The National Transportation Safety Board has released its preliminary findings about a deadly crash of an experimental helicopter earlier this month northeast of Phoenix.
However, an exact cause of the April 16 crash wasn't revealed in the NTSB report released Thursday.
Pilot and Embry Riddle Aeronautical University Professor Rucie Moore and an engineering manager both died when the Bell 206B experimental helicopter went down in an alfalfa field on the Fort McDowell Indian Reservation.
A witness reported hearing a loud bang and seeing the helicopter fall from the sky.
The NTSB report says the purpose of the flight was to evaluate developmental rotor blades that had been installed on the helicopter.
The aircraft was on the second leg of a test flight that was scheduled to be the last test for the rotor blades.