In an ideal world, passengers will notify the airline of any medical conditions, but I know that this doesn't always happen. (I have been crew for years).

People with advanced Alzheimer's are no doubt already on medication. If airlines are informed, they may well ask the patient's doctor to supply a fitness to fly letter. I know that as crew, if we are at all concerned about a passenger on boarding, before take off, or indeed during flight, we can contact Medlink and they will assess fitness to fly. It has happened that we have had to refuse to carry a passenger, but it is rare. This was not a patient with Alzheimer's, I should add.

Alzheimer's is unpredictable, the individual can be calm and happy one moment, violent the next, so it isn't always apparent there is a problem.

As to the question about pregnant ladies Depending on whether it's a single or multiple pregnancy, after so many weeks a doctor's letter is requested. Towards the very end of the pregnancy the patient isn't accepted for travel. I haven't mentioned weeks, as it may well very from airline to airline.