Thanks vilas and everyone, I appreciate it is a bad idea to turn back on ADR's that you are unsure if still faulty. My question was more about the system recovery if they were fine and you were to turn them back on.
My scenario given above is probably not that clear or practical - I've had a bit more of a think and I'll try another one, in conjunction with this excerpt from the FCTM:
IN-SERVICE EXPERIENCE OF HIGH ALTITUDE PITOT OBSTRUCTIONS
Analysis of the in-service events shows that:
- The majority of unreliable speed events at low altitude are permanent situations, due to the obstruction of pitot probes by rain, severe icing, or foreign objects (refer to the table above).
- At high altitude, typically above FL250, the cases of unreliable speed situation are mostly a temporary phenomenon: They are usually due to contamination of the pitots, by water or ice, in particular meteorological conditions. In-service experience shows that such a contamination typically disappears after few minutes, allowing to recover normal speed indications.
Let's say we are climbing through a layer of severe icing and the speeds go haywire. We apply the UNRELIABLE SPEED INDIC/ ADR CHECK PROC up to and including turning off 2 ADR's. We then clear the icing and do not expect further icing for the remainder of the flight. Do we continue like this until through FL250 on descent, turn off the last ADR and fly the BUSS, or could we while at a safe altitude, have a look at turning some ADR's back on?
If so, how would the systems recover?