I interpreted it as the seat needs to press into the pilot in order to keep him in the loop. I wrote in an edit that the book does give D as the answer and gives the explanation that gravity and the normal force from the seat provide the centripetal force. I'm pretty sure the book is wrong, but...
Homework Statement
A pilot of mass m flies a jet plane on a "loop-the-loop" course by flying in a vertical circle of radius R at a constant speed v. The force that the cockpit seat exerts on the pilot at the top of the loop is
(A) mg.
(B) mg\left(\frac{v^{2}}{R+1}\right).
(C)...