U.S. auto safety regulators said Thursday they have opened a preliminary investigation into 25,000 Tesla Motors Model S cars after a fatal crash involving its "Autopilot" feature.

The National Highway Traffic Safety Administration said the crash came in a 2015 Model S operating with automated driving engaged, and "calls for an examination of the design and performance of any driving aids in use at the time of the crash." It is the first step before the agency could seek to order a recall if it believed the vehicles were unsafe.



Tesla said Thursday the death was "the first known fatality in just over 130 million miles where Autopilot was activated," while a fatality happens once every 60 million miles worldwide. The electric automaker said it "informed NHTSA about the incident immediately after it occurred."

"It is important to emphasize that the NHTSA action is simply a preliminary evaluation to determine whether the system worked according to expectations," Tesla said in a blog post.

The May crash occurred when a tractor trailer drove across a divided highway, where a Tesla in autopilot mode was driving. The Model S passed under the tractor trailer, and the bottom of the trailer hit the Tesla vehicle's windshield.

"Neither Autopilot nor the driver noticed the white side of the tractor trailer against a brightly lit sky, so the brake was not applied," Tesla wrote.



Tesla noted that customers need to acknowledge that autopilot "is new technology and still in a public beta phase" before they can turn it on. Drivers also acknowledge that "you need to maintain control and responsibility for your vehicle."

Tesla CEO Elon Musk called the death a "tragic loss" in a tweet.

"Our condolences for the tragic loss."

Tesla shares fell about 3 percent in after-hours trading.

— Reuters contributed to this report.