You need 3 for things that if they stop working the plane crashes.
This is more of a "if it stops working the pilots have to fly more conservatively until it is fixed" thing. It apparently is generally considered acceptable for such things to not have triple redundancy, as long as a failure will be detected so the pilots can deal with it. Two computers is good enough for that.
This is more of a "if it stops working the pilots have to fly more conservatively until it is fixed" thing. It apparently is generally considered acceptable for such things to not have triple redundancy, as long as a failure will be detected so the pilots can deal with it. Two computers is good enough for that.