For the past week I have been watching my DVD's of La Sylphide---5 different productions....In all of the productions the Sylphide's wings appear to fall off without any human interference...how is this accomplished?...does she push a button somewhere??

In the RDB production (and those derived from it) I believe there is a button in the front of the bodice which she pressed to make the wings fall off.

Editing to add (noted in my post below) that it's not a button but a key that the ballerina turns.

I have sometimes seen little strings on the front of the Sylph's costumes, near her shoulder straps. In the death scene, when she turns her back to us and embraces herself, she seems to pull the strings to release the wings. This is probably more visible from seats upstairs, and it can easily be discretely obscured by a camera.

I've often wondered if she wears different wings (or whole bodice?) in Act I and Act II, so the wings remain secure in the first act.

if memory serves, fracci's 'pull-cords' were fixed with teardrop-shaped pearls on which she tugged delicately to activate the release of the pins that secured the wings on her back. too often though they wouldn't fully drop off fully or get caught in the scarf...

I watched Martine Van Hamel coach Ashley Tuttle in this scene, and she mentioned the strings that carbro wrote about. Not sure about the different wings/bodice, although that sounds plausible, as Van Hamel said every now and then a string would break and a wing would come off too early!

I'm correcting myself. It's not a BUTTON, but a key that the ballerina turns. Don't know about any strings

I don't know why, but that's very funny! Like a clockwork ballerina with a key in the front! I wonder how it remains hidden. It must be a really, really tiny key. I have noticed the strings, although I have no idea how it works.