upvc windows dropped

[Natto]

All of my upvc windows have dropped.
They are all top hung.
On investigation, the screws holding the hinges on the opening sash were loose, I tried tightening but the screws only go into plastic, I can't see or feel any reinforcing inside and there is nothing on the outside, just upvc, so a 1m x 1m window is being held by 3 screws either side only into upvc, is this normal ? And how can I solve it ?

 

[Gazman16]

Yes its normal (scary isnt it!)
The have most likely dropped on the sash rather than the frame though, Usually you need to take the sash out to adjust.
For the frame fixings if they are loose and just turning switch them out for screws with a slightly bigger thread, Dont over tighten them