The Washington, DC law doesn't apply to people passing through:
The exception here may be a bit squishy-sounding but if you're diverted to a DC airport you're either in Virginia (DCA and IAD) or Maryland (BWI), so the DC law wouldn't apply to you anyway.

The FOID law in Illinois has a big exception that applies to air travelers:
Another Google search reveals that flying into and out of Chicago airports with declared firearms in checked baggage is a non-issue.

I was imprecise earlier in that I didn't exclude international destinations; I meant only US airports.

Still, you have to wonder if that's really true when you read stories like this:

http://www.washingtonexaminer.com/warnin...article/2535216

I continue to believe that going anywhere near a firearm-hating state (district) with a firearm in your possession is just asking for trouble. That includes accidentally getting diverted there when you actually had zero intention of setting foot in the place.

What is that cop saying I've heard, "You can beat the rap, but you can't beat the ride". Something like that. Alluding to the situation where you may ultimately escape legal penalty, but only after enduring much inconvenience, wasted time, confiscated possessions, lost job, jail time, lost money for legal representation, etc.

This thread has diverged from the initial question regarding knives to firearms. But I think the discussion is still very relevant. Often times, once a place goes after guns hog wild, and finds that in the end that doesn't really help anything, then they go after knives. A fantastic example of this is Great Britain, with their current "knife crime" hand wringing. They pretty much totally outlawed guns. And then didn't they move on to knives? They were trying to outlaw pointy knives. I don't know if that effort succeeded. I think they have outlawed locking knives, haven't they? So it's not a good idea to overlook what a place does against firearms owners thinking "they'll never do that to my knives". I think someone thinking like that would be in for a rude surprise. I also have a hunch that someone who looks at a knife foremost as a tool, but something that someone of evil intent can use as a weapon, probably looks at firearms the same way. Similarly, someone who has an irrational fear of guns probably has an irrational fear of knives too. And the irrational folks are the ones pushing these crazy restrictive laws. So firearms and knives are closely related when it comes to "rights".

There hasn't been any recent change in knife laws here. Pen-knifes are presumed tools, and other knifes are presumed weapons, but both presumptions are rebutable. So it's not so much that they are outlawed, as that carrying a knife that isn't a pen-knife needs a specific justification. A vague, "I might need to cut something" isn't specific enough. The hand-wringing is mostly directed at gangs, mostly teenagers, who use knives as weapons to cause lasting bodily harm. Knife-crime is a real issue here.

I actually think our statute law is reasonable, as it does acknowledge that pen-knives are tools that need no further justification to carry. The problem is that the statute did not consider locking blades at all, and some case law has established precedent that locking blades are classed with fixed blades. The way those cases arose meant that the argument that a lock is a safety feature never really got made. So the case law is bad, but unlikely now to get over-turned.