Hi Grant
I took my MBA back a claimed a refund under the UK's Sale of Goods Act as it was, "Unfit for purpose," and have since relied upon my my 17" MacBook Pro and an external battery pack. A much heavier solution.
I had two MBAs, one from 2012, the other from 2013. The 2012 version would crash whilst in a bag travelling back and forth between the train and office on London Underground.
The 2013 version behaved as yours. It was fine to begin with, then began to crash but at least recognised and error had occurred and reported it. This got progressively worse until it would crash without warning and without any human intervention whilst reading a document on the screen.
Apple replaced numerous parts, and the guys at the independent retailer used parts from their own machines after Apple ran out of ideas but nothing fixed it and I was able to demonstrate the crash on every one of the MBAs they had on sale - I also did this in the Apple shop until they intervened and threatened to remove me. I did ask why they would do that as I was only testing them to see if they worked?
It would appear an excellent product has been let down by poor quality components.
Meanwhile, after just 25 months, the hard drive on my MBP has failed. Luckily, I bought it for my business so purchased the extended warranty but it looks as if Apple's poor quality extends across its entire range as the screen and trackpad have already been replaced.
I have a 12 year old Compaq that is unusable as it is so slow. It's been everywhere, done everything and never let me down. I have a variety of other hardware that is equally robust, underlining Apple's quality issues that are totally unacceptable for a high end computer they are already over charging for.
I see you're in Australia. You have excellent consumer protection over there and the government's own experience of poor reliability lead to them forcing Apple to offer a 24 month warranty as standard.
I would advise anyone here to take their MBA back for a refund.
I would also advise people to join the Fac ebook group. Search for MacBook Air screen goes black and help publicly shame Apple into action.
Apple clearly don't give a hoot about their customers as they laugh all the way to the bank.
If large corporations used Apple, they wouldn't get away with it but as they've appealed to private individuals we have no way to bring pressure to bear and these forums are just an opportunity to vent spleen without embarassing Apple in public.
I have also left reviews wherever I can to further shame Apple and would propose all reading this and experiencing problems do the same. So few people bother leaving feedback it wouldn't take many of us to drag their scores right down and lots of people pay attention to that when making a purchase.
The only way Apple will put any effort into resolving this is if they think their sales will be affected.