Not only does CO have the form on the website, they'll point you towards it when calling -for instance to get seatassignment done for those seats that can not be assigned online-.
Cheshire Figment; my experience is that 3 pages is way to much. Those handling the chair tend to scan info put onto an aid, which will decrease the likelyhood of them actually paying attention to 3 pages. One page or a 'fixed frame' like CO has been offering since very recently gets the best shot of drawing the proper attention.
K; depening on the airline, you CAN find the info regarding dimensions. For instance, I know CO has them online. Airlines that don't have them online have been known for giving that info when calling them and asking for it. This can be done BEFORE booking, so you can make decisions based on that info. It isn't just about dimensions, though. It varies per type of aircraft how they'll have to load the chair. Eventhough the loading dimensions might be the same, it can be that in type A they can load the chair in a different container from other luggage and in type B they;ll have to combine suitcases and chair into one container.
While proper loading should avoid this being a major difference, having a chair in the same compartment/container as other luggage is slightly increasing the risk of damage. This is the exact reason CO might decide to change my flights for my sept/oct trip to WDW. I could only book certain flights -some other options CO offers were way to expensive- and did so with full confidence, I might add. Because I had some minor problems on a previous CO flight, a CO concierge at my home airport is working very closely with me to make future trips perfect. She noticed that for one of the flights I'm booked on, the chair would not be loading seperately, thus a slight increase of risk. It's not sure yet this type of aircraft will carry out that flight since it's a recent switch of material and time will tell if they keep with it or chance it back. If they do keep with it, chances are that CO will rebook me onto a different flight, purely because of the chair.
I would always disconnect the power, preferrably to such an extend 'outsiders' can not turn it back on without you being there. It's unforgivable, but you'ld be surprised how many folks will go joyriding if they get the chance. And not all of them are skilled enough to start with. A lot of chairs will come with this feature as a basic.
What I always do is having a 'back up plan'. (Long) before I fly anywhere I think about what could go wrong and how could I deal with that? Having a back up strategy has a couple of nice sides.
1) I don't stress about 'what if's', as I know I'm prepaired
2) If problems do occur, I know what to do.
For the 'back up' I always make sure I know which dealers have knowledge about my type of chair and features around the area I'm flying to. With a new chair or new feature, I talk to my dealer at home to find out what they can do for me if something does happen. What can I do myself? I add insurance for the chairs (flying internationally, they only cover damage according to the Warschau convention which in no way covers even a manual chair, let alone a powerchair) and go on my merry way.
When taking proper precautions, flying tends to be pretty relaxing and goes off without a hitch more often than problems. I'm lucky and unlucky that my chair has a certain feature on it that is very proun to damage. It can not be removed and protective wrapping will only do so much. It's had it's share of damage, for sure.

Combine that with a home airport that cares squat about proper wheelchair handling and you've got an interesting combination.

And even I don't have a 100% score with things going wrong beyond needing to fix a screw or something.
