Flying

So about 0.06% of their total flights?

I doubt you'll find many idiots working at GCHQ.  More likely some of the sharpest brains in the entire UK.  Have you ever seen some of the quiz questions they release for the general public from time to time?  They come up with them just for fun, in their spare time, as a hobby on the side.  More genius per square mile than almost anywhere in the country, I should imagine.  I think the only idiot here was the one driving his phone. 

Personally, I'm very grateful that our security services are doing their bit to keep us as safe as possible from the serious nutjobs within our country, as well as externally.  And I bet we only see a tiny handful of the potential atrocities they manage to thwart every year.  More power to their elbow. 

I have some first hand knowledge of that organisation and certainly was not implying that it as an organisation is a bunch of idiots. There are undoubtedly some good mathematicians there although harder to attract these days as finance is (far) more lucrative. I said "some idiot" likely getting excited about a private joke and sending up a military intercept. That "idiot" I referred to was likely not a mathematician but a decision maker probably a member of another security service.

A private joke is IMO just that. Whether funny or not is nobody's business IMO and certainly not worth spending 100K on. If we think its ok to use private jokes as intelligence, then if the technology exists (and who knows it doesn't?) to remotely acquire a person's dreams when he is asleep, then would it be ok to use those as intelligence too?

I find this not-dissimilar to cabin crew having planes diverted etc because they couldn't control a passenger. Yes there likely are some situations but there are likely many others whereby the person could be brought under control without turning the plane around or back to stand. There's a bit of "I'll show the bastard" which of course comes out as "...my training kicked in and we informed the pilot blah blah..."

What does "putting on the internet" mean ? Is sending a Whatsapp message putting it on the internet? What about sending a tcp ack packet to a random server? Is that "putting it on the internet" ?

I don't know instagram or how its private groups work.

But still you could answer the question about making a joke in real life totally in private. Should that be allowed ? Is it allowed?

I travel a lot less as I can only afford a few business/first class flights .
I'm nearly 6' and slim but leg room is a trial on long haul. 
Happy to pay out and now mostly travel by volvo or soft/first class rail in Europe. 
Elephant people should be culled,even if they are nice. Their overindulgence is a crime against humanity.

I'm no lawyer, so whether technically he committed an offence under the Telecommunications or Anti-Terrorism legislation is one for those better qualified.  However, the authorities are charged with trying to protect our citizens, so anyone idiotic enough to transmit electronically that they plan to blow up the plane they're just about to board might expect to get their collar felt.  It's known that they monitor comms for trigger words and no doubt couple with AI and other intelligence sources these days to get a fair picture of events and likelihoods. 

I'm sure he made his buddies laugh.  Let's hope he sees the funny side when he gets the bill for the F18s scrambled... 

Let me turn your question on its head and ask this.  Would you be comfortable if somebody succeeded in blowing up a plane, with hundreds of lives lost, having first discussed their plans by Snapchat, which the intelligence services were duly alerted to yet took no preventative action against because it was probably all just a big laugh?  I suspect you'd be complaining bitterly that they ignored the very compelling evidence before them and now all those people have perished.  So what should the intelligence services do exactly?

Personally, I'd feel safer if they continue to act on the side of caution and treat these events seriously.