What was found
FLT 312 - KPHL-TJSJ - AFTER TAKEOFF AT FL 180, THE AUTO PILOT DISENGAGED AND THE STABILIZER TRIM JAMMED AT 5 DEGREES NOSE UP. THE FLIGHT CREW DECLARED AN EMERGENCY AND RETURNED TO KPHL. THE STABILIZER TRIM BECAME OPERATIONAL ON APPROACH AT 700 FT AGL. THE AIRCRAFT LANDED WITHOUT INCIDENT. A STABILIZER SYSTEM INSPECTION WAS PERFORMED. NO DISCREPANCIES WERE NOTED. THE JACKSCREW AND GEARBOX WERE CLEANED LUBED, AND AIRCRAFT RELEASED FOR A LOCAL ACCEPTANCE FLIGHT. DURING THE ACCEPTANCE FLIGHT AT FL 180, THE STABILIZER TRIM JAMMED AGAIN. THE CREW DECLARED ANOTHER EMERGENCY AND RETURNED TO KPHL. THE A/C LANDED WITHOUT INCIDENT. (M)