Joby Aviation, the S4 Air Taxi, and What Five Stages of FAA Certification Really Tell You About When You'll Actually Ride One

Joby Aviation’s S4 air taxi is closer to carrying paying passengers than almost any electric aircraft in the field, but the timeline that matters isn’t the flight testing - it’s the five-stage FAA type certification process. Joby has publicly said it is deep into stage four of five, further than almost any competitor, yet “deep into flight testing” and “certified” are separated by an enormous amount of work. The aircraft already flies; certification is the actual product, and it isn’t finished until the FAA signs stage five.

What Is the Joby S4 Air Taxi?

The S4 is an electric vertical takeoff and landing aircraft - an eVTOL - that seats one pilot plus four passengers. It uses six propellers mounted on tilting nacelles: the props point straight up for takeoff and landing, then rotate forward to pull the aircraft along like a conventional airplane once it’s moving. Vertical when you need it, horizontal when you want to travel efficiently.

Joby’s published numbers are a top speed of around 200 mph and a range of roughly 100 miles on a charge. It runs entirely on batteries.

The feature pilots often underrate is noise - or the lack of it. Distributed electric propulsion means spinning many small, slow propellers instead of one big fast one, and propeller tip speed is where most noise comes from. Joby has flown demonstration profiles measuring in the mid-40s on the decibel scale from about 2,000 feet away. That’s the difference between an aircraft a city will tolerate over a neighborhood and one a city will ban within a year.

Why FAA Certification Matters More Than the Aircraft

None of the performance numbers matter until the Federal Aviation Administration says the S4 can carry a paying passenger. For a novel design, the FAA runs type certification in five stages:

Stage one - conceptual design: You tell the agency what you’re building and roughly how it works.
Stage two - preliminary design: You and the FAA agree on the actual rules the aircraft will be tested against. This sounds procedural, but it is the single most contested part of the entire effort.
Stage three - detailed design: You prove your specific parts and systems meet those agreed rules, on paper and in the lab.
Stage four - testing: You test the aircraft to show it does what your documents claim - flight tests, structural tests, systems tests - flown or measured for real, with the FAA participating.
Stage five - the type certificate: The agency issues the certificate declaring the design airworthy.

Understanding these five stages is the only reliable filter for a press release.

What “Deep Into Stage Four” Actually Means

For a conventional airplane, flight testing exists to prove the design. For Joby, flight testing is no longer the hard part. The company has flown long cross-country demonstration profiles and completed the vertical-to-forward-flight transition hundreds of times. The airplane flies.

The bottleneck is what the FAA calls “for credit” testing. There is a difference between flying to learn and flying to prove. Every test that counts toward the certificate must run against an approved plan, with approved instrumentation, witnessed and documented so it survives scrutiny years later. You don’t get credit for a great-looking flight from last spring - you get credit for the flight that matched the paperwork.

Why the Certification Rules Themselves Caused Delays

Go back to stage two. For a Cessna, the rules already exist and have for decades. For an electric aircraft with tilting propellers and no single point of thrust, many rules had to be written from scratch:

How do you certify a battery pack as a primary power source?
What is the equivalent of an engine-out for an aircraft with six motors, and how many can it lose?
What does a “controlled emergency landing” even mean for a vehicle that descends onto a rooftop pad?

The FAA and these companies spent years, not months, negotiating the airworthiness criteria before a single for-credit flight could count. Joby even saw its certification basis shift partway through, when the FAA changed how it would regulate the entire category - a genuine schedule earthquake.

So when a company says entry into service is a year or two away, run it through three questions: Which stage are they in? Is their certification basis final or still moving? How much of their flight testing is for credit versus for learning? Those answers tell you more than any render.

Why Serious Money Is Behind Joby

The optimism isn’t baseless - Joby has done the unglamorous work. Toyota didn’t just write checks totaling well over a billion dollars; Toyota engineers embedded with Joby to help design the manufacturing line. Toyota understands what aviation startups keep learning the hard way: building one hand-made prototype that flies beautifully is a completely different problem from building hundreds of identical, airworthy aircraft.

Joby operates a pilot production facility in Marina, California, and is expanding manufacturing in Dayton, Ohio - the town where the Wright brothers built bicycles and then built airplanes.

Delta Air Lines has also invested, with the goal of connecting airports to city centers. Meanwhile, Joby is pursuing its first commercial launch overseas in Dubai, where it holds an exclusive arrangement and the regulator has moved quickly to build vertiports. Launching where the runway to service is shorter lets Joby build an operational record, then bring the data home.

Why this matters for pilots: a certificate from another country’s regulator is not an FAA type certificate. A Dubai launch proves the aircraft can operate and generates real-world hours and maintenance data - genuinely valuable - but the American market still waits on the American process. The U.S. finish line moves only when stage five is signed.

The Real Obstacles: Batteries, Pilots, and Infrastructure

Batteries. Energy density limits range and payload, and the constant charge-discharge cycles of an air taxi flying dozens of short hops a day are brutal on a pack. Battery replacement is a core operating cost, not a maintenance footnote - and nobody has a decade of real-world data on how fast these packs degrade under daily commercial punishment.

The pilot. The S4 carries a pilot, which is the honest and correct near-term plan for safety and certification. But the economic pitch - a ride costing about what a premium car service costs - leans on eventually removing that pilot. Autonomous flight is a separate, taller certification mountain. The near-term product is real; its business case sits on a future product that is much further away than the marketing implies.

Infrastructure. Air taxis need vertiports, chargers, and air-traffic integration into busy urban airspace. That isn’t Joby’s problem alone, which means it partly depends on cities and regulators moving at a speed they’re famous for not moving at.

The Honest Read (as of August 2026)

Joby is the closest thing this industry has to a real airplane on a real path. The aircraft works, the company has done the hard manufacturing homework, and it sits in the deepest part of the FAA process of anyone in the field. That is a lot - but “closest” is not “done.”

The last twenty percent of certification routinely takes longer than the first eighty, because that’s where every deferred hard question comes due at once. The next time a headline promises air taxis by next year, quietly ask which stage the company is in and whether the final rulebook is signed. The airplane will fly long before you can buy a ticket. Certification is the product; everything else is a demonstrator.

Key Takeaways

Joby’s S4 seats a pilot plus four passengers, uses six tilting propellers, cruises around 200 mph with roughly 100 miles of range, and is notably quiet at mid-40s decibels from ~2,000 feet.
FAA type certification runs in five stages; Joby is deep into stage four, but that is not the same as being certified.
The real bottleneck is “for credit” testing and the years spent negotiating airworthiness rules that didn’t previously exist for eVTOLs.
Backing from Toyota (over a billion dollars) and Delta, plus U.S. manufacturing in Marina, CA and Dayton, OH, signals serious execution - not just hype.
The biggest long-term risks are battery degradation, the eventual push toward pilotless flight, and urban infrastructure - and an overseas Dubai launch does not move the U.S. finish line.