BUSS is quite simple actually. It uses raw AoA from the vanes. There is no speed displayed, just an AoA range. Just keep it in the green. Combine with an appropriate thrust setting and you get expected performance.
Excellent - my question is then - why do the pilots have to deactivate a load of primary instruments to get this information?
You'd think it should be displayed as primary info.
AoA vanes are also prone to unreliable data. A vane might bend if you have a birdstrike directly onto it. Then, when using AoA a primary info, you still need to realise, that something is wrong. This circles back to the biggest challenge that comes with unreliable data: the recognition that you actually have unreliable air data. Here only pitch and power will help stabilising the flight path. When this is done, you should troubleshoot and try to find out, which air data (including AoA) is ok and which is unreliable.
This is not easy, as unreliable air data sometimes does not look unreliable. Blocked pitot tubes will lead to changing speed information on the PFD, when changing altitude. You might end up at an altitude, where all IAS speeds are the same, but still, some are unreliable. By the way, computers will fail to identify the unreliable source (s) in that case.
I have had crews in the simulator that recognised having unreliable air data. They stabilised and flew pitch and power till landing, as all the values where so inconsistent and ambiguous, that they where not able to tell which air data was correct and which not. The combination of failures they had where not that realistic, but still, they had one system, which was not affected at all. They realised, that this one system might be correct, but they where not 100% certain and elected to disregard it.
BUSS is nice. But for me it is more like an instrument, where I can check the correctness of my pitch and power values. BUSS respective AoA is load factor dependent. When you do a turn and pull some more g-force than normal, you will end up in the red area of the BUSS. Therefore, even with BUSS, I fly primarily Pitch and Power. I also will not use more than 15° of bank, as this helps with the g-force issue. Also I will try to do everything regarding airplane control and configuration sequentially. This makes flying with BUSS much easier. So, BUSS is not the holy grail, but it is a very nice tool!
Unreliable air data is complex. Even computers fail to recognise certain failure conditions. I have read suggestions upstream of the thread, that computers should compare all IAS values. And as soon as one IAS differs from the other 2, this value should be rejected by the computer. But what if the rejected value was the reliable one and the other 2 have been unreliable together (e.g.taped static ports)? These problems are known to the industry. Does the industry have solutions? Some are available: BUSS or the A350 use of FADEC data for a speed indication. Still there is no holy grail fighting unreliable air data. Pitch and power is still the best and easiest method for pilots. In the sim the pilots fly the regular approach speed ± 2knots using pitch and power. This is good enough!