Airborne XT 912 N670EM accident near Hawthorne, California

Probable cause

The weight shift control aircraft encounter with a wake vortex from a preceding airplane, which resulted in a roll upset at an altitude too low for recovery. Contributing to the accident was the accident pilot's failure to recognize the potential for a wake vortex encounter.

NTSB analysis

The student pilot of the weight shift control (WSC) light sport aircraft, commonly referred to as a "trike," advised the air traffic control (ATC) tower that she was ready for departure and was instructed to hold short. A DeHavilland DHC-6 then landed, and, about 40 seconds later, the controller cleared the trike for departure on the same runway. When the trike was about 50 ft above ground level, it entered a steep right bank and descended to ground impact just north of the east-west runway. Postaccident examination of the airframe and engine did not reveal evidence of any pre-impact anomalies. Trajectory comparisons of the two aircraft, revealed that the trike likely encountered one of the wingtip vortices from the DHC-6, and the strength of that vortex, depending on the encounter geometry, likely far exceeded the roll authority of the trike. This resulted in an airborne loss of control at an altitude too low for recovery.

Because the trike and the DHC-6 were of the same ATC weight category, no controller wake vortex advisory was required or issued, and all wake-separation decisions were the responsibility of the pilot. Despite the significant size and weight differences between the 10,500-pound DHC-6 and the 992-pound trike, the pilot opted to depart less than a minute after the DHC-6 landed. Review of the pilot's training syllabus indicated that wake vortices were part of the curriculum, but her actual knowledge and understanding of that subject could not be determined. Her training workbook appeared to be pristine and unused, and the instructor's signoffs appeared to all have been done in a single sitting, possibly even after the accident. This suggested the possibility that her training, academic knowledge, and study diligence left her inadequately prepared to appreciate and avoid the wake vortex hazard.

Although the toxicology results indicated that the pilot had smoked cocaine, it was not possible to determine whether or not the pilot was experiencing any effects from smoking cocaine or from withdrawing from cocaine at the time of the accident. Based on the levels of diphenhydramine found, the pilot may have been impaired by its effects (somnolence, slowed psychomotor responses) at the time of the accident.

Text from the NTSB. Open the NTSB docket for WPR16FA086 for the full record.