(Dean Wilkinson) wrote

Autoland is a triple redundant system and all three boxes have to
agree in order to autoland the airplane.

It might have been more correct to state that Autoland from a Cat III
approach is a triple redundant system. I have flown many Autolands
from Cat II approaches in B-727s with only one Sperry autopilot, either
the SP-50 or the SP-150.
It is true that this one autoland approved autopilot was equipped with
an additional "roll monitor" card that became active whenever the
autoland function was engaged and the aircraft was below 500'AGL and it
had two elevator channels, one controlling the left elevator and the
other controlling the right elevator.
But, there was still just one autopilot with just one power source and
receiving ILS signals from one LOC/GS receiver.

Bob Moore