On Wed, 23 Jun 2010 16:35:56 -0700 (PDT), Judah Milgram
wrote:

snip

Most modern gliders are stressed to take at least +5.3/-2 g without
damage. A winch launch comes nowhere near this as long as the correct
weak link is fitted, which will break well before the glider does. I
believe that the glider that failed had being doing aerobatics
immediately before, which is a more likely cause of any
overstressing.

Derek C

If I recall correctly, the concern was with fatigue damage
accumulating at loads below the limit load. If fatigue cracks do form,
you could get a static failure below limit load - and not necessarily
during a winch launch. How serious this concern should be in the case
of the L-13 I couldn't say but given that they think it might have
been a fatigue crack, the AD seems pretty reasonable.

JM.

Actually and AD has not been issued by the FAA. A mandatory bulletin
from the manufacture has been issued. There is a huge difference. An
AD is mandatory in the US. A mandatory bulletin by the manufacture is
optional.