One of Joby Aviation’s pre-production prototypes broke up mid-flight after losing a propeller blade during envelope-pushing flight-testing in February 2022.
That is according to a 7 February accident report released by the US National Transportation Safety Board (NTSB), which includes new information about the previously disclosed crash.
In response to the report, Joby says the accident prompted it to adopt ”a range of improvements to our design and testing methodologies, many of which were already planned”.
On 16 February 2022, Santa Cruz-based Joby was conducting a remotedly operated flight-test programme with one of its electric vertical take-off and landing (eVTOL) aircraft, during which the vehicle was pushed beyond its anticipated operating conditions.
After taking off vertically, transtioning to forward flight and climbing to 11,000ft, the aircraft – which is planned to travel at a top speed of 178kt (330km/h) – was sent into a dive.
”After reaching a maximum dive speed of 181kt indicated airspeed at an altitude of approximately 8,900 ft, a propeller blade… experienced a bending failure near the root of the blade, which culminated in the release of the propeller blade,” the NTSB finds.
The blade’s detachment resulted in “cascading effects to include the separation of multiple motor/propeller assemblies and the loss of remote pilot control of the aircraft”, the agency says. Four more blades detached from the same propeller before the aircraft hit the ground.
Joby’s prototype crashed in an uninhabited area near Jolon, California – a rural area about 174mi (280km) south of San Francisco. “There were no injuries, and the aircraft was destroyed”, according to the NTSB.
Several battery pack structures failed during the impact, causing two fires “largely confined to battery cells that were damaged” in the crash. The fires were extinguished by responders.
The NTSB determines that the propeller blade’s separation was caused by “an anomalous propeller tilt system condition” as well as ”unanticipated aerodynamic interactions” caused by the dive manoeuvre.
Destroyed in the accident was one of two second-generation, pre-production prototypes constructed by Joby. It was all-electric and fly-by-wire, and had logged nearly 96h of flight time.
The company’s second pre-production prototype has flown nearly 22,000nm (40,235km), including more than 100 flights with a pilot on board, Joby says.
”Experimental flight test programmes are intentionally designed to determine the limits of aircraft performance and, in doing so, provide critical insight and learnings that support the safe operation of aircraft as well as inform final design elements,” the start-up says.
Joby is planning to launch commercial passenger service with its piloted, four passenger-eVTOL in 2025.