On Tuesday, August 16, 2016 at 7:40:38 AM UTC-4, wrote:
That's very interesting... where can one find this 'History'?


On Monday, August 15, 2016 at 6:33:59 PM UTC-4, FZ wrote:
There is a history of collapsing of the back rest in SZD-55.
Mine was equipped by the previous owner with a custom made wood inserts, supposedly preventing of such events. Collapsing of the back rest would certainly cause pilot to fall back and sudden back pull on the stick.
Following stall would be consistent with this scenario.

If my back support was being reinforced with wooden blocks I would assume something was broken and it would not be flown until fixed!

Regards,

Bob 7U

We are not talking here of some broken parts or wooden blocks.
The back-rest is adjustable by moving of two rails into one of few positions/cutouts/notches. Fixed pins go into notches and should stay there by the virtue of two springs pulling the rails downward. Sit stays put.
Given some unusual movement of pilot ( see dropped wing twice, some action inside a cockpit) it may happen that the springs are not pulling the rail strong enough to keep the rail in the selected position.
To prevent this from happening you will insert into the rails two long pieces of plastic or wood of certain shape. It positively prevent the movement of rails and back-rest.
I don't know if this is a factory part or some custom made improvement. SZD manual do not say anything on sit adjustment. It would be a good idea to ask the manufacturer.