Abstract: A method, apparatus, and system for testing a fuel tank for an aircraft. Electrical power is sent to an optical data concentrator for the fuel tank for the aircraft from a power supply such that the optical data concentrator sends optical signals to optical sensors inside the fuel tank through optical fibers connecting the optical data concentrator to the optical sensors. The electrical power is sent during a phase of manufacturing of the aircraft. Test data is received from the optical data concentrator by a computer system. The test data is based on optical response signals received from the optical sensors. A determination of states for the optical sensors is made by the computer system using the test data. A graphical indication of the states determined for the optical sensors inside the fuel tank is displayed by the computer system in a graphical user interface on a display system.