There’s no question that if eVTOL aeromobility operations are to succeed at scale, they’ll need to be much, much safer than are helicopter operations today. As Sikorsky disruptive technologies lead Jonathan Hartman has pointed out, the level of safety we design into the system will determine the upper bounds of our market size.
Building an aircraft to today’s standards of one failure per million flight hours (10-6 reliability) will statistically result in one failure per year, if a fleet of 1,000 aircraft are annually logging 1,000 flight hours each. But if 50,000 aircraft are each flying 3,000 hours per year — which is the scale that many aeromobility proponents envision — the frequency of a catastrophic failure increases to one every two-and-a-half days. That will hardly be acceptable to the general public.
Hartman has proposed that large-scale aeromobility operations will require 10-9 reliability as a design standard. I don’t disagree, but I’m convinced that viable eVTOL air taxi operations will require a lot more than that. Even in today’s helicopters (which generally fall short of the 10-9 reliability standard) most accidents are due not solely to engineering failures, but to how the aircraft are operated. The familiar shorthand for this is “pilot error” — but focusing on fallible pilots alone appears to be leading the nascent eVTOL industry down a dangerous path.
In more than a decade of reporting on helicopter accidents, I’ve come to believe that it’s not the pilot but the operator of an aircraft — the entity responsible for staffing and maintaining it — that has the greater influence on safety. And, unlike the issues associated with cognitively limited pilots, the problems related to profit-focused operators can’t be automated out of an aircraft.
Today’s part 135 air taxi operators (referring to the applicable part of the U.S. Federal Aviation Regulations) are, for the most part, business owners, constantly under pressure to fly more and spend less. These financial pressures will likely be even more acute under an eVTOL business model that hinges entirely on low operating costs and high flight volumes, yet I haven’t heard anyone discussing the role that operators will play in system safety. Why not?
Part of the reason is because the National Transportation Safety Board (NTSB) hasn’t put a lot of focus on operators in the past, particularly in its investigations of helicopter accidents. The NTSB is charged with determining a “probable cause” for each accident, and it defines this probable cause in an exceptionally narrow, almost entirely descriptive way.
For example, one common cause of fatal helicopter accidents is loss of control after a pilot flies into clouds and becomes spatially disoriented. (I’ve experienced the onset of spatial disorientation in flight myself, and it’s terrifying.) Although it’s certainly possible to safely fly a helicopter in the clouds, doing so reliably requires some combination of technology — autopilots, navigation equipment — and regular instrument flight training for the pilot. Providing those is the operator’s responsibility, yet many helicopter operators skimp on technology and training as a cost-saving measure.
Operators often contribute to spatial disorientation accidents in other ways, too, such as by pressuring pilots to accept flights in marginal weather conditions. Yet the typical NTSB report for such an accident will list the probable cause as “The pilot’s failure to maintain aircraft control after becoming spatially disoriented.” In other words: “pilot error.”
Sometimes the NTSB actually goes out of its way to shift blame away from the operator and onto the pilot. In one spatial disorientation accident I dissected for a recent safety conference, the NTSB cited as a contributing factor “the pilot’s failure to follow company procedures.” What were those procedures? According to the NTSB, they were the company’s checklist for inadvertent flight into the clouds: “Fly the aircraft, climb to altitude, do not get in a hurry, and contact approach or center.”
Now, there’s nothing necessarily wrong with that advice, but it’s not particularly helpful, either. Far more salient to the accident was the fact that the operator didn’t provide the pilot with the regular instrument training he was promised. The NTSB did mention the pilot’s lack of instrument experience in its report — but cited it as a failing of the pilot, not his employer.
It should be obvious by now that claims like “80 percent of accidents are due to pilot error” reflect structural features of the NTSB’s reporting process, not deeper truths about why aircraft crash. Yet not only are eVTOL proponents not examining these statistics critically, they’re cherry picking NTSB data to make the case that they can design away all of the safety issues that afflict helicopters now.
The Uber Elevate white paper is a disturbing example of this. Uber starts its safety discussion by asserting, “To understand the path to improving safety for urban air transportation, we need to understand the root causes of historical crashes.” OK — no argument there.
However, the white paper then jumps straight into a discussion of part 135 air taxi fatalities in Alaska, pointing out that half of these were due to pilot error described as controlled flight into terrain, mid-air collisions, and loss of control. “Since half of the part 135 crashes are related essentially to poor weather data and pilots not being where they thought they were, operating only in urban areas with real-time weather and air traffic control brings existing part 135 operations to par with the safety of driving a car.”
Wait, what? By considering only the causes of air taxi fatalities in Alaska, Uber conveniently glosses over the many fatal helicopter accidents that have occurred in urban environments, which are much more relevant to its concept of operations. Accidents like this one off a Seattle rooftop helipad, which was related to the aircraft’s hydraulic system and potentially to the checklist and training provided to the pilot. Or the crash of this tour helicopter out of Las Vegas, which was attributed to inadequate maintenance, with fatigue and a lack of clearly delineated inspection steps identified as contributing factors. Even if eVTOL aircraft are designed with 10-9 reliability, they’ll still need to be operated and maintained correctly to achieve that.
And this is giving Uber the benefit of the doubt when it comes to some of the bolder safety claims in its white paper. On May 15, a helicopter used for flights by the urban air mobility pioneer Blade crashed in the Hudson River after the pilot reportedly experienced loss of tail rotor effectiveness, an aerodynamic phenomenon that can be related to the interaction between wind and the helicopter’s rotor vortices. Uber contends that the high disc loading of most eVTOL designs will make them less susceptible to a variety of dangerous aerodynamic conditions, and that autonomy will prevent the aircraft from entering potentially hazardous states in the first place — claims that are still highly theoretical. And no matter how clever its design, a small five-passenger eVTOL aircraft will always have wind and weather limitations that must be respected by the operator. If helicopters are routinely pushed to the edges of their operating envelopes, what will prevent eVTOLs from being treated the same way?
Distributed electric propulsion designs and autonomous technologies have the potential to make tomorrow’s eVTOL aircraft inherently safer than comparably sized helicopters today. But aircraft design alone won’t solve the problem of operators pushing the limits of weather, or compromising on training and maintenance — constant temptations in an enterprise with high fixed costs and tenuous margins. Given the Federal Aviation Administration’s spotty record in overseeing part 135 helicopter operators to date, it’s not clear how they’ll manage to watch over a vastly larger number of eVTOL aircraft and, potentially, many more small operators.
Some of the solutions that have enabled the enviable safety record of part 121 airline operators could work for this emerging industry, too, although they would likely come with much more regulation and consolidation than is currently being envisioned. In any case, that’s a conversation we need to be having now, rather than pretending that vehicle design can solve all of our problems. One or two high-profile fatal accidents in city centers could effectively spell an end to aeromobility — and when that happens, it won’t matter whether it was the vehicle, the pilot, or the operator to blame.