Some feedback: problem now resolved.

Hannah at SkyDemon Support very promptly advised the following:
"It's a good idea to check to make sure that the SkyDemon app itself is online:  Open the Setup menu and tap Connectivity Options, and in this window you'll see two options for live data. If you select 'Live Data when Planning' then SkyDemon will be online in planning mode, but will switch into offline mode when you're in Go Flying mode. If you choose 'Live Data when Planning and Flying' the app will always be online, whether you're in planning or flying mode.
It's also worth double-checking to make sure that your iPad has a good wifi or 3G connection." 

I did that, and all functions are now back - I'm WELL impressed with the support afforded to my probably very stupid question.  Thanks , Hannah!.

Phil 

My SkyDemon, running in a 3g iPad Mini has stopped reporting NOTAMS, or Wx. It worked fine on a trip last week, but now when I've plotted a route, selecting the NOTAM tab reveals a blank NOTAM page, with a message: "Your NOTAM briefing will appear here when you have plotted a route, or specified a search area". I thought I had, but clearly not!   The Weather page reacts similarly.

I'm new to both iPads & SD & I'm a non-techie.  I realise it's probably something I've done wrong, but I can't find what that is.  Please can anyone advise if there's anything obvious, and also confirm the basic iPad settings, eg 'Mobile Data', etc?

Grateful for any help, and sorry to be a numpty!

Phil