In a letter to the automaker’s founder Elon Musk, NTSB Chair Jennifer Homendy questioned Musk's decision to allow drivers access to his firm’s “Full Self-Driving Beta technology” without having first rectified the problems with the system that have caused multiple fatal crashes in recent years.

The NTSB is still investigating the most recent fatal accident, which occurred in April this year, and which killed both occupants of the vehicle.

The driver's Tesla car reportedly crashed after losing control while trying to take a curve at high speed. Neither the driver nor his fellow passenger was at the wheel, ready to take control in the event of an incident, as is required under the terms of Tesla’s driverless software. However, Tesla's vehicles have no system in place to ensure that drivers are using the functionality as intended.

“If you are serious about putting safety front and centre in Tesla vehicle design, I invite you to complete action...