On October 12, 1996, approximately 0624 mountain daylight time, a Keith Vans RV-6A, N16DK, collided with terrain after takeoff from Grassy Meadows Sky Ranch, a private airport south of Hurricane, Utah. The airplane was destroyed and the private pilot (who owned and had built the experimental-category aircraft, according to the FAA's aircraft registry) and a passenger were killed. The airplane was enroute from Grassy Meadows to the Experimental Aircraft Association (EAA) Copperstate Regional Fly-In at Williams Gateway Airport, Phoenix, Arizona. Dark night visual meteorological conditions existed at the time of the accident, and no flight plan had been filed. A witness reported to the Washington County, Utah, sheriff that at approximately 0620, he heard an aircraft performing a run-up in the area of the airport. He then heard an aircraft depart. He stated that at approximately 0622, the aircraft's strobe lights became visible, that the aircraft was departing to the south, and that it was airborne and climbing. He stated that he then walked around to the rear of his property, and that when he looked back toward the airport he could still hear the engine noise but could no longer see the strobes. He stated that at about 0624, he heard a very loud "thud" and that the engine sound ceased at that point. The runway at the Grassy Meadows Sky Ranch is a 4,400-foot-long north-south paved runway. A computer program used by the investigator to determine lighting conditions calculated that morning twilight began at the airport at 0642 that morning (18 minutes after the reported time of the accident), with sunrise at 0739. There was no moon at the time of the accident. The runway is equipped with pilot-controlled medium-intensity runway lights, but information furnished by the president of the Grassy Meadows Sky Ranch Landowners Association indicated that the runway lighting controller sensitivity was degraded at the time of the accident, such that the runway lights could only be activated from a few feet away from the antenna. The September 1996 edition of the landowners association newsletter reported that the runway lights could be turned on manually as needed, if requested by telephone to the airport manager. In a telephone query to the president of the landowners association on March 2, 1998, the landowners association president stated that to the best of his knowledge, the pilot made no such request for the accident flight, and the runway lights were off at the time of the accident. The pilot, who did not hold an instrument rating, had logged a total of 15.2 night hours and 2.8 hours of simulated instrument time. His most recent night experience consisted of 0.9 hours logged on August 28, 1996, and 0.9 hours logged on August 29, 1996. Per these two logbook entries, at the time of the accident the pilot met the recency of experience requirements for night flight specified by 14 CFR 61.57(d). The three next most recent night entries were October 4, 1992 (0.5 hours), October 12, 1995 (0.5 hours), and October 14, 1995 (0.5 hours.) The pilot had last logged simulated instrument time on September 3, 1992, when he had logged 1.5 hours of simulated instrument time on a 1.5-hour night flight in a Cessna 140A. Investigators from the FAA and Textron Lycoming, the engine manufacturer, responded to the accident scene. They reported that the aircraft wreckage was located in rising terrain approximately 1/4 mile west of the south end of the Grassy Meadows runway, and that the main aircraft wreckage was approximately 160 feet west of a pair of ground scars which were 21 feet apart. They reported that they did not find any evidence of pre-impact airframe, systems, or engine malfunction. A photo taken by the FAA investigator showed the aircraft's vertical speed indicator needle captured at a 1,900 foot per minute descent rate indication. Fuel was found on board the aircraft. Toxicology tests conducted on the pilot by the FAA Civil Aeromedical Institute (CAMI), Oklahoma City, Oklahoma, detected 0.094 ug/ml of diphenhydramine (trade name Benadryl) in the pilot's blood, 0.152 ug/ml of diphenhydramine in the pilot's liver fluid, and 33.400 ug/ml of acetaminophen (trade name Tylenol) in the pilot's lung fluid. According to the Physician's Desk Reference (PDR), 44th Edition (1990), diphenhydramine is an antihistamine with anticholinergic (drying) and sedative effects. Indications and usage of the drug are listed as antihistaminic, motion sickness, and antiparkinsonism. Warnings regarding use of the drug include: "Patients...should be advised that this drug may cause drowsiness....Patients should be warned about engaging in activities requiring mental alertness such as driving a car or operating appliances, machinery, etc." The most frequent adverse reactions of the drug listed in the PDR include sedation, sleepiness, dizziness, and disturbed coordination.