LA driver charged over bus collision before fatal news helicopter crash

The driver who slammed her car into an LA bus, killing two people hours before a news helicopter crash, is set to face murder charges.

Bailee Lynn Rios, 36, was under the influence of drugs when she swerved into the wrong lane and ran a red light on Tuesday, prosecutors said.

It was a tragedy compounded by the fatal crash of a TV news helicopter that was covering the collision.

The helicopter, which was used by NBC and Telemundo, crashed about two hours after Ms Rios crashed.

The woman faces two charges of second-degree murder over the deaths of bus passengers Daniel Castillo, 46, and Gage Weida, 31.

"There are no words that can truly capture how much we will miss him or the space he leaves behind in our lives," Mr Castillo's youngest daughter, Johaunna, wrote online.

Ms Rios was being held on $US4.1 million ($5.7 million) bail and is scheduled to appear in court today.

The mother of the accused said she was shocked and saddened by the string of events.

Cindy Rios said she had not spoken to her daughter since her arrest and had not been contacted by law enforcement.

The final moments of the helicopter crash

The news helicopter crash killed both people on board, pilot George Marciniw and reporter Eliana Moreno, and a 29-year-old man on the ground, Edy Gutierrez Mejia.

At least four cars and two storage containers burned after the helicopter caught fire.

There were no immediate details on what caused the helicopter to go down, but investigators said significant clues could come from the last seconds of video the crew broadcast.

In it, an alarm could be heard inside the helicopter's cockpit as it lost altitude.

National Transportation Safety Board investigator Fabian Salazar said the video was "probably the most important evidence that we have discovered so far."

Just after the beeping starts, a woman's voice says, "uh oh."

The helicopter moves quickly away from the bus crash site and starts losing altitude.

The woman says "You can't pull up?" before the video stops as the chopper nears the ground.

Investigations ongoing into helicopter and bus crash

Aviation safety expert Jeff Guzzetti said the alarm suggests a potential loss of engine power and a dangerous decrease in the main rotor speed.

He said the pilot appeared to be trying to perform an emergency manoeuvre to use the wind to force the rotor to spin again.

The NTSB is also investigating the bus collision.

A vigil was planned for Thursday evening to honour the victims of both crashes.

There have been at least eight fatal crashes involving news helicopters in the US since 2000, killing 16 people, according to a review of federal accident records and news accounts.