I've done it. I hate it.
I wouldnt travel with my Cirrus unless it was boxed up in the hard case.
My old Ibanez... different story.
+1
I must admit I have written most of this before, but I seem never to tire of telling people about it because I am so disappointed in TSA and the airline industry's treatment of musicians.
You must have the best instrument insurance you can find!!!
I have a very tough heavy-duty all recessed hardware "100% ATA compliant bass case" (Recessed Latches, Ball Corners, Recessed Handle, 1/4" ABS sides). It weights about 35 lbs. Inside is form fit foam for my bass. The case is lockable, but the locks are not TSA locks, the kind that TSA can unlock with their "master key." BTW, if you think crooks are going to be bothered by any lock, you are wrong. Case locks keep honest people honest. Crooks break them, or smarter yet, take the whole thing, case and all.
I painted it Olive Drab to make it a little more unique, and who knows--maybe look a little less like a bass case to the eyes of thieves.
I have used it many many times, and found that the TSA loaths it. They always warn me that it will have to be hand inspected, and because they are so busy, may miss my flight. I learned quickly and after it was once delayed by 6 hours, I have always checked in over an hour before my flight when traveling with this heavy thing. Of course, while this improves the chances of it making my flight, it also increases the amount of time the bad guys have to snatch it.
Who are these bad guys? Airline employees, that's who. I know of a number of thefts of lugguage or contents of lugguage while the items were in the airlines possession. BTW, IMHO Europe is very bad for this. We have had our worst theft experiences in Germany with Lufthansa. There are crooks in all cultures and in all walks of life, sadly.
Back to TSA. I once flew to Portland, OR from Lexington, KY with a Lakland 55-01 Deluxe in my olive drab case. When I entered the airport, the person at the ticket counter informed me that firearms are not allowed in the airport, I just grinned and in my best faux kentucky gent ultra-slow drawl said, "Well now 'Mam, I know that. But ya'll see, this here is a Bass Geeetar." When I got to Portland and retrieved the bass, I opened the case to discover it was partially disassembled. TSA had removed the back panel, the knobs, input jack, and pots/pre harness.
It was easy to assemble because they hadn't lost any screws or parts, and no harm was done, but it gave me an idea of their attitude toward instruments. This was Delta, IIRC. I might add that on one trip to Hawaii, upon arrival I discovered my rental car was too small to fit the ATA road case and my wife and our lugguage, so I had to upgrade (the car that is).

These cases are wider than the back seat of the majority of automobiles. Make sure the back seat folds down.
So, I soon realized these were my choices:
0) Don't fly.
1) Don't fly with a bass.
2) Fly with a cheap bass in a gig bag, that has a 50/50 chance of going into the cargo hold at the gate (happens to me about half the time).
3) Fly with a cheap bass in a heavy big case, check it and leave the case unlocked on orders from TSA--and for the ease of airline thieves--check in way early, upgrade my rental, and lug it around between worrisome legs of travel, and reassemble as needed).
4) $hip it Fed-Ex. N.B., Fed-Ex put$ the declared value of the box content$ ON THE OUTSIDE OF THE BOX!!!!!!

5) rent a bass when I am going.
6) buy a ticket for my bass.
I have been using 4, but am considering 5 and 6.
IMHO, until deregualtion, flying was comfortable, fun, expensive, and romantic--a literal cocktail party in the air. The food was never great, but it was edible. The crew used to be twice as big, and tried very hard to solve any and all problems. The deregulation made all of that slowly turn into what we have today, most of which corporate greed had accoumplished before 911, IMHO.
Final word: If some one can steal your belongings after they are checked, why can't they put something INTO your luggage, too?