The Joby S4, the Part One Thirty-Five Air Carrier Certificate the FAA Already Issued, and the Gap Between First Permission and First Passenger

Joby Aviation’s S4 has secured an FAA operating certificate, attracted more than $2 billion in institutional investment, and completed over 1,000 test flights. What it has not yet secured is FAA type certification - the airworthiness approval required before a single fare-paying passenger can board. That gap between first permission and first passenger is the defining story of the eVTOL industry right now.

What the Joby S4 Actually Is

The S4 is a five-seat electric aircraft - one pilot, four passengers - powered by six tilting prop-rotors. At takeoff, all six rotors point vertically, lifting the aircraft like a scaled-up multirotor drone. In cruise, four rotors tilt forward to pull the aircraft like conventional propellers. The remaining two fold flat against the airframe to reduce drag.

The result is an aircraft with the takeoff footprint of a helicopter and the cruise efficiency of a fixed-wing airplane. Top speed is approximately 200 mph. Range per charge is roughly 150 miles. There is no combustion engine anywhere on the airframe.

Why Six Rotors Instead of One

A conventional helicopter concentrates reliability into a single high-quality system. When something fails, recovery depends on a trained pilot executing autorotation correctly under pressure.

Joby’s design inverts that logic. Six independent propulsion paths, managed by flight control computers cycling at extremely high rates, mean the aircraft can lose multiple motors and maintain controlled flight. The safety case relies on what the system does in the next ten milliseconds, not what a pilot does in the next ten seconds.

The tradeoff is mechanical complexity - six motors, six controllers, six rotor assemblies, and the software integrating all of them. For an aircraft carrying commuters rather than rated pilots, the safety argument is compelling.

The Company Behind the Aircraft

JoeBen Bevirt founded Joby Aviation in 2009 - before DJI existed in any meaningful form, before practical eVTOL was more than a dissertation topic. When the broader eVTOL investment wave arrived in the late 2010s, Joby had already been in hardware development for years.

In December 2020, Joby acquired Uber Elevate, Uber’s aerial rideshare division, adding engineering talent, urban mobility research, and software infrastructure. The company went public through a SPAC merger in 2021, putting their financials - cash position, burn rate, certification milestones - into public quarterly filings.

What the Institutional Commitments Signal

Toyota invested $394 million across multiple rounds. Toyota’s investment philosophy is methodical and manufacturing-oriented; their involvement gives Joby access to production expertise almost no aerospace startup has ever had.

Delta Air Lines committed $100 million and signed on as Joby’s commercial launch partner. The plan at JFK in New York is a vertiport within the terminal footprint, so a passenger arriving on a transcontinental flight can connect to a Joby departure directly. The projected travel time to Midtown Manhattan is roughly 12 minutes, compared to 45 to 90 minutes by ground depending on conditions.

The U.S. Air Force has been evaluating Joby through its Agility Prime program, and Joby has flown their aircraft at Edwards Air Force Base - the same facility where Chuck Yeager broke the sound barrier and where the Space Shuttle landed after reentry. That operational context is a credibility marker no press release can replicate.

What the Part 135 Certificate Actually Means

In August 2023, the FAA issued Joby Aviation a Part 135 Air Carrier Certificate. Coverage at the time described this as FAA approval or a major regulatory clearance. That framing was incomplete.

A Part 135 certificate is an operating certificate. It authorizes the company to run an air taxi business and governs pilot management, maintenance programs, and operational control procedures. It is, in effect, the business license.

It is not, under any interpretation, an airworthiness certification for the aircraft. That is a separate regulatory track, governed by a separate part of the code, evaluated by a separate process. Getting the operating certificate first is genuine progress. It is not the same as the second part.

The Type Certificate: Why It’s the Hard Part

Type certification for a powered-lift aircraft - the regulatory category eVTOL falls under - is one of the most complex problems the FAA has been asked to solve. The powered-lift category existed in the Federal Aviation Regulations primarily because of tiltrotor programs like the V-22 Osprey, but the civil airworthiness standards for certifying a powered-lift aircraft to carry fare-paying passengers were never fully developed.

When Joby and other eVTOL developers arrived with real aircraft, the FAA had to construct a certification framework in parallel with the aircraft being built. The compliance requirements cover battery management systems, motor controllers, structural loads, flight control software, avionics architecture, emergency procedures, acoustic signature, and dozens of other technical areas. More than 1,000 individual requirements in total, each requiring testing, documentation, and sign-off.

The FAA structured Joby’s certification into five stages. Stage Four - now complete - is where the FAA validated the compliance methodology itself. Completing Stage Four means the approach has been accepted: if Joby demonstrates what they have committed to demonstrating, they will have shown compliance with the standards. Stage Five is where they physically prove it, requirement by requirement.

The Honest Timeline

Joby originally targeted commercial service by 2024. That did not happen. The current stated goal is 2025. Many analysts tracking eVTOL certification closely consider 2026 a more realistic expectation for actual revenue passenger service in initial constrained markets - not because the program is failing, but because thorough certification takes time, and thorough is exactly what this category requires.

The flight test record provides context. Joby has logged more than 1,000 test flights, exercising the aircraft across its full performance envelope including intentional system failures during controlled testing. That is not a prototype demonstration program. That is a certification data-collection effort.

The Acoustic Advantage Nobody Talks About Enough

Joby has published acoustic measurements showing the S4 on approach is dramatically quieter than a comparable conventional helicopter. At typical urban overflight altitudes in cruise, the aircraft approaches the threshold of detectability against normal city ambient noise.

This matters for reasons beyond comfort. The political and community acceptance problem for urban air mobility is real. Zoning hearings for proposed vertiport sites will draw neighbors with questions about noise. An aircraft that is genuinely quieter than what people imagine when they hear “helicopter operations” changes that conversation in a material way.

The Battery Constraint

Current lithium-ion energy density supports the 150-mile range Joby is targeting. That is workable for urban air mobility - crossing a metropolitan area, connecting to an airport, bypassing a congested corridor. It does not make this an intercity aircraft at current battery technology, and the physics are fixed.

Thermal management of a large battery pack during aggressive climb profiles and repeated fast-charge turnaround cycles is an active engineering challenge. Getting the FAA comfortable with a battery system’s behavior across its full service life - including degradation over hundreds of charge cycles and failure modes under edge conditions - is among the detailed certification elements still in progress.

Why This Matters Beyond Joby

The certification framework the FAA is building to certify the S4 will govern this class of aircraft for the next generation. The standards written for Joby’s battery system become the standards every subsequent eVTOL developer works to. The operational procedures being developed for vertiport approaches, for ATC sequencing of powered-lift aircraft in dense urban airspace, for pilot type ratings in this category - all of it is being built for the first time right now.

New aircraft categories mean new airspace structure, new procedures, and eventually new phraseology. Controllers currently have no standardized method for sequencing a powered-lift aircraft on a vertiport approach alongside conventional traffic on a parallel instrument approach. ATIS broadcasts at airports near vertiports will eventually carry information that fits no current template. The people building all of that infrastructure are pilots and controllers.

Target pricing, per Joby’s public statements, is in the range of a premium car service - not private aviation costs, but not flat-rate rideshare either. The intended market is business travelers and time-sensitive commuters.

Key Takeaways

The Joby S4 is a five-seat, six-rotor electric aircraft with a 200 mph top speed and 150-mile range, using redundancy-by-architecture rather than single-system reliability.
The August 2023 Part 135 Air Carrier Certificate authorizes Joby to operate an air taxi business - it is not aircraft airworthiness approval; type certification is the separate, harder milestone still in progress.
FAA type certification for powered-lift aircraft required building an entirely new regulatory framework; Joby has completed Stage Four of five, with Stage Five requiring physical proof of every compliance requirement.
Commercial service was originally targeted for 2024, then 2025; analysts broadly expect 2026 as the more realistic date for initial revenue passenger operations.
The certification standards and operational procedures the FAA is developing for the S4 will define how this entire aircraft category is regulated for the next generation.