What was found
VERTICAL CRACKS FOUND INTERCONNECTING ALL FOUR BOLT HOLES DRILLED IN THE AFT STABILATOR BULKHEAD TO WHICH THE STABILATOR BEARING BRACKET ATTACHES TO ON THE RT SIDE. SUSPECT CAUSE: EXCESSIVE AIR LOADS ON THE STABILATOR DUE TO AEROBATIC MANEUVERS (HAMMER HEADS AND SNAP ROLLS), AND AFT BULKHEAD BEING OF INADEQUATE STRENGTH TO ABSORB STRESSES. SUBMITTER RECOMMENDS PERIODIC INSPECTIONS OF AFT BULKHEAD EVERY 100 HOURS OR MORE IF AEROBATIC OR REINFORCEMENT OF BULKHEAD (REFER TO FORM 337). TT ON AIRCRAFT, 3600 HOURS.