For AF447 it was quickly established that airspeed sensors problems were probably responsible for the initial 'upset' and there was a programme to replace that type of (Thales) sensor - presumably successful? For the MAX, Boeing say that the MCAS system only operates when the aircraft is OUTSIDE its 'normal envelope' (or sensors suggest it is). In the recent accidents it seems that faulty AoA sensors caused the a/c computers to think that the a/c were outside of the 'normal envelope' and erroneously invoked MCAS. Seems to me that maybe the AoA sensors should perhaps be more the focus of attention - surely there must be alternative manufacturers for similar sensors?