I have a recommendation for any UK-based Kronos owners: Castle Cases, based out of Tamworth, web site
http://flightcasefactory.co.uk.
I wasn't convinced by some of the generic keyboard cases I saw available on the web, so I asked these guys to build me a custom case for my Kronos 73. I live in Birmingham so I took my keyboard in to their workshop and they measured it up by hand. The resulting case (and my keyboard) are shown on the product page here:
http://www.flightcasefactory.co.uk/prod ... ts_id=1475
The case fits well and contains head-room and foam supports to prevent the joystick/screen touching anything. It cost about £150+VAT+postage, and weighs about 10kg. I don't know about flying, but it's easily strong enough for driving around in a van and storing the keyboard backstage at gigs.
I have a K73 so that's what's listed on their web site. If you have a K61 or a K88, you could call them up and ask if they can tweak the length of the case to fit.
I'm not affiliated with these guys in any way - I'm just really happy with the case I got. More than happy to post pictures if anyone wants more a detailed view.