A McDonnell Douglas Aerospace (MDA) pilot was flying a leased Navy F/A-18C and conducting an airshow practice at St. Louis Regional Airport when the airplane impacted the ground at the bottom of a reverse one-half Cuban eight aerobatic maneuver. The briefed altitude at the top of the maneuver was to be 3,500 feet above ground level (agl), which gave the pilot a base line of 1,000 feet agl. Recorded data showed that the actual altitude at the top of the maneuver was 2,280 feet agl. Using a group of F/A-18 pilots in a F/A-18 simulator, the lowest altitude at the top of the reverse one-half Cuban eight required to successfully complete the maneuver was 2,500 feet agl. The pilot had been trained as a Naval Aviator, and was a graduate of the Navy's test pilot school. He joined MDA Flight Operations 3/4/96. The pilot had accrued 16 hours in the F/A-18 in the last year, of which 11 hours were in the last 90 days. MDA did not have a formal training plan for their pilots who perform airshow demonstration flights. The pilot had flown 5 civilian airshows within the last year; the most recent was 11 days prior to the accident. All the airshows were flown in a Pitts Special.