The only reason commercial aircraft are not accessible is because airlines don’t want them to be.

As the petition points out, all the research and designs and safety checks into aircraft having accessible bathrooms and spaces for wheelchairs has been done. But airlines won’t implement them even though it is interesting to note that some airlines now have what are really first class individual cabins with showers etc -but apparently don’t have room for wheelchair spaces and other accessible features like accessible bathrooms! 
United Airlines can make its upcoming replacement fleet accessible if they choose to. They need to be encouraged to do so. You have already signed the petition calling on United to become accessible but could I ask you to encourage family members or friends to also sign the petition- https://www.change.org/p/accessible-air-travel-for-all

Thank You Again.

Pekka