There are almost as many start-up eVTOL aircraft developers as there are industry observers who have argued that if this new air transportation mode suffers a single fatal accident it could be its last. Aviation regulators have made it clear they will hold the envisaged eVTOL air taxi services to the same safety standards as current commercial operations, but some say there is a case for above-and-beyond protection like that promised by systems such as whole-aircraft parachutes that deploy automatically to ensure a soft landing for a failed air vehicle.
The equipment is already standard on Cirrus Aircraft’s SR20, SR22, and SF50 Vision Jet general aviation aircraft, using a device developed by the manufacturer and Ballistic Recovery Systems, which is also creating a version for Transcend Aerospace’s Vy 400 VTOL aircraft. Cirrus has released a video describing how one of its owner-pilots safely deployed the parachute after an engine failure.
Bye Aerospace’s eFlyer all-electric fixed-wing models are set to use a parachute recovery system being developed by Aviation Safety Resources (ASR). The company's president and CEO Larry Williams believes parachutes should be firmly on the AAM safety agenda.
“For any designer of an aircraft, and especially a new company with no history [in aviation], if there is a safety technology that can make a difference it should be on the aircraft,” Williams told FutureFlight. The company says it is developing a version of its Xtreme Rapid Deployment technology for a ballistic parachute specifically intended for eVTOL aircraft that it says would not require forward-speed to deploy.
However, companies developing eVTOL aircraft mainly for passenger-carrying air taxi services for the most part are not embracing the case for whole-aircraft parachutes. Most of the front-runners in the race to bring vehicles into commercial service between now and 2026 have no plans to use the technology, with all insisting that their aircraft will be certified with high levels of system redundancy to guard against propulsion system failures and with the means to land safely in an emergency.
The exception is Wisk Aero, which is developing the two-seat Cora eVTOL vehicle, and also a larger, longer-range aircraft that would be operated fully autonomously. The company says it intends to include a safety parachute but has yet to specify which type or how it would be deployed without a pilot on board, and with flights monitored, rather than being remotely piloted, by controllers on the ground.
Germany-based Volocopter, which is working toward EASA type certification for its two-seat VoloCity aircraft, pointed out that the European regulator’s Special Conditions-VTOL (SC-VTOL) rules require safety performance equating to a 10-to-the-minus-nine probability of catastrophic failure. This equates to a rate of one in every one billion flight hours, which is the same standard as for commercial airliners.
“In fact, a parachute may not be the optimal safety mechanism for intracity flights (for example, unpredictable gusts of city air), because once deployed, it cannot be controlled,” the company said in a written statement. “There are other safety options for this SC-VTOL—for example, predefined alternate sites for an emergency landing along the aircraft’s flight path. While, subjectively, the mere presence of a parachute makes some people feel more comfortable, factually they make the system less safe.”
Jaunt Air Mobility intends to certify its Journey eVTOL aircraft to the FAA’s Part 29 rules, which apply to today’s commercially operated rotorcraft. The company questions the effectiveness of whole-aircraft parachutes for the low-altitude, urban operations envisaged for eVTOL vehicles generally.
“We will not require a ballistic parachute,” Jaunt’s chief operations officer, Jesse Crispino, told FutureFlight. “Due to our patented slowed-rotor technology, we can either autorotate [in case of a system failure] or glide to make a safe, controlled landing. This makes us safer than any helicopter or aircraft today.”
Jaunt says that in the event of complete propulsion system failure, the Journey’s pilot would be able to autorotate from any altitude or glide using the wing on which its cruise-flight propellers are installed. From an altitude of 1,200 feet, the company says, the flight crew would have options to safely land within a radius of eight square miles. It says it has dual-redundant propulsion and flight control systems, with two motors on the main rotor system and only two of the four propellers required to operate safely.
However, according to Crispino, some eVTOL developers are considering parachutes because their designs cannot glide or autorotate. He claimed that while EASA has addressed the role of ballistic parachutes in the SC-VTOL rules, it may penalize the aircraft in terms of certified operating limits for having what he described as non-steerable parachutes.
“Ballistic parachutes need enough altitude to deploy, and they might be flying at somewhere between just 400 and 1,000 feet,” said Crispino, who is a former U.S. Navy test pilot. “It takes about three seconds to realize that something is really wrong and the pilot needs some altitude so that the parachute doesn’t become FOD [foreign object damage]. If there is a catastrophic failure, the parachute could go through the propellers, and also they are not steerable so the pilot gets no vote as to where the aircraft lands.”
Joby also insisted that the high levels of redundancy built into its four-passenger eVTOL design obviate the need for a parachute. The company, which recently lost one of its two prototype aircraft during a flight test accident, said that the vehicle can safely operate after failures to the motors, batteries, or electric propulsion units and also has the option to land vertically or glide to the ground on its wing.
Similarly, Lilium maintained that it is building in sufficient redundancy for its Lilium Jet, which features a propulsion system based on 30 ducted fans. The seven-seat aircraft also has a wing.
EHang—which is working to certify its EH216 Autonomous Aerial Vehicle with the Civil Aviation Administration of China—told FutureFlight that it sees no need for a whole-aircraft parachute. Crucially, the aircraft in the EHang fleet, which will also include a larger and longer-range VT-30 model, are intended to be completely autonomous with no pilot on board.
The company said that by having full redundancy for all major flight components and what it described as a built-in fail-safe system that assesses the vehicle's health in real-time, it will avoid unpowered landings. It also shares Jaunt’s misgivings about inherent safety risks in deploying ballistic parachutes.
“If any malfunction or abnormal condition occurs, multiple backups will seamlessly come online to take over, and the fail-safe system would take contingency plans to ensure the safety of passengers, including an urgent powered landing,” said a company spokesperson in a written statement. “Our command-and-control center will also step in and provide double assurance of safety to our vehicles and passengers.”
At ASR, Williams remains concerned that eVTOL pioneers are being shortsighted and, in the race to market, are reluctant to incorporate other new systems. He warned that they are in danger of disregarding public safety concerns and that just one accident could undermine the entire advanced air mobility business model.
Williams pointed to a 2017 study by the University of Michigan into public opinion about the prospect of what researchers categorized as flying cars. This found that just under 80 percent of the 508 American adults surveyed said it would be extremely or very important for new aircraft to be fitted with a parachute. However, the study (download here) doesn't appear to have clearly differentiated between eVTOL designs intended for personal transportation that could be certified under light sports airplane rules and vehicles to be certified under more complex rules for commercial operation.
ASR says it has already done more than 50 drop tests with its parachute system and has more such tests planned as it refines the canopies it is using. In addition to Bye Aerospace, Williams said, the U.S. company has been collaborating with two unidentified VTOL aircraft developers, including one working on a hydrogen-powered design. He said that the FAA has been “very cooperative” but indicated that previous efforts to work with European manufacturers had been compromised by the technical penalties imposed by EASA to incorporate parachutes into the safety system.
In a discussion paper titled One in a Billion (download here), Williams takes issue with the common claim by eVTOL manufacturers that their electric propulsion systems have more than sufficient levels of redundancy. “Depending on the design and the number of rotors, etc., you cannot effectively lose one motor or rotor,” he argued. “Why? Asymmetric thrust. In other words, the loss of one rotor of let’s say five causes you to reduce the power [lift] on the corresponding opposite rotor; otherwise you produce thrust that will tip the vehicle over and/or cause loss of yaw in forward flight. So, as an example, if you lose lift on the front right rotor, you will need to reduce power on the left rear rotor.”
ASR maintains that its parachute would deploy and inflate on an eVTOL aircraft in no more than two seconds. It expects to be able to sell the devices for no more than 2 percent of the total cost of each vehicle, which Williams said would be comparable to the cost of “a good aviation radio.”
