>> The microcontrollers, running on PowerPC processors, received three commands from the three flight strings. They act as a judge to choose the correct course of actions. If all three strings are in agreement the microcontroller executes the command, but if 1 of the 3 is bad, it will go with the strings that have previously been correct.
This is a variation of Byzantine Tolerant Concensus, with a tie-braker to guarantee progress in case of absent voter.