Abstract: A backup navigation system that is failure resistant. The backup navigation ystem has a multiple member of navigation subsystems. The backup navigation system has the same multiple number of computers. Each computer has the same multiple number of computer processors. Each navigation subsystem is connected to only one computer processor of each computer. Each computer selects data from one of its computer processors in preference to data from any other of its computer processors. Each computer provides a navigation output. Each navigation output is sent into a control navigation computer. One of these navigation outputs is selected by the control navigation computer. A navigation output from one of the computers can also be selectively sent into a navigation interface buffer.