The eVTOL Certification Bottleneck: Engineering Teams Are Ready, Regulators Are the Constraint

The aircraft are, by any reasonable engineering measure, ready to be evaluated. Joby Aviation has logged thousands of flight hours on its S4. Archer’s Midnight has completed piloted transition flights. Wisk’s Cora has been flying in New Zealand since 2017. The vehicles exist. The engineering teams have done the work. The constraint now is not titanium or software or battery chemistry—it is the pace at which the FAA and EASA can finalize the special conditions that define what “compliant” actually means for a powered-lift aircraft.

This creates a genuinely unusual situation in aerospace engineering: manufacturers are not blocked on technical readiness. They are blocked on regulatory readiness. And in the interim, they are being asked to design to a target that keeps moving.

Understanding what that actually means for engineering teams—the concrete workflow implications, the requirements management challenges, the program risk exposure—requires looking past the press releases and into how certification actually works for a novel aircraft category.

Where the Regulatory Frameworks Actually Stand

The FAA’s primary vehicle for certifying eVTOL aircraft is the powered-lift special class designation under 14 CFR Part 21.17(b), supplemented by aircraft-specific G-1 Issue Papers that establish the certification basis for each applicant. EASA is using a parallel structure under its Special Condition for Small Category VTOL (SC-VTOL), first issued in 2019 with subsequent amendments.

Neither framework is final in the sense that matters most to engineering teams: the means of compliance—the specific methods, tests, and analyses that constitute proof of conformance—remain under active negotiation between applicants and regulators on most substantive topics. FAA Issue Papers covering areas like propulsion system reliability, fly-by-wire airworthiness, battery thermal runaway containment, and human-machine interface certification are open, under revision, or conditionally closed for every active applicant.

EASA’s SC-VTOL has fared somewhat better in terms of document completeness, but its Acceptable Means of Compliance (AMC) documents, which translate the special conditions into engineering substance, have seen multiple revision cycles since 2021. AMC-VTOL Issue 2 introduced meaningful changes to enhanced category requirements that required applicants to revisit structural substantiation and failure mode analyses already in progress.

The working assumption inside most eVTOL programs is that the core certification basis for leading applicants will be substantively stable by late 2026 or early 2027. That assumption has slipped roughly eighteen months from where it stood in 2024.

What “Designing to Evolving Standards” Actually Costs

When a standard shifts after engineering work is complete, the cost is not just rework. The deeper cost is traceability debt—the gap between what requirements the engineering team was working to and what requirements the certification record needs to show.

Consider a concrete example. A structural engineering team designs a primary airframe joint to a specific ultimate load factor derived from their current understanding of SC-VTOL structural requirements. Eighteen months later, EASA amends the AMC to require a different load case envelope for certain emergency descent conditions. The joint may still be compliant—or it may need to be redesigned. But before anyone can determine that, someone has to trace from the amended requirement down through the system requirements, the design specifications, the analysis reports, and the test evidence to find out what was derived from the old assumption and what wasn’t.

In a document-based requirements system—a DOORS database where requirements live in modules linked by manually maintained trace matrices—this is a multi-week exercise that produces answers engineers do not fully trust. In a graph-based system where requirements, design artifacts, analyses, and test results are nodes in a connected model, the impact set of a changed requirement is visible in minutes.

This distinction is not theoretical. Engineering directors at multiple eVTOL programs have described the same pattern privately: when a regulator-driven requirement change arrives, the immediate question is not “can we still comply?” It is “how long will it take us to find out what we need to look at?” The answer to that second question is what determines program velocity in a shifting-standards environment.

Means of Compliance Documents: Progress Without Finality

The practical mechanism that allows certification programs to advance without a fully finalized ruleset is the Means of Compliance (MoC) document—a bilateral agreement between the applicant and the certifying authority on how a specific requirement will be demonstrated.

MoC documents are not the same as the requirement being satisfied. They are agreements on method: this is how we will show compliance, and the regulator has agreed that showing it this way is acceptable. Once a MoC is agreed, the engineering team can design tests, write analyses, and build substantiation evidence with confidence that the method won’t be challenged later—even if the underlying regulation is still being refined.

The strategic implication is significant: engineering teams that have invested in deep engagement with their certification authority—building a library of agreed MoC documents across the major technical areas—are insulated from a meaningful portion of the regulatory uncertainty. They may still face requirement changes that require rework, but they face fewer situations where completed work is methodologically challenged.

Joby has been explicit about this in its investor communications, describing its relationship with the FAA as a key competitive asset. The company entered its G-1 Issue Paper process earlier than most competitors and has accumulated one of the broadest sets of agreed MoC positions in the industry. Archer has pursued a similar strategy, explicitly modeling its certification program on Joby’s playbook. Both companies have also engaged EASA in parallel validation discussions, recognizing that European certification is not a distant follow-on but a near-simultaneous commercial requirement.

Less visible, but worth noting: the companies whose MoC negotiation strategies have been most effective tend to be the ones that can present their engineering substantiation in the most structured, traceable form. Regulators, particularly FAA certification engineers working through Issue Papers, respond better to applicants who can show exactly where a specific analysis lives in the certification basis and what it connects to. That is a requirements management capability, not just a technical one.

Issue Papers: The Negotiation Infrastructure

An Issue Paper is, at its core, a documented disagreement—or a documented agreement in progress—between an applicant and the FAA on how a certification requirement applies to their specific design. The IP process is how novel aircraft features get adjudicated: the applicant proposes a position, the FAA responds, and the document evolves through multiple revisions toward a “closed” status that reflects mutual agreement.

For eVTOL programs, the Issue Paper landscape is extensive. A typical powered-lift applicant has dozens of open or conditionally closed IPs covering topics from distributed electric propulsion failure modes to pilot training requirements to lithium-ion battery crashworthiness. Each open IP represents a requirement that is not yet fully defined for that program.

The engineering management challenge is that IP closure is not entirely within the applicant’s control. Closure requires FAA resources—specifically, certification engineers with the technical depth to evaluate novel positions on novel systems. The FAA has acknowledged publicly that it is resource-constrained in this area. The agency has made additional hires and has used Organization Designation Authorization (ODA) structures to expand its effective capacity, but the fundamental bottleneck remains: there are more eVTOL programs seeking IP closure than there are FAA engineering-hours available to close them.

The programs managing this constraint most effectively are doing two things. First, they are prioritizing IP closure on the items most likely to drive design changes—getting regulatory position confirmed on the requirements most deeply embedded in the engineering architecture before freezing the design around them. Second, they are maintaining their engineering documentation in a state that allows rapid substantiation updates when an IP closes in an unexpected direction. That second capability is, again, a requirements and document management capability more than a purely technical one.

Stage-Gate Reviews in a Moving-Target Environment

Traditional aerospace development uses stage-gate reviews tied to development phases: Preliminary Design Review, Critical Design Review, and so on. The implicit assumption is that the certification basis is largely stable by PDR and substantially fixed by CDR.

For eVTOL programs, that assumption has been false for most of the last five years. The result has been a practical renegotiation of what stage-gate reviews mean in a novel-category certification environment.

The most defensible approach, which several programs have adopted explicitly, is to tie stage-gate criteria not to calendar milestones but to Issue Paper and MoC closure status. A CDR-equivalent review does not happen when the calendar says it should—it happens when a defined set of foundational IPs are closed and the certification basis is stable enough to support design freeze. This sounds obvious, but executing it requires program management discipline to resist the calendar-driven pressure that comes from investors, partner timelines, and commercial agreements.

The programs that have resisted this pressure—accepting schedule delays in exchange for genuine certification basis stability before design freeze—are the ones that are not currently re-opening design work to address IP resolutions that arrived after CDR. The programs that held to their calendar-driven gates are now doing exactly that re-work, which is more expensive and slower than it would have been if the gate had been held.

Who Is Best Positioned When Standards Finalize

Predicting certification timing is hazardous. But assessing which programs will be best positioned when standards do finalize is more tractable, because the relevant factors are visible now.

Joby Aviation has the deepest MoC library, the most mature relationship with the FAA, and has been flying a conforming aircraft longer than any other US applicant. Its manufacturing certification work under Part 21.139 is also advanced. The primary risk is not technical or regulatory—it is that the timeline has extended far enough that the commercial window Joby anticipated is becoming more contested.

Archer Aviation has executed the certification playbook well and has benefited from its relationship with United Airlines, which has provided both funding and operational requirements discipline. Its Midnight configuration is simpler in some respects than Joby’s, which reduces certification surface area.

Wisk Aero is pursuing autonomous operations from the start, which makes its certification path structurally more complex—the DAL requirements for a vehicle with no pilot backup are substantially more demanding. But Wisk’s operational experience in New Zealand and its backing from Boeing give it durability through an extended timeline.

Lilium presents the most complex picture. The original company’s insolvency in 2024 and subsequent acquisition of its assets creates certification continuity questions. The acquiring entity, which has restarted development under a restructured program, faces the challenge of demonstrating to both EASA and FAA that the certification basis from the prior program can be maintained and extended—not trivially established.

The common thread among the best-positioned programs is not the sophistication of their aircraft. It is the quality of their certification evidence infrastructure: how well their requirements are traced, how quickly they can respond to regulatory changes, and how much of their substantiation exists in forms that regulators can evaluate efficiently. Companies that invested early in structured, machine-readable requirements management—rather than document repositories—are accumulating a compounding advantage as the certification basis converges.

Tools like Flow Engineering, which model requirements as connected graphs rather than document hierarchies, allow teams to surface impact sets for regulatory changes in minutes and maintain bi-directional traceability from regulatory requirement through system requirement, design artifact, and test evidence. At the scale of a full-vehicle certification program, that capability is not a productivity convenience—it is a risk management asset when the regulatory target is moving.

The Honest Assessment

The eVTOL certification timeline will continue to slip, and the programs that assume otherwise are taking on unpriced risk. The FAA and EASA are not being obstructionist—they are doing serious engineering work on genuinely novel problems, and the safety stakes are real. But the pace of regulatory completion is a constraint that no amount of engineering excellence on the applicant side fully offsets.

The practical implication for engineering teams is to optimize for adaptability rather than schedule. Design to the most current understanding of the certification basis while maintaining the architectural flexibility to absorb changes. Invest in MoC agreement breadth, not just depth on your current design assumptions. Run stage-gate reviews against IP closure status, not calendar dates. And maintain your requirements and certification evidence in a form that makes impact assessment fast when the next regulatory change arrives—because it will.

The aircraft are ready. The engineering teams are ready. The companies that will win the certification race are the ones that are also ready for the requirements to change one more time before the finish line.