On March 7, 2005, approximately 0830 central standard time, an Aero Vodochody L-39C experimental military jet trainer, N8098T, registered to and operated by the pilot, was substantially damaged during a runway overrun while landing on Runway 14 at the Shreveport Downtown Airport (DTN), near Shreveport, Louisiana. The airline transport pilot and passenger received minor injuries. Instrument meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the 14 Code of Federal Regulations Part 91 personal flight. The 238-nautical mile cross-country flight originated from the Houma-Terrebonne Airport (HUM), near Houma, Louisiana, approximately 0730, and was destined for DTN. The 7,200-hour pilot reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that during a non-precision instrument approach to runway 14, at an airspeed of 140 knots, "the airplane experienced a downdraft causing the airplane to sink to 500 feet" mean sea level (msl), however, the pilot corrected the altitude and leveled off at 700 feet msl. After descending to the minimum descent altitude of 600 feet msl, the pilot saw the runway environment and continued the approach. At this time he noted light rain showers in the area. The pilot stated that after selecting full flaps and verifying the landing gear was down and locked, he performed a "normal landing in the normal touchdown area of runway 14." During the landing roll, he noted that braking action was "poor" and "the runway seemed wavy." The pilot then applied maximum braking using the hand brake while moving the control stick forward "to depress the squat switch on the nose wheel for braking," however, braking action remained poor. The pilot added that due to the 10-second spool-up time from idle power to full power, a go-around was not an option, and he elected to pull the emergency brake handle to assist in stopping the airplane. Subsequently, at an airspeed of approximately 20 knots, the airplane exited the departure end of runway 14, rolled down a shallow hill, and came to rest in a nose low attitude near an airport service road. A witness located on the ramp area of the airport reported in a written statement that he observed the L-39 during the landing roll on runway 14 near the runway 23/5 intersection "traveling quite rapidly." Using the Landing Ground Roll calculation chart (Figure A7-3-TAB) within the operating handbook for the L-39, the pilot calculated that the required landing distance for the estimated landing weight and speed to be approximately 2,612 feet. The chart states that the following conditions must exist: Idle power setting, full flaps, and speed brakes retracted. The pilot stated in the NTSB Form 6120.1/2 under the Recommendation (How This Accident Could Have Been Prevented) section: "more conservative estimation of runway stopping distance on [a] wet runway and better airspeed control on short final after viewing the runway environment." Runway 14 is a 5,018-foot long and 150-foot wide asphalt runway. The airport manager reported the runway features slight upslope mid-length to assist in water draining. Examination of the runway by airport personnel shortly after the accident revealed no pooling of water; however, the surface of the runway was wet. Examination of the airplane, by the pilot revealed the nose structure was crushed downwards and aft. The nose wheel landing gear was also collapsed and pushed aft. At 0753, the automated surface observing system at DTN reported wind from 250 degrees at 3 knots, visibility 2 statute miles, rain, cloud condition overcast at 600 feet, temperature 15 degrees Celsius, dew point 13 degrees Celsius, and an altimeter setting 29.85 inches of Mercury. At 0853, the automated surface observing system at DTN reported wind from 250 degrees at 4 knots, visibility 1 statute mile, rain, cloud condition broken at 400 feet, broken at 1,000 feet, and overcast at 1,700 feet, temperature 16 degrees Celsius, dew point 14 degrees Celsius, and an altimeter setting of 29.86 inches of Mercury.