a) There is change in direction in the direction of acceleration (perpendicular to velocity) . There is no acceleration in the direction of velocity and hence uniform speed (magnitude constant)
b) lift force and weight act on aeroplane and the resultant force is the centripetal force . A diagram showing lift force and weight that enables the plane to turn(banking needed)
The weight of the satellite provide the centripetal force. A diagram showing weight of satellite towards the earth and satellite orbit.
c) The resultant force of aeroplane is zero when it circle the Earth (L=W, T=D) and hence it is not orbiting.
To orbit is to free fall towards earth and the acceleration is g and the resultant force on the satellite is weight.