Not sure, but to my knowledge they arrest first and would check on those sorts of details later.<p>And yes, there is a "provision" for carrying a weapon through those cities, the Firearms Owners Protection Act (FOPA) of 1986, but it only provides a defense once you've been charged.  You would spend weeks or months with your life in turmoil, perhaps locked up (you're obviously a flight risk, no ties to the community) and spending significant money for competent counsel to get the charges eventually dismissed.<p>And this does frequently happen (arrests at O'Hare, La Guardia (sp?), JFK and I think Newark), enough so that I don't see the ruse as being worth the risk.