[sorcerer-mar]

You presumably know this but just to clarify for other readers: it's if you willingly give your data to a third party (the airlines) and the third party willingly gives it to the government, then it's not a violation for the government to use it.

Note there's an exception for cell tower data because courts ruled that cellphones are absolutely necessary for people to live their lives today. They collect so much data that applying Third Party Doctrine to that data is tantamount to a 24/7 100% carte blanche surveillance system across the entire country, so SCOTUS carved this one out.