Re: Windscreens
Most of ours are glass but I have seen at least two without. The scratches from the wipers are the biggest problem with those non-glass types from what I can see.
As for the cracking; I can't speak from experience on the AW139s but I have seen a bad batch of UH60 glass from PPG in the past. During one 45 day training exercise in the California desert we replaced around 15 (I think it was more) panels, one day after the next, both LH and RH on multiple aircraft. At first we were thinking it was caused by intense heat changes inside and out but we ruled that out, then we were afraid the install procedures/shimming was being done wrong, ruled that out as well after having a dozen or so people involved in supervising the process. Eventually chocked it up to a bad batch. We eventually got through that batch and never had problems again.
As for the pitting; Some of our S76s have glass that is so old that you can see micro pitting and scratches across the whole panel, looks as if its been on there for 20 years or more. It is not noticeable unless you really look up close though. Now that was a good batch of glass!