var czml = [{
    "id" : "document",
    "name" : "CZML Model",
    "version" : "1.0"
}, {
    "id" : "aircraft model",
    "name" : "Cesium Air",
    "position" : {
        "cartographicDegrees" : [-77, 37, 10000]
    },
    "model": {
        "gltf" : "../../SampleData/models/CesiumAir/Cesium_Air.glb",
        "scale" : 2.0,
        "minimumPixelSize": 128
    }
}];


var updatedCzml = [{
    "id":"document",
    "name":"CZML Model",
    "version":"1.0"
},{
    "id":"aircraft model",
    "position": {
        "cartographicDegrees":
        [-139.23640674352512,24.89787519772953,48897.796695947756]
    }
}];



var czmlStream = new Cesium.CzmlDataSource();


var viewer = new Cesium.Viewer('cesiumContainer', {
        infoBox : false,
        selectionIndicator : false,
        shadows : true,
        automaticallyTrackDataSourceClocks : false
});

viewer.dataSources.add(czmlStream.load(czml));


Sandcastle.addToolbarButton('Process', function() {
    czmlStream.process(updatedCzml);


});

https://www.html5rocks.com/en/tutorials/eventsource/basics/#toc-security

https://www.howopensource.com/2014/12/introduction-to-server-sent-events/

Source – Hannah Pinkos