mrblampo

With the horrible news this morning about the American airlines collision with a helicopter near Washington DC, I am sure the biggest focus will be on how these two aircraft came to be perilously close together, but I am also wondering: Does anyone here know the state of collision avoidance technology in commercial airplanes? This is something that cars are starting to get pretty good at, at least fancy ones like Teslas (I know they make mistakes they still do an impressive job of detecting potential collisions and avoiding them). I imagine that this is a harder problem for planes.

When you pick up a landline phone, throughout the USA there is a consistent "dial tone" you hear in the earpiece.

I haven't heard it in a while, but IIRC it's two synthesized tones roughly a "major third" apart (https://en.wikipedia.org/wiki/Major_third), slightly buzzy-sounding, which means they probably weren't a "just" major third (https://en.wikipedia.org/wiki/Just_intonation).

Once you started dialing, the dial tone would go silent. I think the dial tone would remain in place if you spoke, but I don't remember for certain.

Does anyone know how this worked? What generated the dial tone? Presumably there must have been a network of machines responsible for processing people's dialing and routing calls appropriately; did these machines also generate the dial tone? If so, were they all made by the same company, Bell-something-something? The dial tone was/is so consistent in its sound and behavior that it seems likely.

Just curious if anyone knows or has links!

I.e. comments that are literal spam, from accounts I've never heard of, on documents I've never seen, but where I am tagged. And they always mention some Bitcoin transaction whose funds are now available, in or similar.

Has anyone found a way to make this stop?