The agency found no evidence that the vehicle's crash-avoidance systems kicked in before the horrific crash, which sheared off the front-end of the Model X and killed its 38-year-old driver, Apple engineer Wei 'Walter' Huang.
"At three seconds prior to the crash and up to the time of impact with the crash attenuator, the Tesla's speed increased from 62 to 70.8mph, with no precrash braking or evasive steering movement detected," the report notes.
Huang was traveling along a section of US Highway 101 in Mountain View on March 23 when his vehicle crashed into a road barrier dividing the main highway and an exit ramp.
After impact, the vehicle was hit from the rear by two other vehicles and subsequently burst into flames due to damage to the lithium-ion battery caused by the collision.
Bystanders dragged Huang alive from the vehicle before it was engulfed in flames, and he was transported to a local hospital where he died from his injuries.
According to NTSB, the Tesla crashed at 71mph in a section of road with a speed limit of 65mph. The agency describes a curious sequence of actions by the Tesla's Autopilot in the seconds leading up to the crash.
The NTSB found that Huang's hands touched the steering wheel on three occasions for a total of 34 seconds during the final 60 seconds before the crash, but his hands didn't touch the wheel once in the last six seconds.
The Tesla's 'traffic-aware' cruise control was set to 75mph at the time of the crash and Autopilot was engaged continuously for the 18 minutes leading up to it.
The traffic-aware feature allows the driver to set a speed as well as a fixed distance from a vehicle in front.
At eight seconds before the crash, the Tesla was following a lead vehicle and traveling at the 65mph speed limit. A second later the Tesla began veering left though it was still trailing the lead vehicle.
However, at four seconds before the crash, the Tesla stopped following the vehicle, began accelerating and was headed towards the barrier that it smashed into at 71mph.
NTSB acknowledges that the barrier's built-in crash attenuator, which is designed to adsorb the impact of a crash, had been damaged a week earlier by another crash. It made no comment about the precise condition of attenuator or whether it influenced the outcome.
Tesla however has previously issued a statement blaming the extent of damage to the vehicle on the damaged crash attenuator.
"The reason this crash was so severe is because the crash attenuator, a highway safety barrier which is designed to reduce the impact into a concrete lane divider, had been crushed in a prior accident without being replaced. We have never seen this level of damage to a Model X in any other crash."
The agency also notes that after the fire had been extinguished and the Tesla taken to a pound, its battery started smoking and hissing that afternoon. Five days later the battery reignited and was extinguished by the local fire department.
The NTSB is still working with the California Highway Patrol and the California Department of Transportation to collect "all pertinent information relating to the vehicle operations and roadway configuration".
"All aspects of the crash remain under investigation as the NTSB determines the probable cause, with the intent of issuing safety recommendations to prevent similar crashes," the NTSB notes.