The data broadcast from ADS-B includes both GPS position (Lat + Lon) and altitude. If you created a bounding box, you could add a height parameter to make it 3D, and get a list of such aircraft and the timestamps of their transmissions while inside that (3D) bounding box.
That wouldn't be too difficult to do with a little bit of filtering of the feed coming out of an ADS-B receiver.
An RF receiver is not required for the subject use case, they can use existing ADS-B IP feeds, process the feed (either live or with historical data) according to the 3D bounding box, and generate reports based on flight paths intersecting the bounding box.
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Airloom – 3D Flight Tracker - https://news.ycombinator.com/item?id=46080289 - November 2025 (106 comments)