Ask most charter clients who’s actually responsible for the safety standards on their flight, and you’ll get a shrug. Most people assume every private jet flies under the same rules. It doesn’t. Two completely different sections of the Federal Aviation Regulations govern that flight. One dictates how experienced your pilot must be and how much rest they need. The other decides how closely the FAA inspects the aircraft you’re sitting in. Knowing the difference between Part 91 and Part 135 tells you a lot about what you’re actually buying when you book a flight.
The Basic Split
FAR Part 91 covers general operating rules, the framework for private, non-commercial flying. If you own an aircraft or fly on one through a fractional program, you’re typically operating under Part 91. FAR Part 135, by contrast, governs on-demand commercial charter. Any operator selling you a seat or a trip for compensation, whether that’s a broker-arranged charter or a jet card flight, needs a Part 135 certificate to do it legally.
The distinction sounds bureaucratic. It isn’t. It changes who inspects the aircraft, how experienced your pilots must be, and how much operational cushion exists if weather turns or a runway gets short.
Where the Rules Actually Diverge
Part 135 exists because the FAA treats paid transportation as a higher-stakes activity than an owner flying their own aircraft. The oversight reflects that.
- Pilot experience: Part 135 captains face recurring FAA-mandated proficiency checks every six months. Part 91 owner-flown pilots face no such regulatory requirement, though many still complete annual training voluntarily through programs like FlightSafety or CAE, often driven by insurance requirements rather than any FAA mandate.
- Runway safety margins: Part 135 operators must be able to land within 60% of the available runway at the destination, per FAR 135.385, which in practice means longer runways than raw aircraft performance numbers alone would require. Part 91 operators have more discretion here.
- Maintenance oversight: Part 135 aircraft fall under an FAA-approved maintenance program with tighter inspection intervals and record-keeping the agency actively audits.
- Duty and rest rules: Charter pilots operate under stricter flight time and rest requirements designed around commercial-style scheduling pressure.
- Drug and alcohol testing: Mandatory random testing programs apply to Part 135 crews, not universally to Part 91 owner-flown operations.
A Side-by-Side Look
| Factor | Part 91 | Part 135 |
|---|---|---|
| Who uses it | Owners, fractional programs | Charter operators, jet card providers |
| Pilot proficiency checks | No FAA mandate; often voluntary/insurance-driven | FAA-mandated every 6 months |
| Landing distance margin | Aircraft performance limit | Must land within 60% of available runway |
| Maintenance program | Manufacturer-recommended | FAA-approved and audited |
Why This Matters When You’re Booking a Flight
Here’s the part that catches people off guard: a Part 91 flight isn’t necessarily less safe. Many owner-flown Gulfstreams and Global jets are operated by professional crews holding standards that meet or beat Part 135 minimums. But you have no regulatory guarantee of that under Part 91, because the FAA doesn’t require it. Part 135 exists precisely because the passenger paying for a seat has no way to vet the operator’s internal standards themselves. The rule fills that gap.
This is also why wet lease and dry lease arrangements get scrutinized so closely by aviation attorneys. A dry-leased aircraft flown by the lessee’s own crew usually stays under Part 91. Add a crew supplied by the aircraft owner and you can trip into Part 135 territory, whether or not anyone intended it. The FAA has pursued enforcement action against operators who blurred that line, often called illegal or “gray” charter.
The Pilot’s Side of the Equation
For working pilots, the two rulebooks shape entire careers differently. A Part 135 captain answers to duty limits that cap how long they can sit in the seat on a given day, a topic worth understanding in more depth through how pilot duty limits actually work. Combine that with the reality that the pilot in command holds final authority regardless of which regulation applies, and you start to see how much structure sits behind a flight that, from the cabin, looks effortless.
Runway performance is where the practical difference shows up most. A Part 135 charter into a shorter regional airport might get turned down, or require a smaller aircraft, purely because of the mandated safety margin. A Part 91 owner flying the same aircraft into the same runway may have more latitude, assuming the crew and operations manual support it. Neither approach is reckless. They’re just built around different assumptions about who’s flying and why.
What This Means Going Forward
The FAA’s ongoing gray-charter enforcement actions, referenced above, suggest this scrutiny isn’t going away as the charter and jet card markets keep growing. Before your next trip, ask the operator for their Part 135 certificate number and confirm it against the FAA registry yourself. It takes less time than boarding, and it tells you exactly what safety net sits underneath your flight.