(Adds details of crash, prior NTSB probes)
By David Shepardson
March 27 (Reuters) - The U.S. National Transportation Safety Board is opening a field investigation of a fatal Tesla Inc crash and major vehicle fire near Mountain View, California, last week, the agency said in a statement on Tuesday.
It was unclear if the car was being driven by its automated control system at the time of the accident, which killed the Tesla driver and involved two other cars, the NTSB said in a Twitter post. Tesla vehicles have a system called Autopilot that handles some driving tasks at times.
Tesla did not immediately comment.
The California Highway Patrol said the electric-powered Tesla Model X crashed into a freeway divider on Friday and then was hit by a Mazda before colliding with an Audi. The Tesla's lithium batteries caught fire and emergency officials consulted Tesla engineers advice before determining it was safe to move the vehicle and how to extinguish the battery fire. NTSB said the issues being examined include the post-crash fire and removing it from the scene.
In January, the NTSB and U.S. National Highway Traffic Safety Administration sent investigators to California to investigate the crash of a fire truck and a Tesla that apparently was traveling in semi-autonomous mode.
The NTSB can make safety recommendations but only NHTSA can order automakers to recall unsafe vehicles or fine automakers if they fail to remedy safety defects in a timely fashion. Before the agency could demand a recall from Tesla, it must open a formal investigation, a step it has not yet taken. Tesla's Autopilot allows drivers under certain conditions to take their hands off the wheel for extended periods. Tesla requires users to agree to keep their hands on the wheel "at all times" before they can use Autopilot.
The NTSB faulted Tesla in a prior fatal Autopilot crash.
In September, NTSB Chairman Robert Sumwalt said operational limitations in the Tesla Model S played a major role in a May 2016 crash in Florida that killed a driver using Autopilot. That crash raised questions about the safety of systems that can perform driving tasks for long stretches with little or no human intervention but cannot completely replace human drivers.
Tesla in September 2016 unveiled improvements to Autopilot, adding new limits on hands-off driving. (Reporting by David Shepardson Editing by Susan Thomas and Bill Trott)