(Bloomberg) -- The U.S. National HighwayTraffic Safety Administration has opened an investigation intoa fatal accident involving a Tesla MotorsInc. sedan when the electric-auto maker’s Autopilot softwarewas engaged.

The incident, which occurred on May 7 in Williston, Florida, wasreported to NHTSA by Tesla. Shares in the automaker fell 2.7% to$206.50 at 4:50 p.m. New York time after closing regular trading up1% at $212.28.

Extremely rare circumstance

Tesla has always prided itself on its safety record. In August2013, the Model S sedan was awarded a 5-star safety rating byNHTSA. The company’s website states that “Model S comes withAutopilot capabilities designed to make your highway driving notonly safer, but stress free.”

In a blog post published Thursday, Tesla said that the fatalcrash is the first known fatality in more than 130 million miles ofAutopilot driving.

“What we know is that the vehicle was on a divided highway withAutopilot engaged when a tractor trailer drove across the highwayperpendicular to the Model S,” Tesla said in the post.“Neither Autopilot nor the driver noticed the white side of thetractor trailer against a brightly lit sky, so the brake was notapplied. The high ride height of the trailer combined with itspositioning across the road and the extremely rare circumstances ofthe impact caused the Model S to pass under the trailer, with thebottom of the trailer impacting the windshield of the Model S.”

‘Beyond saddened’

Tesla said that the “customer who died in this crash had a lovingfamily and we are beyond saddened by their loss. He was a friend toTesla and the broader EV community, a person who spent his lifefocused on innovation and the promise of technology and whobelieved strongly in Tesla’s mission. We would like to extend ourdeepest sympathies to his family and friends.”

Tesla began rolling out its Autopilot features in October.Autopilot is a step toward autonomous or self-driving cars, andincludes features like automatic lane changing, auto steering andthe ability of the vehicle to parallel park itself. In releasenotes about the software updates that are sent to owners, Teslastresses that drivers still maintain responsibility for safedriving and should keep their hands on the wheel at all times.

“Similar to the autopilot functions in airplanes, you need tomaintain control and responsibility of your vehicle while enjoyingthe convenience of Autopilot in Model S,” Tesla has said.

Related: Driverless cars: What are the insuranceimplications?

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