The site https://www.adsbexchange.com/ offers tons of feeds with info about flights.
Example: https://samples.adsbexchange.com/traces/2021/08/01/22/trace_full_440122.json
Local stored JSON: https://api.json-content-importer.com/extra/json/adsbexchange-trace_full_394a0b.json
Out of such JSON-data with the flight route you can create other feeds, like a KML-Feed. See how this can be done:
Create a JCI-Template:
- URL: https://samples.adsbexchange.com/traces/2021/08/01/22/trace_full_440122.json
- Name: kmladsbexchange
- twig-template:
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
<Document>
{% for k,v in trace %}
<Placemark>
<name>
<![CDATA[
{{desc}}: {{r}}
]]></name>
<description>
<![CDATA[
Alt: {{v.8.alt_geom}}
]]></description>
<Point>
<coordinates>{{v.1}},{{v.2}}</coordinates>
</Point>
</Placemark>
{% endfor %}
</Document>
</kml>
In Action: https://api.json-content-importer.com/kmladsbexchange/?show=oc