What was found
DURING A D CHECK INSPECTION, FOUND HORIZONTAL STABILIZER RIBS CRACKED AT HSS 350. PERFORMED A BORESCOPE INSPECTION OF THE HORIZONTAL STABILIZER RIBS IAW CHAPTER 55-10-00 IN THE MODEL 400 & 400A MM. FOUND A TOTAL OF 7 RIBS WITH CRACKS, 2 45A2112-0005, 2 45A2113-0005, 2 45A21101-0011 & 1 45A21116-0005. AD 2014-15-15 & THE 400 & 400A AIRWORTHINESS & LIMITATION MANUAL, TACK CODE 045505 REQUIRE INSPECTION OF THE HORIZONTAL STABILIZER RIBS PRIOR TO THE ACCUMULATION OF 7,400 HOUR INITIAL WITH RECURRENT INSPECTIONS EVERY 2,400 HOURS.