What was found
WING MID-CORD RIB JUST FORWARD OF THE OB AILERON HINGE, FOUND CRACKED WHERE IT IS RIVETED TO THE REAR SPAR. BOTH LT AND RT SIDES SAME. THIS IS NOT EASY TO SEE DUE TO THE POSITION OF THE EXISTING INSPECTION HOLES BUT CAN BE SEEN IF YOU ARE LOOKING FOR IT. SB ADDRESSES PROBLEMS WITH AILERON HINGE BRACKETS AND REAR SPAR CRACKING IN THIS SAME LOCATION AND DUE TO THE SAME STRESS. PROBABLE CAUSE IS REAR SPAR TWISTING DUE TO AILERON LOADS. A VERTICAL STIFFENER AT THIS LOCATION WOULD REDUCE THIS LOAD TO THE SPAR AND RIB. (K)