We had to close our sky several times during those last 4 years (meaning no aircrafts allowed above the country). Several times for technical failures, the last one this summer wasn’t our fault but was cool.

I arrived at work for a night shift in the ACC (area control center), heavy rain above the city, I see a small lake forming up against the building underground.

When I reached the elevator, I took off my EarPods and heard a shower like sound coming from the elevator. Eh let’s take the stairs… Curious, I venture to the underground where I’m greeted by a bunch of laughing air traffic controllers and the ACC supervisor for the night. There is something like 40cm of water everywhere, blocking access to the -1 floor and our smoking corner. We joke about doing the "clear the sky" procedure because we can’t use the smoking corner.

A few minutes later we are all back in the ACC, I wasn’t seated yet when the crisis phone rang: We mobilize the board of crisis, reason is the flooding reached some electrical supply rooms, like UPS and batteries rooms.

30 minutes later the AC is down. AC for us humans in the building but mostly for the data center with all the ATC systems needed for our work. Some systems start to overheat and fail.

Less than one hour into my shift, the board of crisis that quickly assembled comes to us in the ops room and says: "We clear the sky, it’s too dangerous".

For us in air traffic control, clearing the sky is easy, you just tell aircrafts a heading to quickly get the fuck out of our airspace and then you stay in front of an empty radar screen. Capacity management people have a little bit more work to do, announcing Europe and Eurocontrol that our ‘capacity = 0 please don’t send traffic’. It’s the tech people that have a lot of work in those situations, personally I just sat on my ass making jokes and scrolling lemmy.

We ended up switching off all the unused screens, systems etc to avoid heat. Opened all the electronics hatches, all doors, everything we could do to have some fresh air inside as it was getting hot. Airport fire squad quickly came and pumped out the water from the basement. They did that all night until morning.

At the end of my shift at 6, temperature inside the ACC was 29 degrees C (instead of 23) and humidity % unknown but it felt "sticky". Sky was still closed. Apparently during the day it felt like a sauna.

The tech guys managed to restore some AC only for the data center and the ACC but not the rest of the buildings so it was mandatory work from home for non ops people. When I came back the evening for my second night shift, everything was back to normal for us and it was a sad normal night with no fun events.

It turned out that the flooding reached 40 cm on the -1 floor and 1m40 on the -2 floor. There is a small underground river below that with a pool that is used as natural cold water for AC. That cold pool was filled with hotter (and unclean) rain water, killing the cold production loop.