There's no room for the scooter in the cabin of the aircraft. If you are planning to bring it with you you'll have to check it the same way you do with your luggage.

When you get to the airport ask your airline for "Wheelchair Assistance" (aka "Sky Cap" - you can do this in person or in most instances on the airline's website). When you arrive at the airport they will meet you with a wheelchair and escort the disabled person through the Security Checkpoint, to your departure gate and at boarding time to the door of the aircraft - most likely the disable person will board the aircraft before "general boarding" begins. If the disable party is able to walk from the door to their seat they will do that, if not, the Sky Cap will transfer him/her to a smaller/narrower wheelchair and take him/her to their seat. Once on board and the aircraft is in flight NO wheel chair service will be available.

Upon landing there will be a wheel chair and attendant waiting to assist the disabled person disembark - you'll simply reverse the process and be escorted to the baggage claim area where you can pick up your checked luggage and the scooter. FYI - if the disable person can walk to the door of the aircraft you can deplane in the normal manner and a Sky Cap will be waiting by the door with a wheel chair. If the disable person is unable to walk to the door he/she will have to wait until all other passengers disembark and the Sky Cap will bring the "smaller" wheelchair directly to the seat.

It's all pretty easy and airlines do it on a regular basis. Contact your airline for more specific information.

I meant to add, the process is essentially the same whether you are flying domestically or internationally and is pretty well standard throughout the industry. Thus no different between your home airport and when you get to or leave Paris.

Please pay special attention to something RoamsAround says - the person will not have any wheeled device/assistance while on board. That means unless they can walk to the bathroom unassisted, they will not be able to use the bathroom while on the plane.

Assuming this person will be bringing the scooter, please make sure you understand rules for transporting such a device as baggage, in particular what types of batteries are allowed and how they must be secured.

And when you get to Paris, it must be charged daily. Make sure you have proper adapters and possibly a transformer, depending on the nature of the batteries.

Service for disabled people at the de Gaulle airport is actually quite good. The airline will notify the airport office in charge of disabled-person travel that assistance is needed. You will get off the plane last and be taken out onto a people-mover that looks like something out of Star Wars: it has a cabin that rises from the ground to connect with the plane's door. The device goes back down near the airport gates, and someone will be waiting to transport the disabled person to the special waiting room.

Then an attendant will take the person to go through Immigration Control and finally the baggage and Customs area. If you are connecting to another flight, the attendant will take you to an area near the gate, leave, and then return when it's time to board.

I would not wait until getting to the airport before requesting wheelchair assistance. It needs to be prebooked and this can usually be added to your online booking. Although industry standard, there are various categories of wheelchair assistance and airports don't have lots of wheelchairs waiting around, they could be booked out to other flights.

Also since you mention that 2 airline seats may need to be purchased, this is not a booking process that can be managed online, so you need to call the airline.

I disagree with these comment >>>Once on board and the aircraft is in flight NO wheel chair service will be available.<<< AND this one >>>the person will not have any wheeled device/assistance while on board. That means unless they can walk to the bathroom unassisted, they will not be able to use the bathroom while on the plane.<<<

Some airlines do have onboard wheelchairs which is used to help passengers to the bathroom. The crew can wheel it but that's about it, the person must be able to get themselves in and out of the onboard wheelchair and in and out of the bathroom unassisted or if they cannot do this, they must travel with someone who can assist otherwise they could be refused boarding. Once again, prebooking is very important, you don't want to turn up at the airport asking for this service.

Odin - my patients with disabilities would greatly appreciate knowing which airlines ever have on-board wheelchairs since they have all reported to me not being able to fly or flying with great discomfort, fluid restriction, and sometimes requiring diapers or catheters because of lack of access to bathrooms on-board.

Here are a couple, I looked at AF since the OP question was about travelling to CDG from the US, although didn't say where in the US

http://www.airfrance.co.uk/GB/en/common/guidevoyageur/assistance/pmr_handicap_moteur.htm - scroll down to onboard wheelchair

http://www.united.com/web/en-US/content/travel/specialneeds/disabilities/cowheelchair.aspx?Mobile=1

http://www.virgin-atlantic.com/gb/en/travel-information/special-assistance/medical-facilities-onboard.html

http://www.aa.com/i18n/agency/Travel_Experience/Accept_pax_wheelchairs.jsp#In-Flight%20Wheelchairs

http://www.britishairways.com/travel/disabilityassistanceinfo/public/en_gb
Scroll down to Onboard section

I believe they have to be able to get themselves in and out of the lavatory though and in and out of the onboard wheelchair. I also don't agree that there is no difference between domestic and international, since there is a difference on aircraft type and flight time so not all aircraft might have an inflight wheelchair. Best to check your individual situation with the airline because it is up to them.

I feel for people with disabilities. It is hard enough to negotiate the toilets as an able bodied person.