Sim/graphics/animation/lights/airplane beacon light dir
RGB form a 3-part normalized direction vector - see PluginsAndObjects.
A is the index of the beacon.
Alpha is set to the beacon light brightness. RGB is set to white.
This light will flash with the beacon.
This provides an airplane-mounted beacon with directional properties. X-Plane simulates 4 beacons - by default all 4 flash at the same time, which makes the beacon index unimportant. However if a plugin takes over beacons, this can be used to differentiate them.