Yes well.....
One main reference to ground maintenance procedures with no actual guidance at all, plus a few oblique references. Main emphasis as far as detection goes placed on flight crew. Baloney! As was reported by NASA, you can fly a DC-8 through thick ash that does $2m+ worth of damage and make no useful observations at all, of instruments or out the window! And then the crew (not, I think, ground engineers) do a Mk1 Eyeball check after safely landing, and STILL find nothing. And these guys KNEW there had been an ash encounter because extra (scientific) instrumentation on board had detected SO2. Do you think that given these (well-known?) facts, the Mk1 eyeball is enough as Step 1, given that you say additional checks depend on Step 1 finding something?
To quote from the NASA DC-8 Incident Report:
There are currently no fully reliable methods available to flight crews to detect the presence of a diffuse, yet potentially damaging volcanic ash cloud.
I know of no changes from that position since 2003.