On September 18, 1998, about 1800 hours mountain standard time, an experimental Aero Vodochody L-39 (single engine imported jet trainer), N44529, landed short of the runway and struck a localizer antenna at the Williams Gateway Airport, Mesa, Arizona. The aircraft sustained substantial damage and there was damage to the antenna. Neither pilot was injured. The aircraft was being operated under the provisions of 14 CFR Part 91 by Advanced Training Systems International, Inc., Higley, Arizona, in preparation for work on a U.S. government contract. The local flight had begun about 1700 and was terminating at the time of the accident. Visual meteorological conditions prevailed and no flight plan was filed. The first pilot was a commercial airplane rated pilot and the second pilot was an airline transport rated pilot. The first pilot reported that he had 20 hours in the L-39 and was flying as pilot-in-command (PIC) and safety pilot in the rear seat of the aircraft. He held a Letter of Operational Authority (LOA) issued by the Federal Aviation Administration (FAA), which authorized him to act as PIC in the L-39. The second pilot was in the front seat, flying his first flight in the L-39. The PIC reported that after practicing standard maneuvers, they returned to the airport to conduct pattern work. After the first touch-and-go landing, they climbed to 3,000 feet to prepare for a simulated flame out (SFO) approach to runway 30C. He reported that the second pilot configured the aircraft with the landing gear down, full flaps at 44 degrees, speed brakes out, and power set at 70 percent. He stated that about 300 feet agl, the second pilot realized he was a little slow so he decided to go around. The second pilot moved the throttle full forward and retracted the speed brakes. The PIC stated that "the engine did not seem to respond properly and we were not arresting our sink rate." He further stated that the engine "didn't quit, but didn't seem to produce any additional thrust." About "10 to 12 seconds" later the aircraft landed hard 700 feet short of the runway in the asphalt over-run area. After touchdown, the aircraft veered about 15 degrees to the right and off the runway. The second pilot got the airplane airborne again, but only for a few hundred yards. The PIC stated that they touched down again in the dirt and at that point he took the controls. He reported that he intended to return to the runway, but the aircraft struck the localizer antenna with the right wing tip, which he had not been able to see from the back seat. The PIC reported that he attempted to maintain a level attitude and stop the aircraft. About 150 yards before the airplane came to a stop, the second pilot ejected from the aircraft without warning. The aircraft came to a rest in an upright attitude in the desert brush. The PIC stated that he hadn't experienced any problems with the engine prior to the accident. The pilot's operating handbook for the accident aircraft was reviewed and relevant portions are appended to this file. The handbook indicated that the pilot should decide whether to continue the landing or eject while at a decision height of 800 feet agl. The handbook further indicated that the spool-up time for the aircraft engine was 9 to 12 seconds. In two interviews with the Safety Board, the PIC stated that he expected the engine to spool up in "4 to 5 seconds." The aircraft owner reported that he saw the accident aircraft immediately following the accident and noted the flaps to be in the takeoff position of 25 degrees. He further stated that the PIC reported that during the descent, it felt as if "the bottom fell out." Post-crash examination of the aircraft by the Safety Board revealed that the flaps were at 25 degrees down. In an interview with the Safety Board investigator, the pilot reported that he thought the flaps were still full down at the time of impact. Following the accident, an L-39 flight instructor simulated the circumstances of the accident. He climbed to about 5,000 feet, added full power from an idle position, and brought the flaps up from the full down position to the takeoff position. He reported that the aircraft immediately sank about 600 feet. The flight instructor reported that it has always been his experience that raising the flaps before establishing a positive rate of climb will cause the aircraft to sink between 500 to 700 feet per minute.