RTQ....
What is his WEIGHT, not how many G can he feel, or what is his mass.
His Mass remains 100 KG.
The G force he can feel:
- We can not tell, without knowing the aircraft speed / Earth rotation issues - but then again the question told us to ignore them.
- But it would be less than 1 G, because an aircraft in 'straight and level' flight is not actually moving in a straight line and hence the forces on the aircraft are not actually in balance, nor are they on the Pilot.
- The Pilot would experience the sensation of slightly less than 1 G, because the force holding him up (an upwards push from the seat) would have to be less than his weight in order for him to accelerate downwards enough to follow a curved path of constant altitude around the earth.
- Taken to an extreme, a la Old Smokey, a space shuttle crew in orbit *feel* weightless.
- However, since you can only sense your weight when there is something present to hold you up, the term 'weightless' in that context is a misnomer / bad physics. They are in Free Fall, but their weight remains very much present.
The Pilots Weight:
- is however slightly less than at the surface of the planet by virtue of an increased distance between centres of mass involved, A La Enicalyth. Assuming the maths given by Enic was correct, then the gravitational field at 50,000' is 9.95 Newtons per Kilogram, yielding a weight of:
995 Newtons
(Onan has a point but I'm ignoring it as there is no data in the question to support it)