When a Tesla Model X slammed into a concrete highway barrier in California last month, the vehicle's computers contained a wealth of information about the moments leading to the fatal accident.
The problem for U.S. accident investigators is that the information wasn't easily accessible. The data stored on the Tesla is in a proprietary format that can only be accessed by the company. Similarly, the information the vehicles beam to Tesla computers on a regular basis can't be obtained without the company's cooperation.
"It makes a challenging investigation more so," said Peter Goelz, a former managing director at the National Transportation Safety Board who is now senior vice president at O'Neill & Associates, a Washington lobbying and public relations firm.
Unlike the trove of information contained on an airplane's crash-proof recorders -- the "black boxes" that capture flight data and sounds from the cockpit in an easy-access format -- the NTSB needs the help of automakers such as Tesla to view the information from the growing number of autonomous and semi-autonomous vehicles.
That requires a cooperative relationship that appears tested by the latest accident, on March 23. While the agency says Tesla has been responsive, the company's decision Friday to release information on the investigation without NTSB's permission and a Monday afternoon Twitter jab against the safety board by CEO Elon Musk has heightened tensions.
Musk defended his company's decision to release the information. "Lot of respect for NTSB," he said on Twitter, adding: "Tesla releases critical crash data affecting public safety immediately & always will. To do otherwise would be unsafe."
The release of data by an official participant in an NTSB inquiry is prohibited by law and agreements that parties to an investigation must sign. It's also highly unusual for a participant to be critical of the NTSB during an open investigation.