AnaccidentthatoccurredintheskiesovertheGrandCanyonin1956resultedintheestablishmentoftheFederalAviationAdministration(FAA)toregulateandoverseetheoperationofaircraftintheskiesovertheUnitedStates,whichwerebecomingquitecongested.TheresultingstructureofairtrafficcontrolhasgreatlyincreasedthesafetyofflightintheUnitedStates,andsimilarairtrafficcontrolproceduresarealsoinplaceovermuchoftherestoftheworld.Rudimentaryairtrafficcontrol(ATC)existedwellbeforetheGrandCanyondisaster.Asearlyasthe1920s,theearliestairtrafficcontrollersmanuallyguidedaircraftinthevicinityoftheairports,usinglightsandflags,whilebeaconsandflashinglightswereplacedalongcross-countryroutestoestablishtheearliestairways.However,thispurelyvisualsystemwasuselessinbadweather,and,bythe1930s,radiocommunicationwascomingintouseforATC.Thefirstregiontohavesomethingapproximatingtoday'sATCwasNewYorkCity,withothermajormetropolitanareasfollowingsoonafter.Inthe1940s,ATCcentrescouldanddidtakeadvantageofthenewlydevelopedradarandimprovedradiocommunicationbroughtaboutbytheSecondWorldWar,butthesystemremainedrudimentary.ItwasonlyafterthecreationoftheFAAthatfull-scaleregulationofAmerica'sairspacetookplace,andthiswasfortuitous,fortheadventofthejetenginesuddenlyresultedinalargenumberofveryfastplanes,reducingpilots'marginoferrorandpracticallydemandingsomesetofrulestokeepeveryonewellseparatedandoperatingsafelyintheair.ManypeoplethinkthatATCconsistsofarowofcontrollerssittinginfrontoftheirradarscreensatthenation'sairports,tellingarrivinganddepartingtrafficwhattodo.Thisisaveryincompletepartofthepicture.TheFAArealisedthattheairspaceovertheUnitedStateswouldatanytimehavemanydifferentkindsofplanes,flyingformanydifferentpurposes,inavarietyofweatherconditions,andthesamekindofstructurewasneededtoaccommodateallofthem.Tomeetthischallenge,thefollowingelementswereputintoeffect.First,ATCextendsovervirtuallytheentireUnitedStates.Ingeneral,from365mabovethegroundandhigher,theentirecountryisblanketedbycontrolledairspace.Incertainareas,mainlynearairports,controlledairspaceextendsdownto215mabovetheground,and,intheimmediatevicinityofanairport,allthewaydowntothesurface.ControlledairspaceisthatairspaceinwhichFAAregulationsapply.Elsewhere,inuncontrolledairspace,pilotsareboundbyfewerregulations.Inthisway,therecreationalpilotwhosimplywishestogoflyingforawhilewithoutalltherestrictionsimposedbytheFAAhasonlytostayinuncontrolledairspace,below365m,whilethepilotwhodoeswanttheprotectionaffordedbyATCcaneasilyenterthecontrolledairspace.TheFAAthenrecognisedtwotypesofoperatingenvironments.Ingoodmeteorologicalconditions,flyingwouldbepermittedunderVisualFlightRules(VFR,视觉飞行规则),whichsuggestsastrongrelianceonvisualcuestomaintainanacceptablelevelofsafety.PoorvisibilitynecessitatedasetofInstrumentalFlightRules(IFR,仪表飞行规则),underwhichthepilotreliedonaltitudeandnavigationalinformationprovidedbytheplane'sinstrumentpaneltoflysafely.Onaclearday,apilotincontrolledairspacecanchooseaVFRorIFRflightplan,andtheFAAregulationsweredevisedinawaywhichaccommodatesbothVFRandIFRoperationsinthesameairspace.However,apilotcanonlychoosetoflyIFRiftheypossessaninstrumentratingwhichisaboveandbeyondthebasicpilot'slicensethatmustalsobeheld.onaltitudeandnavigationalinformationprovidedbytheplane'sinstrumentpaneltoflysafely.Onaclearday,apilotincontrolledairspacecanchooseaVFRorIFRflightplan,andtheFAAregulationsweredevisedinawaywhichaccommodatesbothVFRandIFRoperationsinthesameairspace.However,apilotcanonlychoosetoflyIFRiftheypossessaninstrumentratingwhichisaboveandbeyondthebasicpilot'slicensethatmustalsobeheld.Controlledairspaceisdividedintoseveraldifferenttypes,designatedbylettersofthealphabet.UncontrolledairspaceisdesignatedClassF,whilecontrolledairspacebelow5,490mabovesealevelandnotinthevicinityofanairportisClassE.Allairspaceabove5,490misdesignatedClassA.ThereasonforthedivisionofClassEandClassAairspacestemsfromthetypeofplanesoperatinginthem.Generally,ClassEairspaceiswhereonefindsgeneralaviationaircraft(fewofwhichcanclimbabove5,490manyway),andcommercialturbopropaircraft.Above5,490mistherealmoftheheavyjets,sincejetenginesoperatemoreefficientlyathigheraltitudes.ThedifferencebetweenClassEandAairspaceisthatinClassA,alloperationsareIFR,andpilotsmustbeinstrument-rated,thatis,skilledandlicensedinaircraftinstrumentation.ThisisbecauseATCcontroloftheentirespaceisessential.Threeothertypesofairspace,ClassesD,CandB,governthevicinityofairports.Thesecorrespondroughlytosmallmunicipal,medium-sizedmetropolitanandmajormetropolitanairportsrespectively,andencompassanincreasinglyrigoroussetofregulations.Forexample,allaVFRpilothastodotoenterClassCairspaceisestablishtwo-wayradiocontactwithATC.NoexplicitpermissionfromATCtoenterisneeded,althoughthepilotmustcontinuetoobeyallregulationsgoverningVFRflight.ToenterClassBairspace,suchasonapproachtoamajormetropolitanairport,anexplicitATCclearance(飞机起降的许可)isrequired.Theprivatepilotwhocruiseswithoutpermissionintothisairspaceriskslosingtheirlicense.19.SomeimprovementsweremadeinradiocommunicationduringWorldWarⅡ.
19.有程序如下：#include"stdio.h"intmain(){inti,j,k,temp;int*p1,*p2;scanf("%d%d%d",&i,&j,&k);p1=&i,p2=&k;temp=*p1;*p1=*p2;*p2=temp;printf("%d,%d,%d\n",i,j,k);return0;}执行该程序，输入数据7119【Enter】，则程序输出结果为
19.有程序如下：#include"stdio.h"intmain(){inti,j,k,temp;int*p1,*p2;scanf("%d%d%d",&i,&j,&k);p1=&i,p2=&k;temp=*p1;*p1=*p2;*p2=temp;printf("%d,%d,%d\n",i,j,k);return0;}执行该程序，输入数据7119【Enter】，则程序输出结果为