A couple comments:
Flight of Passage in Avatar:
We have gone to this with our daughter multiple times and she has stayed in her manual wheelchair in both preshow rooms and into the ride car room. We have always been assigned numbers on the ends of rows, which allowed us to ‘overflow’ into the area of the floor without numbers. I have also been in those rooms with other guests using wheelchairs, including power wheelchairs. My DD’s wheelchair is fairly narrow (25 inches wide) but wider ones look like they would fit.
ECVs can’t turn very sharply, which is probably why they are not allowed in the preshow and boarding area. I don’t know why they would have turned down a power wheelchair to go all the way to loading; it’s possible it could have been a misunderstanding
Pirates of the Caribbean at WDW:
The ride loads in one building and unloads in another building, one floor down from where guests come in. CMs have to move mobility devices from the loading area into the unload area (using a small elevator). That’s the reason they prefer everyone to use an attraction wheelchair - there have been situations where the guest got to the unload area before their personal wheelchair.
After unloading, boats go into an area that’s just high enough for the boat itself to go thru in order to get back to the loading area. Because of this, they can’t have guests with mobility devices load and unload in the same location like some other attractions do.
The ‘alternate entrance’ requires a CM to bring the guest backstage near to the door used to bring mobility devices out of the load area. There may be a wait for a CM to be free; the advantage to the ride CMs is the CM can take the device right to the unload area after the guest gets off it.
Interesting fact: in the ‘way past’, people’s personal wheelchair were actually loaded onto the boat with them if the wheelchair was small/light enough and could be folded. The guests got into the boat and the CM basically ‘tossed’ the wheelchair into the back row. I’ve heard 3 reasons they stopped down that; CM back injuries getting wheelchairs on and off, wheelchairs getting damage during the ‘toss’, wheelchair falling off of the boat during the fall
Buzz Lightyear at WDW:
The alternate entrance is at the exit, which is a tight and congested area.
The ride exits into a gift shop into the area where guests getting off the ride congregate to look at their on ride photos. So, to get there, you would need to navigate ‘against the flow’ in the gift shop and photo viewing area. The actual exit is a pretty small area and has only a small area where wheelchairs or ECVs can park. We use the wheelchair car for our daughter and when getting out, CMs have often needed to move a mobility device so we can exit.
These screenshots from a
YouTube video show how tight the area is. Blue arrows show where mobility devices are sometimes parked.

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