe r p r ese nt ed at the 23 rd A n n u a l .... In te rnati o na l Air Safety Seminar, Flight Safety F o undati o n, Inc.
" ; (Wa sh in g t o n, DC) , Oc tobe r 1 9 70 .
1 7 . H o r ne , Walter B. : E l e ment s Affecting Runway Traction. (Preprint) 7 4 0 4 96 , Soc. A u t o m o tive Eng i nee r s , Ap rl1-May, i974.
18. Lan d er, F. T. W.; a n d Williams, T.: Th e Skid d ing Resistance o f Wet _ Ru nway Su rfa ces with R e f e r ence t o S u rface Te xture an d T yre Con d iti o n s .
: RRL R ep . LR 184, R o a d R es. L ab., B ritish Mi n istry o f T ra nspo rtation,1 968 .
19. Smiley, Robert F.; and H o rne, Waiter B.: Mechanical Pr o perties o f P neu matic T ir es With Special Referenceto Modern Aircraft Tires. NASA r- TR R-64, 1960. (Superse d es _CA TN 4110).
: 2 0 . Ho r ne , Walter B. ; a nd d o yner, U ps hur T .: Pneumatic T ire H yd r op la n ing _ an d S o m e Effect so n Veh ic le P e rf o rmance. SAE International Autom o tive : Engineering C o ngres s (Detr o it, Michigan), SAE 9 7 0C, Jan. 11-15, 1 9 6 5 .
,, ; 2 1 . Yager, T h o mas J . ; an d White, Ellis J.: Recent ProgressTowar d s Predicting ; Aircraft Gr o und Han d ling P e rf o rmance. NASA TM 81952, March 1981.
,a .
_ 22. Hor ne , Walter B.; Yager, Thomas J.; Sleeper, Robert K.; and M erritt, : L esl i e R . ( Fede ral Av iati on Ad minl s tration)_ Pr e liminary Tes t R esu lt s _:i o f th e J o int FAA-USA F -NASAR un way Research Pr o gram, Part I - T racti o n Measurements of Several Runway s Un d er Wet and Dry Con d iti o ns with a . ,_ Bo e i ng 7 2 7 , a D ia gon a l -Brake d Ve hi cl e, a nd a M u -Meter. NASA TM X - 73909 , •. , .
J ": " 1977 . 1 = ,. i ; !_ ........... .23 _ ._.Home Walt e ...... r _B.; Ya g er, Thomas d.; Sleeper, Robert K.; Smith, Eun t ce G o ; .? " : an d Merritt, Le s lie R. (FederalAviation Administration): Preliminary Tests Results of the Joint FAA-USAF-NASARunway Research Program, Part " II - Traction Measurementsof SeveralRunways Under Wet, Snow-C o vered, _:- and Dry Con d itionswith a Douglas DC-9, a Diagonal-Braked Vehicle, and
OnIGINA p Aa I S 1
. oF . pOOR QU A L I
T a M u- M e t e r . N A SAT M X-73910, 1977.
': 24. Stubbs, Sand y M.; a n d Tanne r , John A,: R ev i e w o f Anttsktd and B r ake D y n am ics Resea r ch. A i r c r a f t S af et y a nd Ope r ati ng P r oble m s, NASACP-2170, 1981, pp. 555-568.
2 5 . McC a rty, J ohn L . ; Y a ge r, T h o ma s J.; a nd R lccitiel lo ,S. R. : W e ar, : Fri c ti on ,and Te m p erat u reCharact e ri st ic s o f a n A ircraft T ir e Unde rg o i n g - Braking an d C o rnering. NASA TP 1 56 9, 19 79 .
• 26 . Y a ge r, T h o ma s J. ; a nd D r ehe r, R obe rt C .: T ra c ti on Ch aracteri s ti cso f a 30x11.5-14.5,Type VII, Aircraft Tire o n Dry, Wet, a nd Fl ood ed Surfaces.
: N ASA TM X- 7 2 805 , 1 976 .
2 7 . Tann e r, J o h n A. : R ev i e w o f NAS A Antiskid Braking Research. Paper 821 3 9 3 , Soc. AutomotiveEngineer s ,Oct. 198 2 .
: 2 8 . Y a ge r, T h o ma s J.; a nd B u hl man , F . : Macr o t ex tureand Drainage Measurements o n a Variety o f C on cr e te a n d A sp hal t Su rface s . AS T M S TP 763 , 1 982 , pp .
1 6 - 3 0.
2 9 . Lud ema, K. C.; and Gujrati, B. D.: An Analysis of the Literatureon T ire-Road S k i d R es i s tanc e . ASTM STP 541, 197 3 .
30. Henry, J. J.; an d Hegmon, R. R.: S u rfaceTexture Ver s u s Skid d ing: Measurements,FrictionalAspects, an d Safety Features o f Tire-Pavement Interacti o ns. ASTM STP 58 3 , 19 7 5, pp. 3 -1 7 .
3 1. Horne, Walter B.; an d Gri s w o l d , G uy D. (USA F , LangleyAFB): Evaluati o n o f High Pressure Water Blast with Rotating Spray Bar f o r Rem o ving Paint a nd R ub b e r D e p os its fr o m Airport Runways,and Review of Runway Slipperi- ness ProblemsCreate d by Rubber C o ntaminati o n. NASA TM X- 7 2 7 97 , N ove m be r 19 7 5 .
_ 32. Model L-I011 (BaseAircraft) Lan d ing PerformanceReport for FAA Evaluation : - of Concorde SST Specia l Condition25-4 3 -EU-12. Rep. N o . LR 2626 7 LockheedAircraft Corp., Jan. 14, 1974.
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