The short answer is No. no one has a definitive answer. FAA rules in the U.S. state that Folder under 4" is legal, however, individual airlines, airports, and local jurisdictions are fee to make up more restrictive policies. Airport security officers who may or may not know the FAA rules, or any or all of the other rules are pretty much free to interpret any of the rules as they see fit, or to just make them up as they go.
Many here will tell you that serrated blades are out, although I have never had a problem within continental US with them.
Outside U.S. different laws apply. Mexico has in theory fairly restrictive laws, although I have heard people say that they have carried fairly large folders (AFCK) into, and out of Mexico with out problem.
You will reduce your chances of problems if you pack the knife in your checked luggage rather than carrying on your person.
Mike