what conditions are acceptable, and what medical conditions should be avoided, not only to safeguard the sick person but the aircraft itself.
I have never seen any guidelines from the CAA
I don't think there are any "
guidelines" from the CAA on this particular subject. My general feeling about this is that any Commander of any aircraft must exercise Common Sense and Good Airmanship. Adherence to those two will avoid or resolve most of the likely pitfalls.
I would hesitate to be drawn on which medical conditions are acceptable and which should be avoided. From a physiological point of view a quick local jolly in a C172 is really no more likely to be harmful than a ride in a car in the Scottish Highlands ( ie similar altitude AMSL !).
My greatest worry, which has been referred to previously, would be that the PIC's total control of the aircraft was, in any way, impaired. Slumping over the RHS control yoke in death is a very extreme example.
The PIC's movements may be limited if the person in the RHS is extremely obese - I have personal experience of that one ! Mental capacity to obey instructions, and NOT touch anything, could also be very important. You can just see it, can't you . . . . . "
What does this lever do, then ?" as he unexpectedly retracts your flaps on very short finals !
I think I'll stick to my regular passengers most of the time !