I rather liked the Trident "Triplex" system where there were three of everything...Each radalt or AP monitored the other two...If it saw that it was significantly different from the other two then it dumped itself and a Red Flag would come up on the glare shield saying "MAN LND"...Autoland was not permitted with duplex but an Autoapproach was allowed but with a higher "Decision Height".
Seems to me that Duplex does not have the safety of Triplex...One of only Two is different, but which one is wrong? On a Duplex system with an error in any one the whole system should be dumped in favour of manually flying
