Quicksilver Enterprises Inc MXL II N476VB accident near Petaluma, California

Probable cause

The pilot's failure to maintain control of the airplane while maneuvering, which resulted in an uncontrolled descent and structural failure. Contributing to the accident was the pilot's impairment from his use of diphenhydramine.

NTSB analysis

The student pilot was conducting a local area flight in daytime visual meteorological conditions. Multiple witnesses located near the accident site reported observing the airplane maneuvering over the area. Two witnesses reported seeing the airplane in a steep descent with the wings folded upward before it impacted the ground.

Postaccident examination of the accident site and the airplane revealed signatures consistent with a high-speed, near-vertical impact with terrain. No evidence was found of any preexisting mechanical anomalies that would have precluded normal operation of the airplane.

It's likely that while maneuvering, the pilot lost control of the airplane, which resulted in a steep descent from which the pilot did not recover. During the vertical descent, the airplane's structural capabilities were exceeded, and the wing spars failed in overstress. The pilot had applied for a medical certificate in 2003 and 2004: however, he did not provide all the information requested by the Federal Aviation Administration (FAA), and his application was denied. Review of FAA medical records revealed that the pilot had a history of a traumatic brain injury; however, based on a review of the information that the pilot provided in 2004, it is unlikely that the long term effects from the pilot's traumatic brain injury contributed to the accident.

Postaccident toxicology testing identified tetrahydrocannabinol (THC), the psychoactive component in marijuana, in the pilot's blood and various tissues, and diphenhydramine, an over-the-counter allergy and sleep aid medication, in the pilot's blood The levels of THC found in tissues suggested that it was not used recently. Therefore, it is unlikely that the pilot's use of marijuana caused impairment or contributed to the accident. However, the level of diphenhydramine found suggested that, at the time of the accident, the pilot was likely impaired by his use of diphenhydramine.

Text from the NTSB. Open the NTSB docket for WPR15FA140 for the full record.