On September 23, 2016, at 1215 eastern daylight time, an Aero Vodochody L39, N139AJ, was substantially damaged after it impacted trees during a runway excursion while landing at Hampton Roads Executive Airport (PVG), Norfolk, Virginia. The private pilot was not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the personal flight that was operated under the provisions of 14 Code of Federal Regulations Part 91.According to the pilot, the airplane was on final approach to runway 28, about 100 ft above ground level and 60 ft from the runway threshold, when there was an "uncommanded" retraction of the flaps. He adjusted the pitch of the airplane and advanced the throttle in order to compensate for the flap retraction. The airplane touched down on the paved surface of the runway, the pilot applied the brakes, and then he applied the emergency brake. As the airplane began to veer toward the side of the runway, the pilot released the emergency brake, and continued to apply the brakes utilizing the brake pedals. The pilot stated that the "normal" braking action was insufficient to keep the airplane from over-running the runway. The airplane continued off the departure end of the runway, struck trees, and came to rest about 1,050 feet from the end of runway 28, which was a 5,350-ft-long runway. An examination of the runway revealed that skid marks from the airplane began around 1,000 ft prior to the departure end of the runway and continued into the area where the airplane came to rest. According to Federal Aviation Administration (FAA) records, the airplane was issued an experimental exhibition airworthiness certificate on December 12, 2007. It was powered by a Ivchenko, AI-25TL engine. According to the pilot, the most recent condition inspection was performed on September 1, 2016, at an airframe total time of 3,016.9 total hours. According to the emergency checklist located in the airplane, it was equipped with an emergency flap extension system. The pilot did not mention using the emergency flap extension system during the accident sequence. An examination of the flap system, under the oversight of an FAA inspector, revealed that there were no disconnects or abnormalities in the flap mechanical actuation system besides the impact damage, which prevented a test of the flap system. The flap actuator was intact and no evidence of hydraulic leakage was noted. The emergency flap extension handle located to the right of the pilot's seat was moved without anomaly. A review of the accident airplane's flight manual revealed, under the conditions that existed at the time of the accident, that the landing ground roll distance was approximately 2,000 feet, and was based on the circumstances of idle engine power, full flaps, and the speedbrakes retracted.