Tesla has presented to the U.S. Senate Commerce Committee two theories about what caused the May 7 fatal crash of a Model S vehicle that was running with the Autopilot system enabled.

At a briefing with congressional aides, Tesla representatives said that the automaker is still investigating the "system failure" that led to the fatality.

The car manufacturer is pointing a finger at the radar and camera input, which might have failed to detect the truck trailer. At the same time, Tesla is looking into whether or not the automatic braking system's radar saw the trailer but mistook it for a piece of road infrastructure, thus "tuning out" the automated braking system.

On May 7, Joshua Brown lost his life when his Model S drove under a tractor-trailer. The incident represents the first time a person was killed while operating a semi-autonomous vehicle. Brown was driving a Tesla Model S, which had its Autopilot system switched on.

Earlier this year, Tesla CEO Elon Musk received a question via Twitter about why the radar failed to detect the truck. Musk replied by pointing out that the detection system "tunes out" objects that it labels as road signs, underlining that this helps the car running at optimal speed and away from "false braking events."

According to Tesla's answers in front of the committee, the carmaker sees braking failures as distinct from its Autopilot feature, which is in charge of changing lanes, steering and tuning travel speed.

The U.S. National Transportation Safety Board (NTSB), for its part, announced the preliminary findings in its own investigation. Data showed that Brown was driving above the legal speed limit, running at 74 mph in a 65 mph zone when it collided with the semi-truck.

In the report, the NTSB also noted that the Model S driver had both the Autosteer lane-keeping assistance and the Traffic-Aware Cruise Control turned on. The NTSB refrained from pinpointing a definitive cause for the crash.

As a reminder, the semi-autonomous system is designed to take control of steering and braking in certain conditions.

The U.S. National Highway Traffic Safety Administration has deployed a separate investigation to determine if the Autopilot system from Tesla's vehicles is actually increasing the safety of drivers.

Tesla claims it to be so, showing that tens of thousands of clients all over the world have banked more than 100 million miles in semi-autonomous driving until the unfortunate accident of Brown.

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