Do I need a backup or extra subscription ?

Here's the summary of what CASA have told us:

For PRIVATE flying, the minimum legal requirement to satisfy CAR233(1)(h) is 1 iPad mini or larger. The legislation doesn't specify a minimum size but CASA have indicated they don't believe the iPhone is big enough. CASA have indicated in the CAAP233-1 (recommended reading for Private pilots) that a 200mm diagonal screen size (or larger) is ideal.

Note: in order to comply with the legislation your iPad MUST contain the maps & charts applicable to the route being flown (plus alternates). In practical speak this means if your iPad goes flat or fails airborne, or your subscription to OzRunways has expired or you don't download the maps/charts (in OzRunways->Settings->Downloads) before flight, you could be in breach of the legislation. And potentially stuck without maps/charts. CASA have indicated that if you are ramp checked and can produce a working iPad with working maps/charts, then you should be fine.

Of course for your flying type (IFR vs VFR), route familiarity, weather, terrain, experience and trust of iPads, you may like to carry two iPad's or paper backups. Given the additional level of safety this is always encouraged if resources permit. See below on how to add a 2nd iPad to your account.

For flying under an AOC (i.e. for a company), additional legislation (CAO 82.0 Appendix9) applies. CAAP-233 summarises how to set up an EFB. You will need a backup iPad or paper, a company EFB administrator amongst other things. The best resource to get started is the CAAP, then your local CASA representative. The minimum sized device is a screen 200mm across (diagonally). The iPad mini is good. For Android, the new Nexus 9 is also good.

When you pay for a basic OzRunways account it includes 1 tablet (e.g. iPad or Nexus9) & 1 phone (e.g. iPhone, Nexus6) to start with. You can add a second tablet personal backup for only $20 by adding that as a product on your account page, here:
https://www.ozrunways.com/store/account.jsp

If you are a company that requires 10+ devices and would like them billed in aggregate, please contact us at help.ozrunways.com or support@ozrunways.com -- For medium/large companies billed annually we can also set it up so the subscriptions NEVER expire to provide an added level of safety.

If your subscription expires whilst outside of internet coverage, you can activate 'emergency mode' in OzRunways->Settings. This makes all your subscriptions work for 3 days until you can reach an internet connection to subscribe for another year. You can use this feature once per device per year. There is no way we can reset this limitation.