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acentralfactortoaviationmeteorologyandthesafetyofaerospacenavigation.
Evenaslightdewpointdeficitisthecauseofonethemostdangerous
phenomenainaerospacenavigation-icing,i.e.theprocessoficedeposition
onthesurfaceofaircraftorspacecraft.Themechanismresponsibleforthe
formationoficecoatingonthesurfaceoffyingobjectsisdesublimation,i.e.
thedirecttransitionofwatervapourintoafrozenstateonthesurfaceofthe
objectinquestion.
Inaerospacenavigation,itisthereferenceatmosphere,alsoknownasthe
InternationalStandardAtmosphere(ISA),acceptedandadoptedafterWorld
WarIIbytheInternationalCivilAviationOrganisation(ICAO5),whichprovides
themostaccuratepointofreferenceregardingatmosphericconditions,
measuredfromtheEarth)ssurfacetotheheightof30km.Inthisrange,the
aircompositionatthegroundlevelandthemeteorologicalelementsatsea
levelareconsideredtobeconstant.Theseparametersarecalculatedunder
theassumptionthattheatmosphereisastaticsystem,theairisadrygasand
itschemicalcompositionisindependentofheight.
Thepurposeofestablishingthereferenceatmosphereistospecify
conditionsforthecomparisonoftheperformanceoffyingobjects,aswell
asforstandardisationpurposesinmodellinganddesignofaircraftand
spacecraft.Thereferenceatmospherevaluesalsoprovidethebasisforengine
performancespecificationaswellasconstitutethepointofreferencefor
determiningthegraduationofon-boardinstrumentationanddevices,finally,
theyenablestandardisinggeophysicalandmeteorologicalobservations.
Table1belowshowsstandardatmosphericparametersaccordingtoISA,
i.e.pressure,temperature,density.
Table1.Basicparametersofthestandardatmosphere(Curtisandothers2009,pp.18-19)
Pressure
Density
Temperature
Humidity
Parameter
Value(baseunits)
1.2255kg/m3
1013.25hPa
15.150C
0%
760mmHg;29.92inHg
Value(otherunits)
288K
5
InternationalCivilAviationOrganisation–ICAOhasbeenestablishedasaresultofthe
ChicagoConvention,whichenteredintoforceon4April1947.ICAOisaglobalorganisation
whoseactivityfocusesonthepreparationandaffirmationoflaws,rulesandprinciples
essentialtoairtrafficsafety.TheseregulationsareattachedtotheChicagoConvention
asICAOannexes,approvedbytheICAOCouncil.Theyadoptthetypeofstandardsor
recommendedprinciplesofoperation.Asofnow,19ICAOPannexeshavebeendeveloped.
Theyregulateairnavigationwithregardstoe.g.PersonnelLicensing,OperationofAircraft
andEnvironmentalProtection.
19
