One thing I've done in the past to try to prevent losing parts is everything that comes off the wheelchair other than the cushion, which I sit on during the flight, (foot plates, headrest, armrests, etc.) goes into a laundry or garbage bag and comes in the cabin with me. I can't get charged for extra baggage as long as everything in the bag is medical supplies and that way I know all the peripherals are with me and not going to get lost in the hold. Personally, I wouldn't want to try to put my entire chair in a bag, but I also have an adult-sized rigid chair. Also, if my chair is in a bag, the baggage crew can't roll it anywhere (which is substantially easier than carrying it).