I’m not sure if I understood you, but I think you can build them whenever you want. They have to be constructed before you decide to handle baggage handling service for aircraft.
A tilt tray is used to split baggage down two different routes. You can theoretically send it in 3 directions (forward, left and right) but at the moment only 2 paths can work at any one time.
Build the tilt tray at the junction where baggage needs to head in two different directions (you don’t need tilt trays when merging conveyor belts.
If you right click on the tilt tray you can set it’s operating setting as one of the following:
To Destination: The tilt tray sends the bag in the direction it needs to go to reach it’s destination (baggage bay/claim area), this is the most useful setting
Forward & Left: The tilt tray alternates between sending baggage forwards or off to the left (in the direction of travel). This works if you have a branch going forward from the tilt tray and one going left. Use this if you have want to halve the number of bags going down a given path (such as through a set of security scanners) if they can rejoin later on. Do not use this to direct baggage to it’s ultimate destination.
Forward & Right: The tilt tray alternates between sending baggage forwards or off to the right (in the direction of travel). This works if you have a branch going forward from the tilt tray and one going right. Use this if you have want to halve the number of bags going down a given path (such as through a set of security scanners) if can they rejoin later on. Do not use this to direct baggage to it’s ultimate destination.
Left & Right: The tilt tray alternates between sending baggage off to the left and off to the right (in the direction of travel). This works if you have a branch going left from the tilt tray and one going right. Use this if you have want to halve the number of bags going down a given path (such as through a set of security scanners) if they can rejoin later on. Do not use this to direct baggage to it’s ultimate destination.
None: it operates like any other piece of overground conveyor belt (in one direction only and forward by default)