One prototype air taxi suffered a software glitch, lost control and nosed into a field. Another’s computer erroneously thought it was on the ground, shutting off power in flight and plunging it onto the pavement. Batteries on two more burst into flames.

The race to develop a new family of flying machines to whisk people and cargo across traffic-choked cities has drawn billions of dollars of investment and vast promise. But some of the biggest names in aviation have had accidents during testing, according to a Bloomberg review of reports dating back to 2018. They include Boeing and its subsidiary, Aurora Flight Sciences Corp., Textron’s Bell helicopter division, billionaire Larry Page’s Kitty Hawk Corp., Joby Aviation and German air-taxi pioneer Lilium.

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No one has died or been injured, and advocates say accidents are a healthy sign that the industry is pushing the envelope. But the new electric-powered, vertical-takeoff vehicles, or eVTOLs, use innovative technologies that haven’t been tested in routine service, and some safety experts say this means the road to government approval and public acceptance won’t be easy.

The Federal Aviation Administration is preparing to certify a handful of the new aircraft to carry people as soon as 2024. Acting Administrator Billy Nolen said in a speech in June that the agency is on track to meet that goal, but the timing will be dictated by the safety of the new designs. 

“This is harder than people generally understand,” said John Hansman, a professor at the Massachusetts Institute of Technology who co-authored a paper on the challenges facing the new electric-powered, vertical-takeoff vehicles. “You’re pushing the state of the art in multiple dimensions at the same time.” Hansman is also an adviser to Electra.aero, which is developing a hybrid-electric plane.

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Learning experiences

One of the most high-profile crashes occurred on Feb. 16 in a remote testing facility near Jolon, California. A physical component on Joby’s six-propeller craft broke in midair, three people familiar with the incident told Bloomberg. 

The crash may not threaten the company’s long-term plans because the aircraft was operating at speeds far higher than the maximum 200 miles per hour it will fly in service, two of the people said. A flight track by the website ADSBexchange.com showed it was traveling at 273 miles per hour before it disappeared.

Joby declined to comment. The National Transportation Safety Board, which hasn’t completed its investigation, has only said the aircraft had an unspecified component failure.  

Boeing suffered two crashes in 2019: Aurora’s prototype air taxi on June 4, and the company’s experimental, pilotless cargo aircraft on June 21. Aurora’s was caused by a computer’s erroneous command to shut engines and Boeing’s was due to gusty winds, the NTSB said.

“We gained valuable knowledge and experience that will benefit programs across the company,” Boeing said in an emailed statement. The company is continuing its development work in a partnership with Kitty Hawk known as Wisk Aero LLC. 

Managing mishaps

The accidents shouldn’t be viewed as comparable to the rare mishaps during flight testing of traditional aircraft, said Walter Desrosier, vice president for engineering and maintenance at the General Aviation Manufacturers Association trade group. Significantly greater protections are taken in advance of test flights where pilots and engineers are going to be aboard, Desrosier said. 

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“When we have the ability to test things without humans, you can do additional things because you can manage the risks,” he said. All but one of the nine accidents reviewed involved craft being flown remotely. 

Kitty Hawk’s Heaviside 2 crashed in a field near Tres Pinos, California, on Oct. 17, 2019, after a software error led to control problems, according to an NTSB report. A remote pilot attempted to land the hybrid aircraft designed to carry one person, but it wasn’t capable of touching down in a field while moving forward and suffered substantial damage, the NTSB said. 

The company told investigators it was revising the software and also changing its procedures. Kitty Hawk didn’t respond to requests for comment. 

Similar failures of software or aircraft structures have occurred during development of human-carrying craft, but go unnoticed because they occur in a lab, not during a flight, Desrosier said. Unlike crashes, such failures mostly aren’t publicly reported.

Fire hazards

The crashes and incidents involving these new-age aircraft have occurred for a variety of reasons, from failures in carbon-fiber structures to breakdowns in computer-human interactions. They highlight some of the design challenges with the technology. 

Century-old flight controls used by traditional aircraft are being replaced in some cases by computerized motors. While some initial models will be guided by traditional pilots, the goal is to transition to robotic flight. 

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Instead of liquid fuels, they will be powered by lithium-based batteries, creating new questions about fire hazards and ensuring an adequate charge.

A Jan. 22, 2020, fire destroyed a prototype of Eviation Aircraft’s electric-powered, nine-passenger commuter plane in Prescott, Arizona. The fire started in a ground-based battery that isn’t part of the plane’s main power pack, the company said in an email.

“We learned a valuable lesson from the event,” the company said in an emailed statement, adding that it has taken multiple steps to protect the lithium-based batteries from overheating and fire.

Similarly, Lilium, which is designing an aircraft that uses electric-powered jet engines to take off vertically, said in an emailed statement that it had upgraded safety measures in its battery system after a fire on Feb. 27, 2020, at an airport near Munich. 

Future bets

The accidents haven’t stopped established companies from clamoring to invest in air-taxi startups or to order still-uncertified aircraft. Package shipping kingpins FedEx and United Parcel Service both have linked up with eVTOL startups and major airlines — including American Airlines Group and United Airlines Holdings — also have placed bets on the industry.

But a May report by the Government Accountability Office on the prospects of electric-powered air taxis said one of the biggest challenges facing the industry and regulators is ensuring buy-in from the public. 

“Acceptance of large numbers operating in close proximity to people and buildings will require a concerted effort on the part of industry and government to show these aircraft’s safety by demonstrating safe, reliable operations,” the GAO report said.