"Autopilot software has incredibly high profit margins which makes it critical to Tesla's shot at overall profitability," said Edward Niedermeyer, the author of an upcoming book on Tesla.

The latest crash occurred in Delray Beach, Florida, and involved a Model 3. The accident was at least the third of its kind in the U.S. and raises concerns about Tesla's Autopilot technology. Tesla's manufacturing operation burns so much cash that the company's long-term path to generating profits relies on its software.

Elon Musk , Tesla's billionaire co-founder and CEO, has been touting the company's self-driving technology, going so far as to say last month that it will have 1 million robotaxis on the road next year. While investors are used to discounting Musk's public comments because of how frequently the company has failed to deliver on its promises, actual reports of safety hazards create a deeper problem.

Tesla shares fell almost 8% on Friday to their lowest close since December 2016, after the National Transportation Safety Board said the company's Autopilot driver assistance system was engaged during a fatal crash in March.

The NTSB said that on March 1, a Model 3 struck a truck tractor connected to a semitrailer. The Tesla's roof "was sheared off as the vehicle underrode the semitrailer" and the car's 50-year-old driver died in the crash.

"Preliminary data from the vehicle show that the Tesla's Autopilot system — an advanced driver assistance system (ADAS) that provides both longitudinal and lateral control over vehicle motion — was active at the time of the crash," the report said. "The driver engaged the Autopilot about 10 seconds before the collision. From less than 8 seconds before the crash to the time of impact, the vehicle did not detect the driver's hands on the steering wheel."

In an emailed statement, a Tesla spokesperson said its vehicle logs from the crashed car indicated that the driver first engaged Autopilot 10 seconds before the accident and then "immediately removed his hands from the wheel," adding that "we are deeply saddened by this accident and our thoughts are with everyone affected by this tragedy." Tesla said it informed the proper authorities about that detail shortly after the crash.

"Our data shows that, when used properly by an attentive driver who is prepared to take control at all times, drivers supported by Autopilot are safer than those operating without assistance," the company said.

Tesla's stock has been on a steady decline since late last year because of a lawsuit for fraud filed by the Securities and Exchange Commission, announced job cuts and the company's deteriorating cash position. At its current price of about $211, the stock is worth a little more than half of the $420 that Musk said in August investors were willing to pay to take the company private in his notorious "funding secured" tweet.

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