The Show Must Go On

In the analogue days, main TV transmitters were fed (still are) by two diverse 11kV feeds. There was one
exception, Bilsdale, that's so remote only one 11kV feed is possible, so it had uniquely a gas turbine genny
to back up BBC 1 and 2. A higher order failure (33kV or above) can lead to both 11kV feeds dying. That could well have been the problem at Black Hill. I recall it happening at Oxford about 10 years ago, and everything from there was dead for an hour or so, (mid morning, so no great disaster for TV)

It was usual for the Tx aerials to be shared, not everywhere, Mendip, Winter Hill, Emley and CP had separate
aerials for BBC1/2 and ITV/4, but Sutton Coldfield, Rowridge, Wenvoe, Bilsdale, Durris certainly had shared antenna systems.

Today, DTT transmitters have far lower power consumption, so as well as the diverse 11kV feeds, all 50 main sites have genny back up, for PSB and COMs

The original STV region had more than one transmitter didn't it? Why didn't they just continue on air for those viewers?

Unless of course they were seeing regular programmes and the emergency tape was coming from Black Hill

There also had Craigkelly and Davel,

Yes, Craigkelly and Darvel. Tony Currie can give us chapter and verse, but I think Darvel was fed by off air
link from Black Hill (as many 'secondary' main stations were). I've got a feeling that Craigkelly was line/SHF fed
from STV because it carried different ads ?

Unlike the Beeb, who had very extensive RBS back up systems, ITV and C4 didn't. In my part of the world in Hannington-land if Rowridge died (which it would often do) BBC 1 and 2 were back within seconds sourced from Crystal Palace, ITV and 4 just died (though towards the end of 90s, there was a back up off air link for C4 from Mendip (right ads unlike the much closer CP !))

If you believe Wikipedia, Craigkelly was RBL Black Hill originally, although it might have been line fed later.

If it was SHF is it likely that Black Hill could have been a midpoint so affected by the failure?

Quite likely !!

It seems that BBC 1/2 were SHF fed, 7 GHz SHF Rx here

http://tx.mb21.co.uk/gallery/gallerypage.php?txid=981&pageid=458

And Torosay which covers the inner Hebrides, Oban, Fort William and the extreme southern tip of Barra.

I remember a very odd moment at some point in the late 90s when the Granada News during GMTV came on and was presented by some random woman who had clearly never been on television before, was dressed in very ordinary clothes and was smiling a bit too much whilst barely reading the autocue. After the first report she had been replaced by a slightly less dreadful bloke who stumbled his way through the rest of the bulletin. I can only assume the newsreader had fallen ill or hadn't shown up and they'd grabbed someone from the newsroom.

Similarly, but less dramatically, when I did work experience at Calendar a few years ago the Daybreak newsreader was unaware that he was supposed to be working that morning and ended up sleeping through all three bulletins he was supposed to present. They just had to show Tyne Tees news instead.

Did you not volunteer?

I was in bed as well!

With the newsreader?

That's actually quite common on breakfast opt outs, the first one of the morning in particular is the most likely to be missed. There'll usually only be 2 or 3 people working on them and if one over sleeps then it can't happen.