Richie
In non-student situations, the person in the left seat is the PIC (Pilot In Control) and has the last say about a flight. Unless he/she formally turns control over to the co-pilot.
It's not that simple. The PIC (Pilot In
Command) can be sitting in any seat, including the potty seat in the back of the plane. When there is more than one pilot in a plane (Noonan was a licensed pilot) and there is an accident or an enforcement action brought by the FAA for violation of a regulation, the question of who
was PIC at the time always becomes an issue. In airline and military operations the PIC is designated in writing prior to takeoff and that paper is left behind. The person designated as PIC is still PIC even sitting on the potty or taking a nap in back. The PIC doesn't even need to be near the flight controls. Just letting the co-pilot manipulate the controls does not relieve the PIC from being PIC.
Don't confuse who
is PIC with an entirely different question of who may
log time as pilot in command which only requires being "the sole manipulator of the controls" so the co-pilot can
log time in his logbook in the "PIC" column if he is manipulating the controls even though he
is not the PIC.
It gets more complicated in informal flying situations and the person who is PIC may actually change during different segments of the flight. If there is a violation of regulations followed by an enforcement action by the FAA the two pilots usually argue that it was the other guy who was acting as pilot in command during that segment of the flight. There have been cases where three pilots were in the plane and the guy in the back seat, not near the controls, happened to also be a flight instructor. Even though it was not an instructional flight and the instructor was not giving instruction, the flight instructor has been found to be the PIC and responsible for the crash or regulation violation because the guys in front, manipulating the controls, testified that they would have asked the instructor if they had a question and would have done what he advised. This happened because those guys identified the guy in back as the person that they considered the authority for flight operations based on his superior experience and knowledge.
It is a different issue as to who was the pilot manipulating the controls at the time of the crash and this is often resolved by determining which body has the broken thumbs which resulted from holding the control yoke at the time of the impact.
Read Federal Aviation Regulation 91.3 (which I memorized 40 years ago), "The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft." Earhart was obviously the person with "final authority" as to the operation of the flight so was the PIC. But, if she if she voluntarily relinquished that authority to Noonan for a particular segment or if she became incapable of exercising that authority then, by default, Noonan would become the PIC.
gl