Amateur-built THORP T-18 accident near Tehachapi, California, June 20, 2011

The NTSB's narrative final · quoted from the NTSB record

The pilot was making an approximate 40-minute flight to his home airport during daylight visual meteorological conditions. After he did not check in at his expected arrival time, his family reported him overdue. The wreckage was subsequently located by a local resident after he observed debris on a road, looked over the edge of a mountain, and saw the accident site. Radar data showed the airplane traversing a mountain range in a straight-and-level flightpath, entering an adjoining valley, and then entering a descent of between 700 and 900 ft per minute. The last radar return was about 15 miles from the accident site, which was located about 200 ft below the ridgeline on the west-facing side of the 4,400-ft-tall mountain. The airplane impacted the rising terrain in a wings-level attitude. Postaccident examination of the airframe and engine revealed no mechanical anomalies that would have precluded normal operation. About 6 months before the accident, the pilot and his wife reported a significant change in the pilot's behavior to the pilot's endocrinologist, who prescribed further medical evaluation and consultation; however, no records of any further evaluation or consultation were found. Postmortem toxicology tests on the pilot identified donepezil, which is used to slow the progression of dementia in Alzheimer's disease. The medication does not carry a specific warning, but it has been associated with fainting, dizziness, and other neurological symptoms in some patients. Although it could not be determined whether the pilot was impaired by the effects of donepezil at the time of the accident and the exact extent of the pilot's cognitive decline could not be determined, it is likely that he was cognitively impaired and, thus, at an increased risk for an accident. The pilot also had other chronic medical problems, including diabetes, hypertension, and high cholesterol. Further, the pilot's autopsy revealed that he had moderate-to-severe coronary artery disease and biventricular hypertrophy, which placed him at risk for impairment or incapacitation from a cardiac event such as acute ischemia or arrhythmia that would not be evident during an autopsy. Thus, he may have been impaired or incapacitated at the time of the accident as a result of his extensive heart disease. Postmortem toxicology testing on the pilot also detected metoprolol (a beta blocker used to treat high blood pressure and control heart rate); however, it is not likely that it impaired the pilot. Further, the testing detected therapeutic levels of the antihistamine doxylamine, which due to its significant sedating effects is also marketed as an over-the-counter sleep aid and carries the warning that, at therapeutic levels, it "may impair mental and/or physical ability required for the performance of potentially hazardous tasks (e.g., driving, operating heavy machinery)." It is likely that the pilot was impaired by doxylamine at the time of the accident.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.