Build a Flight Tracker

I need to add 2 or more airplaneEntity to the example.
How can I do it?

That is the link of the example:

You can use the snippet of code that adds the airplane in the flight tracker tutorial to add additional airplanes:

const airplaneEntity = viewer.entities.add({
       availability: new Cesium.TimeIntervalCollection([ new Cesium.TimeInterval({ start: start, stop: stop }) ]),
       position: positionProperty,
       // Attach the 3D model instead of the green point.
       model: { uri: airplaneUri }, // Add your own airplane url here 
       // Automatically compute the orientation from the position.
       orientation: new Cesium.VelocityOrientationProperty(positionProperty),    
       path: new Cesium.PathGraphics({ width: 3 })