Final answer:
The L/R TK PUMPS 1(2) in an aircraft feed fuel as needed to maintain balance within the aircraft's fuel system. They help prevent imbalances that can affect aircraft performance.
Step-by-step explanation:
The question relates to the operation of fuel pumps in an aircraft's fuel system. Specifically, the L/R TK PUMPS 1(2) refers to the left and right tank pumps 1 and 2. These pumps feed fuel from the tanks into the engines or to other tanks to maintain balance. The correct answer to when the L/R TK PUMPS 1(2) feed fuel is 'D) As needed to maintain balance.' The system is designed to keep the aircraft's fuel distribution even and prevent imbalances which can affect the aircraft's center of gravity and handling characteristics.
It's worth noting that the pumps may operate under various conditions such as during takeoff, descent, or when there is a fuel shortage in one of the tanks due to unequal fuel consumption or fuel distribution strategies planned by the flight crew. However, the primary function of these pumps is to ensure fuel balance throughout different phases of flight.