While TCAS priority was the technical point of failure, I feel that the transition phase from public to private of the Swiss air traffic control services in 2001 seems to be the greatest disruption of this finely coordinated ATC.

Under the new management of Skyguide which led to the obvious cut in labor cost like reducing the night shift from 3 to 2 controllers. The private company still tolerated the extended break convention during night shift from before but leaving only one person responsible, now. And guess what? Maybe a software update to make some efficiency steps when we are at it. The single one controller was then informed during the update taking place what was still functioning and not which was very little.

>Part way through Nielsen’s shift, a group of technicians arrived to install the update, and he was informed that his work station’s main computer would have to be shut down, causing his displays to operate in fallback mode — a secondary condition in which several features provided by the main computer became unavailable. In fallback mode, the system which automatically correlated an aircraft’s radar return with its filed flight plan would not work, forcing him to enter the information manually, and the Short-Term Conflict Alert light, which illuminates when the system predicts that two planes will pass too close, would be rendered inoperative. But Nielsen had no idea what features would be lost in fallback mode, nor did he have any obvious way of finding out. And as if that wasn’t enough, a few minutes later the technicians informed him that they would also have to disconnect the control center’s direct telephone landline to neighboring centers

For me also surprisingly shocking that back in Karlsruhe multiple (!) controllers had to literally watch the obvious horror unfold while the one controller responsible was not available because of ... maintenance work.

>Heartbreakingly, controllers in neighboring Karlsruhe saw the collision coming, but they did not have the authority to speak to planes in another sector without permission from the responsible controller. The Karlsruhe controllers tried several times to call Nielsen in the minute before the crash, but the landlines were down and they couldn’t get through. By the time they gave up on this effort, it was too late to prevent the crash even by breaking the rules. The controllers were forced to watch, helpless, as the two planes collided and then disappeared from radar, knowing that dozens of people were dying before their eyes, and that there was nothing they could do to save them.

Edit: According to this article [0] and this verdict [1] the controllers in Karlsruhe had the full authority but were illegally instructed otherwise by DFS (German ATC) management which had an informal agreement with Skyguide (Swiss ATC) over this border region.

In the end the heavily traumatized and retired controller Nielsen was brutally stabbed because the modern diffusion of responsibility of companies only operates on the culture of financial compensation and is blissfully ignorant of a desperate man losing his whole family trying to restore his honor. So, no apology before everything is settled accordingly.

[0]https://www.dw.com/de/deutschland-haftet-f%C3%BCr-fehler-der...

[1]https://research.wolterskluwer-online.de/document/2ceee0e8-5...