What was found
DURING TEST FLIGHT AT 15,500'& 180 KTS, SLAT HANDLE MOVED TO EXTEND POSITION, SLATS WOULD NOT EXTEND. HANDLE MOVED BACK TO RETRACT & EXTEND AGAIN, SLATS FINALLY EXTENDED NORMALLY. HYD PAGE INDICATED NO QUANTITY,"HYD 3 FAIL" THEN DISPLAYED. COMPLIED W/RED TABS AND MADE UNEVENTFUL LANDING. FOUND LH OB SLAT DRIVE MECHANISM FAILED AND HYDRAULIC LINES RUPTURED.REMOVED AND REPLACED LT OB SLAT DRIVE MECHANISM IAW AMM 27-83-02-1. REPAIRED HYDRAULIC LINES IAW AMM 20-10-01-2 ON SNR S0009 WRI 29-10/7212.MINOR REPAIR.LEAK AND OPS CHECKS GOOD.