[t0mas88]

The probability is much higher in terminal airspace because all planes are going to or coming from the airport so they are on converging paths by definition.

And better GNSS based navigation equipment is now making it more likely than 20 years ago. The historical accuracy was such that planes where often a bit offset left or right off the route giving extra separation. Now the accuracy is so good that planes going opposite direction on the same route are passing exactly bang in the middle on top/below each other.

[KuiN]

The ability for planes to follow these highly accurate common flight paths was a contributing factor in the Gol flight 1907 mid-air collision in Brazil [0]. (That, plus ATC clearing the two planes at the same altitude _and_ both having TCAS (Traffic Collision Avoidance System) switched off). William Langewiesche published a great long-form article about the disaster called "The Devil at 37,0000ft" that's well worth reading if that's your sort of thing [1].

[0] https://en.wikipedia.org/wiki/Gol_Linhas_Aéreas_Flight_1907

[1] https://www.vanityfair.com/culture/2009/01/air_crash200901

[randompwd]

That vanity fair article was a good read but I felt it continually excused the American pilots ineptitude but happily pilloried the Brazilian air traffic controllers.

[throwawaygimp]

Yea, this is a really good point that isn't well known.

We've improved GNSS significantly, but the technology to avoid collisions hasn't been widely deployed, even though it's orders of magnitude less complicated than high accuracy GNSS on the whole

So... a random dilution of precision generator could... save lives? ha.

[t0mas88]

It's not uncommon in uncontrolled airspace to set a 1 or 2 Nm offset to the right in the FMS. Then it will follow the high accuracy path but not the same as opposite traffic that's 1000ft above or below.

[mnw21cam]

Planes going opposite directions on the same route are meant to be at different altitudes. Altimeters have been quite accurate for a long time.

[t0mas88]

1000ft separation isn't much when you have an issue, if you loose an engine at cruise altitude you typically cannot maintain that altitude for example.

Oceanic procedure, without radar control, is to turn 45 degrees off track while descending, but it takes a little bit of time to set all that in motion when things go wrong while you were just seconds before happily cruising straight ahead on autopilot (autopilot is mandatory above 29,000 ft in a lot of airspace)