T&T: Comparing boat and aircraft autopilots

[John Baker]

I'd have to say that aircraft auropilots are definitely more hearty.  The 757/767(and others in their class) are able to land in absolute zero visibility(Cat 3b autoland) due to the fact that there are three autopilots controlled by three totally seperate computers which are powered be three totally seperate power sources(all bus ties open at about 1500ft) which are actuated by three totally seperate hydraulic systems(called "fail active"...will still be able to autoland if an autopilot is lost/inop).  The only reason there are published visibility minimums on a Cat3b approach is due to the capability of the airport(ie lighting systems) to get the aircraft off of the runway and to the gate.  Aint no use to get the aircraft on the ground and then not be able to find the gate....or find their way off the active runway..  The 737s have 2 autpilots,etc. and have to adhere to Cat3a(they actually have to see the runway environment in order to make a decision to land).  Transport
 category aircraft autopilots are serious hardware.
  Aircraft autopilot s also use totally seperate servos and actuators(dunno about them FBW aircraft) than the ones that are normally used to controll the aircraft by the yoke. 
  Now an autopilot you would find in a Cessna 172 would be much closer to what you'd find in a boat....it is more of a luxury whereas it is a necessity on an airliner.
   
  Trawler on,
  John
   
  PS....If it aint Boeing, I aint going!!!!

       
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