Federal agency probing Tesla's Autopilot feature after fatal crash

The National Highway Traffic Safety Administration (NHTSA) has opened a preliminary investigation into the performance of Tesla's Autopilot feature during a fatal crash that occurred last month.

The autopilot feature was engaged when the driver of a 2015 Model S was killed in a May 7 accident in Williston, Florida, according to the NHTSA. The incident "calls for an examination of the design and performance of any driving aids in use at the time of the crash," the agency said.

Such an investigation is the first step the NHTSA would take before ordering a recall if necessary. The evaluation "should not be construed as a finding that the Office of Defects Investigation believes there is either a presence or absence of a defect in the subject vehicles," NHTSA Communications Director Bryan Thomas said in a statement.

Tesla reported the incident to the NHTSA, and the agency deployed its Special Crash Investigations Team to investigate the vehicle and crash scene.

Tesla learned about the preliminary Autopilot investigation on Wednesday evening, the company said in a blog post.

Here's what Tesla has to say about the incident:

What we know is that the vehicle was on a divided highway with Autopilot engaged when a tractor trailer drove across the highway perpendicular to the Model S. Neither Autopilot nor the driver noticed the white side of the tractor trailer against a brightly lit sky, so the brake was not applied. The high ride height of the trailer combined with its positioning across the road and the extremely rare circumstances of the impact caused the Model S to pass under the trailer, with the bottom of the trailer impacting the windshield of the Model S. Had the Model S impacted the front or rear of the trailer, even at high speed, its advanced crash safety system would likely have prevented serious injury as it has in numerous other similar incidents.

Tesla defended its autonomous driving technology, noting that this is the first known fatality linked to Autopilot, after more than 130 million miles have been logged with the feature activated. By comparison, there is a fatality for every 94 million miles driven among all vehicles in the U.S.

"As more real-world miles accumulate and the software logic accounts for increasingly rare events, the probability of injury will keep decreasing," Tesla said. "Autopilot is getting better all the time, but it is not perfect and still requires the driver to remain alert."

Tesla noted that when activated, the Autopilot feature alerts drivers that they must remain in control. Still, some have criticized the feature as over-hyped. Trent Victor, senior technical leader of crash avoidance at Volvo, recently said that Tesla's Autopilot "gives you the impression that it's doing more than it is." He called the feature "more of an unsupervised wannabe."