Multiplayer: two controllers, one sector
Multiplayer does not split the sector between players. Everyone works the same airspace at once, so coordination decides how far you get.
How a session works
Three ways in: create a room and share its name, join one by typing its name, or use matchmaking and take whoever is waiting.
Everyone sees the same aircraft, score and wave, updated thirty times a second from the server. Each player has a cursor colour set in their profile, and you can see where the others point and what they have selected. A plane tinted in someone else's colour is one they are working on.
The score is shared. There is no individual scoring in a room: the sector succeeds or fails as one, and the run is recorded against the session.
The failure nobody expects
New pairs rarely lose to traffic volume. They lose to both players fixing the same conflict in opposite directions.
Two aircraft converge. A climbs the northern plane, B descends it in the same moment. The commands land a fraction of a second apart, the second overwrites the first, and both players think it is resolved while the planes are still at the same level. Headings do the same: A turns left, B turns right, and the aircraft ends up on a course neither of them chose.
Divide the sector, not the tasks
Split the radar in half and take one side each. North and south, east and west, it does not matter as long as you agree before the first plane spawns.
Then you handle every aircraft in your half, including ones whose destination is in the other half. A plane crossing the midline becomes your partner's the moment it crosses, and selection is visible, so you can check whether they already took it.
Splitting by task instead ("you do altitudes, I do headings") fails, because both jobs land on the same aircraft at the same moment.
Before you touch an aircraft, check whether it is already tinted in your partner's colour. If it is, leave it: your command would only overwrite theirs.
Handing over at the midline
An aircraft approaching the midline should arrive in your partner's half already set up: pointed roughly at its exit, on a sensible level, not in conflict. Dumping a plane across the line at the wrong altitude on a converging track is how sectors collapse at wave 10. With voice chat, the handover is the thing worth saying out loud.
Rooms and sessions
A room lives while players are in it. Empty rooms are cleaned up and a session idle for an hour is closed, so no name is held forever. To play the same sector with the same people, recreate the room with the same name.
Spectators can watch without controlling anything, and anyone in the session can promote them to a controller. Watching a good player for two minutes teaches more than this guide does.