Section 107

I am not disagreeing with you, just pointing out that each state has different definitions and requirements. Based on the definitions of the state, that "unless" is a really big caveat. In some jurisdictions, even though the conversation happens in public that does not mean one of the actual parties in the conversation does not have a reasonable expectation of privacy. Most states (Virginia) are "one-party consent" and others (CA) require "all-party" consent.

Cites for audio recording: It's been a while and what came first to mind were the eavesdropping laws of Illinois and Maryland where there were some notable cases of folks being charged with felonies for audio recording their arrests. But quick research shows federal appeals courts found those laws unconstitutional.

Those cases involved actual law enforcement; conversations of law enforcement is altogether another creature - generally their conversations in the performance of their official duties in a public place do not enjoy any expectation of privacy. But we know darn well on this forum that TSOs are not law enforcement (and that perhaps TSA needs to teach this fact to their employees more effectively) so perhaps TSO's conversations do enjoy a greater expectation of privacy? I suspect that courts will view TSOs as public employees performing their official duties in a public place and therefore will/would not grant them greater expectations of privacy than LEOs. But I don't know for sure.