Steve Kroop at Flytec USA ()
writes:

Recommendation to all pilots flying tandem gliders utilizing
landing gear: Routine inspections of keels and control frames should be
performed to look for evidence of metal fatigue and/or fracture that may have
resulted from hard landings and/or taxing over rough ground. This may not be
evident on routine pre-flights due to the placement of hardware, brackets and
hang straps, etc. Proper inspection may require glider disassembly and as a
minimum should be conducted at annual inspection. Particular attention should be
paid to bolt holes and surrounding areas where the control frame, king post and
tail wheel extension attach to the keel, as well as the region of the keel where
the crossbar passes over the keel.