Originally Posted by
Few Cloudy
As for the Air / Ground switching, I imagine that the good old WOW switch was thought old fashioned by the software boys.
Rather ironically given the current issue, WOW (prox sensors) was not considered sufficiently robust with regard to ElectroMagnetic Interference and is typically single thread. LRRA designed and certified as a Critical "DAL A" system and nearly always has redundancy.
When we did the 747-8, we used a combination of WOW and LRRA for critical engine control functions - basically five sources (two WOW, three LRRA) - to indicate "On Ground" for critical functions we required three on-ground indications, with at least one each from WOW and LRRA.