scope:

Description of Driving Event:

During prelaunch check out of shuttle orbiter OV-104 for flight STS-36, the AC2 buss phase a voltage fluctuated between 112 and 122V for one minute. The inverter supplying that buss was removed and replaced. The vendors' inspection of the failed inverter found loose mounting screws on the electrical buss internal to the inverter, which caused the voltage fluctuations. An identical problem had been previously discovered that prompted a change to the manufacturing procedures to include a specified torque for the mounting screws. The failed flight unit had been reworked, but the manufacturing procedural change had not been incorporated into the rework process.