I'd suggest looking at Admiral Cloudberg's recent analysis of the Jan. 2025 airliner/military helicopter collision in Washington DC. It's a study in the difficulties of air traffic control in the 21st century and the reality of transponder usage, complicated by an overwhelmed airport and legislative indifference. Transponders aren't universally used, technology and people aren't perfect.

This one is long; I suggest reading the first chapter, then skipping to chapter 7 for the important parts of the story.

https://medium.com/@admiralcloudberg/reaping-the-whirlwind-i...