The NTSB tells us that the chopper came out of Byron and was heading back to its home base at the Silicon Valley Helicopters Shop. The owner of the chopper says the pilot was a very experienced pilot, but we don't know whether the teacher or student was flying it when it crashed.
They went down just after midnight on Sheradin Road off Highway 680, just outside of Fremont. The student was on a required night-flight exercise when this happened. The National Transportation Safety Board says it could take up to a year to determine the probable cause of this fatal chopper crash alongside Interstate 680 near Sunol.
"One of the main causes of helicopter accidents is helicopters flying into high tension lines," says ABC7 News aviation expert Ron Wilson.
One look at the scene leaves no doubt the chopper hit the power lines, spreading them across the freeway.
"Looked to me like he might be having some mechanical problems so I was getting ready to throw the red lights on and shut the freeway down for him if he was going to make an emergency landing. He, in fact, slowed up so slow he actually flew right over me" says witness Larry Anderson.
Fremont Fire Deputy Chief Larry Anderson was on his way home when he saw the chopper flying low and slow. He followed him up the Sunol grade and then to the crash site.
"By the time I got there, it was burning pretty good. It had ignited the vegetation on the hillside. It was so hot, I couldn't' get close enough to help him."
The chopper was a Schweitzer 269. Its owner says the pilot was from Palo Alto. He was a certified flight instructor and the second victim was his student.
Night flight training is required to earn a pilot's license. The FAA says it's unclear who was piloting the chopper at the time of the crash. Conditions were foggy.
Aviation expert Ron Wilson says the pilot should always know the terrain and it is illegal to fly in a fog bank.
"Air traffic and radar can't really determine where he is if the helicopter is at a lower altitude, so he was on his own and unfortunately made a mistake."
The FAA says the pilot was not in communication with air traffic control and that's not uncommon in uncontrolled airspace.
The crash did cause a portion of 680 to close and power was restored. The NTSB says they will have an initial report out within 10 days, but it could take up to a year to determine all the facts regarding this case.