The National Transportation Safety Board (NTSB) said earlier this month the two engines of the helicopter that crashed in hazy, cloudy weather on a California hillside last month showed no evidence of a "catastrophic internal failure,"
The interim report said examination of both rotor assemblies found damage "consistent with powered rotation at the time of impact."
The findings, while preliminary, pointed to no obvious signs of mechanical problems that may have contributed to the fiery crash.
NTSB board member Jennifer Homendy said in January that clouds, fog and limited visibility reported in the vicinity of the crash would be a key focus of the investigation.
Zobayan, an experienced aviator certified as an instructor, was navigating by visual orientation, not by instrument guidance, during the entirety of the ill-fated flight, the NTSB said.