A man who died after his semi-autonomous Tesla crashed into a concrete barrier was playing a video game on his smartphone at the time of the accident, an investigation has revealed.
Apple engineer Walter Huang died in California in March 2018 while travelling in a Tesla Model X, which was being controlled by the vehicle's partially self-driving Autopilot system.
At a hearing on Tuesday, the National Transportation Safety Board (NTSB) said Huang was playing on his phone and was not alerted by the Tesla's forward collision avoidance system.
"If you own a car with partial automation, you do not own a self-driving car," NTSB Chairman Robert Sumwalt said in his opening statement.
"This means that when driving in the supposed 'self-driving' mode, you cannot read a book, you cannot watch a movie or TV show, you cannot text and you cannot play video games."
Tesla has consistently stated that its current self-driving feature is not fully autonomous, though the NTSB said that more should be done to inform drivers of the technology's limitations.
The American safety regulator also blamed Apple for not "recognising their own responsibility as an employer".
Mr Sumwald said: "They have failed to say of our 135,000 employees, that we care about you. And we don't want you to go out and kill yourself or others on the roadway."
An Apple spokesperson said: "We expect our employees to follow the law."
Documents previously released by the NTSB revealed that Huang had complained about the Tesla's Autopilot system on the same stretch of Silicon Valley motorway where the fatal crash occurred.
Huang told his wife that his Model X had veered towards the barrier on his commute to work, according to a statement from the Huang's family lawyer.
Despite not being fully self-driving, Tesla claims its Autopilot feature is up to nine-times safer than human drivers. During its third quarterly update last year, the electric car maker published safety figures that appeared to support this.
"During Q3, we registered one accident for every 4.34 million muiles driven in which drivers had Autopilot engaged," the update stated.
"This compares to the national average of one accident for every 0.5 million miles based on NHTSA's most recent data."
A 2019 survey by Bloomberg of 5,000 Tesla owners found that 90 per cent of drivers felt the Autopilot feature made them safer.
Earlier this month, two Tesla owners in Dorset credited their Model X vehicles for saving their lives after the Autopilot feature automatically applied the brakes to prevent the cars from hitting the same falling tree.