Thanks a lot to all for the information,
do you know if there is any section of JAR describing the requirements for this document ,
many thanks
I'm flying A320
The information is found the individual aircraft's Structural Repair Manual on the "Neglagable Damage Limits" page of each chapter. Every aircraft is different, in fact the allowable limit varies between sections (skins/bulkheads/frames/ribs/etc) of the same aircraft. Therefore, I would doubt there is JAR on the subject and if there is, it would contain little useful infromation.