Basically the Airbuses(except the A350) had three pitot, static sensors providing airspeed input to three ADRs. But when all three have different values or one having failed the remaining two differ there was no other speed information independent of the Pitot static to assess the correct one or reject all three. The digital speed is a calculated speed from AoA, GW, load factor plus GPS inputs etc. which provides that independent measurement to select the correct ADR or to reject all and provide that speed itself to use. Makes life easier. Another example of automation taking over pilot function.
Last edited by vilas; 31st January 2022 at 06:20.