On April 8, 2011, about 1620 central daylight time, a Cessna 560XL, N547CS, while climbing after departure, experienced a loss of elevator trim control near Abbeville, Louisiana. The captain declared an emergency and diverted to the San Antonio International Airport (SAT), San Antonio, Texas, for an uneventful landing. The two airline transport rated pilots, the sole occupants on board the airplane, were not injured. The airplane was registered to and operated by CitationShares Sales Inc., of Greenwich, Connecticut, and doing business as CitationAir under the provisions of 14 Code of Federal Regulations Part 91 as a positioning flight. Visual meteorological conditions prevailed and an instrument flight rules (IFR) flight plan had been filed for the cross-country flight which had departed the Louis Armstrong New Orleans International Airport (MSY), New Orleans, Louisiana, at 1450, and was en route to the William P. Hobby Airport (HOU), Houston, Texas. According to the captain, the take off was normal and the climb was uneventful to 23,000 feet. About 1,000 feet below their cleared altitude, both pilots noticed an abnormal feel in the controls. Thinking perhaps the autopilot had disengaged, the captain verified that it was still connected. Approaching 23,000 feet the pitch trim annunciator came on. The captain disconnected the autopilot and felt the airplane’s nose immediately pitch up. The captain immediately controlled the abnormal pressure and attempted to reduce the control forces via the electric and manual trim to no avail. The pitch trim wheel spun without effect or friction. The captain slowed the airplane to the speed at which it was trimmed and ran the checklist for jammed elevator trim. The captain notified his company dispatch and declared an emergency with SAT approach control. The captain did a controllability check to insure no other control issues existed. He then flew a long final approach to an uneventful landing at SAT. A postaccident inspection of the elevator trim system revealed that the aft elevator trim cable had separated in two parts. The fractured cable was retained for further analysis. The cable pieces were examined in Wichita, Kansas, on June 16, 2011. The fracture occurred 11 inches from the roller chain that tracked through the elevator trim actuator. Using a scanning electron microscope, the examination showed fatigue failures in the individual wire strands. At high magnification, slight wear of the wire surfaces was observed. The cable was originally installed on the airplane at the time of manufacture. At the time of the incident, the cable had a total time of 5,445.3 hours. Cessna Aircraft determined that a cable with improved rope wire material was required. On April 9, 2012, they issued Service Bulletin SB560XL-27-34 requiring replacement of the elevator trim cable with the new cable within 300 hours or 6 months from receipt of the service bulletin.