Thanks a lot violetrose.Hi krittim,
This is my understanding from what I found out when I wanted to travel recently.
1. Your 475 visa is the substantive visa which means for as long as it is valid you can travel in and out of the country on your 475 visa. You must be back in Australia before the 475 visa expires.
2. BVA commences after your 475 visa expires to allow you remain in Australia while your application for 887 is being processed. When you do travel overseas on your 475 visa while your application is being processed, the BVA will cease, which means upon your return you MUST apply for BVA again BEFORE your 475 expires, otherwise you will become illegal.
3. If you want to travel when your 475 has expired or is close to expiry; you must apply for BVB and return to Australia before the BVB expires. Once you are back your BVB allows you stay in Australia the same way the BVA does, so no need to reapply for BVA. If you are outside Australia when BVB has expired, you cannot return. So be careful to give yourself enough time for unexpected delays. Once the date on the BVB has expired and you want to travel out of Australia again, you will need to apply for another BVB
4. Travelling overseas during the subsistence of your 475 / BVA or BVB does not require you to reapply for 887. Your 887 application is still valid and pending. Just don't get stuck overseas without a valid visa cos 887 requires you to be onshore for them to process the application and if you are not, they might refuse it.
Since your 475 visa expires only in May 2014 and based on the current processing times of 6-7 months from the information on this forum, your 887 application should be called up within the next 2-3 months, so I would not worry too much about the 475 visa expiring. If you do travel, just be sure that when you come back you reapply for BVA just to be on the safe side, it does not cost anything.