What was found
DURING INSPECTIONS OF UNDERSIDES OF STABILATORS ON BEECH SIERRAS, SUNDOWNERS, HAVE FOUND DEFECTS RANGING FROM WORKING RIVETS TO CRACKS IN LOWER SKINS. PROBLEM IS CENTERED APPROX 6 INCHES OUT FROM FUSELAGE ON BOTH SIDES. MECHANICS HAVE INSTALLED OVERSIZED RIVETS, ADDITIONAL RIVETS, PATCHES. BEECH ADDRESSES THIS PROBLEM IN SI 1167, OFFERS A P/N FOR IMPROVED AFT CENTER SPAR CALLING FOR NEW SPAR TO BE BONDED TO SKINS. REPLACED AFT CENTER SPARS, AFT LOWER SKINS ON 2 SIERRAS, IN ONE, SPARS CRACKED WEAKENED BY 0.250 INCH CHERRY MAX RIVETS AND TRIPPLING OF RIVETS. ORIG SPAR DOES NOT OFFER ENOUGH SUPPORT TO CONTROL OIL CANNING EVEN THOUGH EXISTING SPAR MAY NOT BE CRACKED, WORKING, OR OVERSIZED. (X)