Hello,
@Smd1305, and welcome to Talking Point. I am sorry you have needed to find your way here but hope it will be helpful for you.
If you can be patient with me, I will post some links that might be useful. This is a topic that comes up from time to time on Talking Point. It's not an easy answer, as everyone is an individual and what you are able to manage, will vary widely.
My mother, now in a care home and either in later middle stages or earlier later stages of Alzheimer's, has not been capable of any sort of real travel for at least seven years; short car journeys are now all she can manage and those only when necessary for doctors' appointments. She doesn't mind riding in the car but getting her in and out can be difficult. She is physically quite well, apart from some arthritis, but her visual impairments (both from physical problems and the dementia), inability to process verbal directions at times, and so on, can be challenging. She also gets easily confused and overwhelmed in situations such as a busy doctor's surgery. She has no patience and cannot wait easily for an appointment. She goes to the toilet frequently, and is also sometimes incontinent, so that entails taking a lot of supplies and spending a lot of time in the toilet and feeling nervous about accidents. These appointments tire her a great deal and that can make her irritable and angry and aggressive. You get the idea.
I would urge you to think the situation through carefully, whatever you do. I wouldn't attempt a long haul flight with a person with dementia, even in early stages, but others would and have. As above, I'll post some links for you in a moment.
If you are comfortable telling us more about the situation we might be able to offer more specific advice, but no pressure.
I am off to find some info for you. Best wishes.