Joby Aviation, the S Four, and the FAA Certification Gauntlet That Will Set the Template for Every eVTOL That Follows

Joby Aviation’s S4 is an electric vertical takeoff and landing aircraft that lifts off like a helicopter, transitions to fixed-wing cruise, carries one pilot and four passengers, and produces approximately 45 decibels of noise on approach - quieter than a normal conversation. The company has been flying test aircraft since 2017, is currently in Stage 4 of the FAA’s five-stage certification process, and is targeting a type certificate in 2026 or 2027. What makes this story significant beyond one aircraft is that the regulatory framework the FAA is building around the S4 will become the certification template for every comparable eVTOL that follows.

What the Joby S4 Actually Is

The S4 uses six electric motors driving six tilting rotors. For takeoff and hover, those rotors point upward. As the aircraft accelerates, they tilt forward and the wing takes over lift duties - the same trade that fixed-wing aircraft use to achieve efficient cruise. Without that transition, the battery range would be far shorter.

Published performance numbers: top speed of approximately 200 mph, range of approximately 150 miles per charge. The footprint is roughly that of a light twin.

The term “eVTOL” covers an enormous range of hardware, from consumer drone derivatives to serious aerospace programs. The S4 is in the serious category.

Why the Noise Numbers Matter More Than the Speed Numbers

Joby’s acoustic testing data shows the S4 at approximately 45 decibels on approach. For reference, a conventional helicopter on approach registers between 80 and 100 decibels. A normal conversation is around 60 decibels. The S4 on approach is quieter than both.

The physics behind this is well understood. Distributing thrust across six smaller rotors instead of one large rotor means each blade moves through the air at a lower tip speed. Tip speed is the dominant driver of rotor noise. Lower tip speed produces dramatically lower acoustic signature.

This was never purely an engineering constraint. The entire urban air mobility business model depends on it. No city planning board approves a rooftop vertiport producing helicopter-level noise every few minutes. The 45-decibel target was a commercial requirement from the beginning, and the S4’s design reflects that priority.

Why eVTOL Range Is Limited - And Why That’s the Point

The S4 runs on lithium-ion battery technology, which currently delivers around 250 watt-hours per kilogram. Jet-A carries approximately 12,000 watt-hours per kilogram. That gap is not a rounding error. It is the reason the S4 covers 150 miles rather than 450.

That constraint is actually the entire point of the market these aircraft are targeting. Short-hop urban routes - airport connectors, city-to-hub runs - are where ground traffic costs passengers 45 to 60 minutes that a 10- to 12-minute flight eliminates. The Los Angeles basin, the Bay Area, and the New York metro are markets where that time compression supports a ticket price that makes the economics work.

Solid-state battery chemistries in development could roughly double energy density within the decade, which would expand the operational envelope significantly. That trajectory is a reasonable long-term bet. It is also a bet on future technology, not current hardware.

How the FAA Certifies an Aircraft That Has Never Existed Before

The FAA certifies aircraft within established categories: Normal, Transport, Rotorcraft. The S4 fits none of them. It lifts off vertically, transitions to fixed-wing flight, and presents a failure-mode landscape that does not map onto any existing aircraft type.

For genuinely new aircraft, the FAA uses a pathway under 14 CFR Part 21 called special class. The agency works with the manufacturer to define specific airworthiness criteria for that aircraft. Once that criteria document is established, it governs the entire certification program.

For Joby, the FAA issued that document in 2022. It is called the G-1 criteria document. It defines what Joby must demonstrate: noise characteristics, structural loads, flight envelope, failure modes analysis, electrical system redundancy, and the complete systems picture. The G-1 is publicly available from the FAA and is the closest thing to a rulebook for this class of aircraft that currently exists.

Why the Transition Phase Is the Hardest Part to Certify

During the shift from vertical to horizontal flight, the S4 is aerodynamically neither a helicopter nor a fixed-wing airplane. Six spinning rotors interact with a lifting wing, a fuselage, and real-time fly-by-wire control inputs simultaneously. The aerodynamic complexity during this transition phase is the most technically demanding aspect of the entire certification.

The FAA requires that if any single system fails during transition, the aircraft must be able to recover and land safely. Demonstrating that across six independent electric drive systems, a battery management system, a flight control computer, and a tilting rotor mechanism does not happen quickly.

This is why the S4’s certification is projected to take five to seven years of active test work - requiring thousands of flight hours and millions of simulation hours on top of that.

Where Joby Stands in the Certification Process Right Now

As of mid-2026, Joby is deep into Stage 4 of the FAA’s five-stage certification process. Stage 4 is where the serious structural and systems testing occurs - the testing that generates the airworthiness evidence the FAA actually reviews before signing a type certificate.

Joby has been flying test aircraft since 2017. Their production-representative test vehicle has been flying since 2023. The company has accumulated over 1,000 test flights across its fleet.

The originally stated certification target covered the 2025–2026 window. That window has not produced a signed type certificate. Aviation certification timelines slip - that is nearly a law of physics for programs representing genuinely new aircraft categories. The most realistic current projection is a type certificate in 2026 or 2027, with initial commercial service on limited routes shortly after, and meaningful operational scale in the 2028–2030 timeframe.

How Military Testing Feeds FAA Certification

The U.S. Air Force runs a program called Agility Prime, designed to advance eVTOL development by using Department of Defense flight hours to generate airworthiness data that feeds directly into FAA certification evidence packages. Joby has been flying at Edwards Air Force Base under Agility Prime since 2021.

Those military test hours are not separate from the FAA certification program. They are formally part of it. The Air Force wants the operational capability, the FAA needs the airworthiness data, and the manufacturer receives funded flight hours. The arrangement is structured to accelerate certification, and it does.

The Competitive Landscape

Archer Aviation has an aircraft called Midnight, also using a tilting six-rotor configuration, with a commercial partnership with United Airlines. Archer is behind Joby in the certification process but is making consistent progress.

Lilium, a German company, pursued an innovative design using electric ducted fans embedded in the leading edge of the wing rather than open rotors. Lilium filed for insolvency in 2024. The assets were subsequently acquired and a reconstituted effort is attempting to continue the program. Lilium is the cautionary tale: technically ambitious, chronically undercapitalized. Aviation certification timelines do not compress for companies that run out of capital.

Wisk Aero is pursuing a fully autonomous design with no onboard pilot - a different and more complex certification path from a regulatory standpoint.

The competitive picture confirms something important: even companies with serious engineering teams, serious funding, and serious regulatory relationships require the better part of a decade to reach service entry. Capital to outlast timeline slippage is as important as technical capability.

Joby’s Commercial Strategy

Delta Air Lines is Joby’s domestic commercial partner - not just an investor but the intended operational partner for airport integration across the United States. The concept positions a Joby flight as a Delta connection: a passenger lands at a major hub, books a Joby ride through the Delta app, and reaches a downtown vertiport in minutes rather than an hour in traffic. Joby operates the aircraft; Delta provides the brand trust, the reservation infrastructure, and the airport relationships.

That structure addresses the hardest problem in urban air mobility, which is not the aircraft - it is the customer relationship. Where does a first-time passenger learn to trust something they have never heard of? Delta answers that before it becomes a question.

Toyota is a manufacturing partner with investments totaling several hundred million dollars across multiple rounds. The manufacturing challenge for eVTOL is frequently underestimated. Producing two aircraft per year for a test program is categorically different from producing 200 per year for commercial operations. Toyota’s industrial depth in complex, high-volume manufacturing is embedded in the company at an early stage - when that depth is cheapest to acquire.

Joby went public in 2021 through a SPAC merger and has raised substantial additional capital since. Financial runway exists. Whether it is sufficient depends on how long the remaining certification work takes.

Why Joby’s Certification Matters Beyond Joby

Whatever the S4’s commercial outcome, the regulatory framework being built around it is not company-specific. The G-1 criteria document, the failure mode analysis methodology for tilting-rotor eVTOL, the acoustic certification standard, the testing protocols for fly-by-wire transition management - all of it becomes the template. Every company that certifies a comparable aircraft after Joby inherits years of regulatory groundwork that has already been cut.

Joby is simultaneously building an air taxi and writing the certification playbook for a new class of aircraft. Those are different contributions with different beneficiaries, and the second one is underappreciated.

The infrastructure readiness question runs on a separate and slower timeline. Vertiports require zoning approvals, noise impact reviews, high-power electrical grid connections for rapid charging, and low-altitude airspace management the current ATC system was not designed to handle at commercial traffic density. Joby can get the aircraft certified. Cities, utilities, planners, and air traffic control all have their own readiness curves that run entirely independently. The type certificate may turn out to be the easiest piece of the puzzle.

Key Takeaways

• The Joby S4 produces approximately 45 decibels on approach - roughly 35–55 decibels quieter than a conventional helicopter - making noise reduction a foundational design requirement rather than an afterthought
• The S4 is in Stage 4 of 5 in the FAA certification process, with a type certificate most realistically expected in 2026 or 2027
• The FAA’s G-1 criteria document, issued in 2022, defines the airworthiness standards for the S4 and will serve as the regulatory template for all comparable eVTOL aircraft that follow
• Delta Air Lines (commercial operations) and Toyota (manufacturing scale) are partners chosen to address the two most underestimated problems in urban air mobility: passenger trust and production volume
• Lilium’s 2024 insolvency is the sector’s clearest cautionary data point: technical innovation without sufficient capital to outlast certification timelines does not reach commercial service