Tactile Check
A long time ago I was told that a visual check can confirm that there is contamination, but it can not confirm that there is no contamination.
Consequently, as positive confirmation of the absence of contamination is required, a visual check is not valid.
Only a tactile check will confirm the absence of contamination. The logic of this is missed even in the most detailed and latest references.
It follows that a check from the cabin or flight deck is invalid, except to confirm that there is contamination and that you need to de-ice, but it can not confirm that it is safe to go.
- A visual check is not valid -