On August 16, 2010, about 1150 mountain daylight time, an experimental Clark RV-6A, N621AL, nosed over onto its back alongside the runway at Nampa Municipal Airport, Nampa, Idaho. The private pilot, who was the sole occupant, received fatal injuries, and the airplane, which was owned and operated by the pilot, sustained substantial damage. The 14 Code of Federal Regulations Part 91 high-speed taxi test was being conducted in visual meteorological conditions. No flight plan had been filed. According to Federal Aviation Administration (FAA) records, the recently completed amateur-built experimental airplane, which was equipped with a fully-castoring nosewheel, received its airworthiness certificate on August 11, 2010 (five days prior to the accident). According to witnesses who had talked with the pilot, he was planning on making his first flight in that airplane on the afternoon of August 16, and in preparation for that flight, he was performing a series of high-speed taxi test runs. During the first taxi test run, the airplane was seen proceeding west on runaway 29 at a groundspeed that was estimated to be between 40 to 60 knots. Witnesses noticed that the airplane developed a significant nose wheel shimmy as it reached a point about two-thirds of the way down the runway. At that point, according to the witnesses, the pilot began rising and lowering the nose of the airplane a slight amount, and they assumed that he was doing so in order to try to reduce the shimmy. Soon thereafter, the pilot slowed the airplane near the west end of runway 29 and then reversed course so he could do another high-speed taxi test to the east on runway 11. As the airplane accelerated to a speed of about 50 knots, witnesses observed a "significant" nose wheel shimmy reoccur. Then, once again, witnesses saw the airplane's nose rise slightly, which they assumed was the pilot's attempt to reduce the shimmy. This was followed almost immediately by the airplane becoming airborne to a height of three to five feet above the runway surface. Almost immediately after it became airborne, the airplane's nose lowered, and the nose wheel struck the runway surface, followed immediately by runway contact by the airplane's main landing gear. This contact initiated what was described as a "porpoising sequence" whereupon the nose wheel struck the runway immediately prior to the main gear striking the runway a series of three times. On the third time, the nose wheel impacted the runway surface with sufficient force as to result in the collapse of the nose gear strut, whereupon the airplane slid along the runway surface on its lower nose cowl. At that point, the main landing gear tires began to skid in a manner consistent with the pilot applying both main gear brakes. Soon thereafter, the airplane departed the right side of the runway, and after encountering the adjacent soft terrain, it nosed over onto its back. When witnesses arrived at the airplane, they found that the canopy had been crushed upward into the cockpit area, and the pilot had suffered, "...significant head trauma." Although the pilot was still alive when taken from the scene by emergency medical personnel, later at the hospital he succumbed to the head injuries he had received during the accident sequence. An autopsy conducted by the Canyon County Coroner's Office determined that cause of death was, "Skull fractures with acute subarachnoid hemorrhage due to blunt trauma to the head." The same autopsy determined that the manner of death was "Accidental." The autopsy also determined that the pilot had moderate coronary artery disease, but no evidence of acute or chronic ischemia (heart attack) was observed. In addition, the autopsy report noted evidence of resuscitation attempts, indicating in part that "... There were IV's in both arms ...." The FAA's Bioaeronautical Science Research Laboratory performed a forensic toxicology examination on specimens taken from the pilot, and that examination was negative for carbon monoxide and cyanide in the blood, and negative for ethanol in the urine. The toxicology report listed the following positive findings: 63.13 (ug/ml, ug/g) Acetaminophen detected in the urine. Chlorpheniramine detected in the urine. Chlorpheniramine NOT detected in the blood (heart). 0.023 ug/ml, ug/g) Diphenhydramine detected in the blood (heart). Diphenhydramine detected in the urine. Omeprazole detected in the blood (heart). A review of the pilot's FAA medical records revealed that the pilot had noted a history of "frequent or severe headaches" on applications for airman medical certificates since 1995. On an application for a third class airman medical certificate on June 25, 2007, under "Comments on History and Findings" was noted "Airman reports two types of headache: occasionally will have ‘sinus' headache which is relieved with Excedrin [acetaminophen/aspirin/caffeine] or Sine-off [acetaminophen/chlorpheniramine/phenylephrine] sometimes last several days, not disabling. Three or four times per year will have migraine preceded by aura of wavy lines followed by severe headache in 30-60 minutes. Also takes Excedrin. If flying when this occurs, would need to turn over to his wife who is a pilot. ... will obtain neurologist evaluation and forward for review." A neurology evaluation dated June 26, 2007, noted in part that the pilot "... finds that if he takes Excedrin that he can abort his headache, otherwise they will last 2 or 3 hours. ... stable migraine problem ... Given his flight physical, would consider screening testing to exclude alternate etiologies including MR imaging and EEG." An internal electronic FAA memorandum dated August 6, 2007, noted "Airman has reported headaches for years, on no prescription meds for this, sending eligibility letter with warning." There was no documentation that the FAA requested any further information from the pilot. An inspection of the airplane's nose wheel support structure and steering system by the FAA Inspector who responded to the scene did not reveal any anomaly in the support system, or any reason for the development of the nose wheel shimmy.