On May 15, 2004, approximately 1350 central daylight time, a Lockheed 1329-23E turbojet airplane, N57NR, sustained minor damage following an in-flight separation of the left flap assembly while on final approach to the William P. Hobby Airport (HOU), Houston, Texas. The airplane was registered to and operated by Aircraft Trading Center Incorporated, of Tequesta, Florida. The two airline transport pilots and two passengers were not injured. Visual meteorological conditions prevailed and an instrument flight rules (IFR) flight plan was filed for the 14 Code of Federal Regulations Part 91 business flight. The cross-country flight originated from the Corpus Christi International Airport (CRP), near Corpus Christi, Texas, approximately 1315, destined for HOU. According to the 12,500-hour pilot, as the flaps were extended to the full flaps position on final approach to Runway 4, the airplane decelerated and rolled uncontrollably to the left. The pilot stated that he regained control of the airplane by "accelerating to approximately 165-170 knots and holding right roll control." The aircraft landed without further incident. A post-flight inspection of the airplane by the crewmembers revealed that the left inboard flap had separated and the attach bolts were still in the flap attach brackets. The pilot added that the airplane had accumulated approximately 13,534.8 flight hours and 11,500 cycles. A witness near the airport observed the flap separate from the airplane after it crossed the outer marker on final approach to Runway 4. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed dents on the aft end of the left fuel tank, and dents and a hole to the engine cowling. The inboard and outboard flap actuator fittings (parts number JW121-8L and JW121-6R) were removed and sent to the Office of Research and Engineering, Materials Laboratory Division in Washington, D.C. for examination. The flap actuator fittings were examined at the NTSB Office of Research and Engineering, Materials Laboratory Division on July 16, 2004. Examination of the inboard flap actuator fitting revealed two separate regions of fatigue fractures on both sides of a manufactured hole. Each fatigue region displayed two areas with different types of fatigue cracking characteristics. Approximately one half of each fatigue region close to the origin area displayed a river pattern that radiated out from the fatigue origin areas near the corner between the hole and exterior surface. The remainder of the fatigue regions displayed a distinct banded appearance, consistent with rapid crack propagation and high stress fatigue cracking in aluminum alloys. The areas outside of the fatigue regions were consistent with overload. Areas of pitting and exfoliation, consistent with corrosion, were observed on the surface of the inboard fitting below the areas of the fatigue fractures. The outboard actuator fitting displayed fractures consistent with overload with no evidence of fatigue.