Finn350 wrote:osiris30 wrote:estorilm wrote:Exactly - there's a specific reason for having more than two. Guess who has used three on all aircraft for over 30 years now?
And even that is far from foolproof. You could have 100 and still have weird corner case failures. Not that I am defending a single point of failure system but one thing that people do have to remember is it's not just the cost of the part. It is all the maintenance that comes with adding even more parts. You could put 50 aoa sensors on an aircraft and have an amazing chance of always having good AoA readings, but you'd have to maintain all 50, which would be a nightmare and very costly. 2>1 at least you can see a discrepancy. 3>2 it allows a bit more trust in the system (but still has well-known failure cases that have ACTUALLY happened). 5>3 your odds improve, but you could get into a situation where you have 2+2+1 readings based on specific conditions I could see happen. Realistically you would need around 10 to get to a point where you could call it 5 9s.
I am quite sure that with 3 vanes we are already well above 5 9s (or failure in less than one in 100,000 flights).
Spent too much time doing 5-9s work, 3 is not 5-9s. This isn't a case where you need 1 system functional. You need a minimum of two functioning. 3 isn't even fully redundant for the minimum number of sensors needed. If one fails hard and one gives erroneous data you are screwed. I can conceive of many situations that would take out two sensors, and in fact we have records of such happening. There is no way from a qualification standpoint 3 sensors is 5-9s.