Originally Posted by JustAnotherNigel

The line up bong is indeed manual upon line up clearance. It’s one switch movement, so you should get two chimes. Four is likely someone forgot if they did it or didn’t hear it and moved it twice to be sure. Far better than forgetting or zero. One is sometimes got if you move it too quickly for the plane when it’s early and tired.

The after take off bong is indeed when gear goes up and associated when the emergency lights go out. (Chime is due to the change of light situation). As mentioned this is usually when the gear drops on approach and after the gear goes up on climb out.

It says it can be done by flaps subject to spec, but then if so, it should also stay on until flaps are up on the climb out to as it’s just to do with config on an either/or. I have tried to find if any at BA are unique and they aren’t appearing so - or at least I can’t with a quick search. All should do it with the gear… so I will try and do some investigating because you’ve got me curious now.

EDIT: I think it’s two separate things. There is an auto position on the seat belts sign (on some aircraft) that if we select flaps with them off, they go to ON and have a chime. So if flaps are selected before the 10 mins to landing - or indeed we have forgotten to turn the belts on. They will go on with a chime at flaps selection.

Did you happen to notice if the flaps caused the seat belts to come on when you had that chime at flaps selection?