Part 91 vs Part 135 — What the Difference Means for Your Flight

Aviation regulations have gotten complicated with all the gray-area marketing and vague operator language flying around. As someone who spent several years working adjacent to charter operations — first coordinating ground crews, then helping a small FBO wrestle with scheduling and compliance paperwork — I learned everything there is to know about what separates a legitimate charter flight from something that only looks like one. Most people booking a private flight genuinely have no idea which rulebook governs their trip. The industry doesn’t exactly rush to explain it.

This is my attempt to fix that. Whether you’re writing a check for your first charter or you just cracked open the FAR/AIM and found yourself staring at a wall of federal numbering that means nothing yet — this one’s for you. We’ll keep the legal language lean and focus on what actually happens on the ramp, in the cockpit, and to your safety.

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Part 91 vs Part 135 in Plain English

Title 14 of the Code of Federal Regulations — pilots just call it the FARs — organizes aviation rules into numbered parts. Part 91 covers general operating and flight rules. Part 135 covers on-demand and commuter operations, which is the legal home of charter flying. They are not interchangeable, and the gap between them is bigger than most passengers realize.

What Part 91 Actually Covers

But what is Part 91? In essence, it’s the baseline ruleset for almost every aircraft operating in U.S. airspace. But it’s much more than that — it’s the framework governing private flying in all its forms. The weekend pilot taking his Cessna 172 up on a Saturday morning. The corporate flight department moving executives around in a Gulfstream G550. The flight school running Piper Archers in the pattern at lunch. Under Part 91, the owner or operator is flying for their own purposes — no compensation, no hire.

The rules are less stringent here because the assumption is that whoever accepts the risk also chose to take it. Your airplane. Your call on airworthiness. Your judgment on conditions. The FAA sets minimums, but private operators have considerably more latitude than commercial ones do. For a private pilot flying his own aircraft, that makes complete sense — he’s an informed participant accepting personal risk. The rules reflect exactly that.

Where Part 135 Comes In

The moment someone pays for that flight, everything changes. Part 135 exists to protect paying passengers — people who aren’t aviation professionals, who can’t evaluate whether an aircraft is airworthy, and who are trusting a stranger’s operation with their lives. That’s a fundamentally different situation, and the FAA treats it accordingly.

Under Part 135, an operator must hold an Air Carrier Certificate issued by the FAA. Getting that certificate is not a weekend project. It requires submitting a full operations manual, demonstrating adequate maintenance programs, proving qualified personnel are in place, and passing FAA inspection. The whole process typically runs six to twelve months for a new operator and costs tens of thousands of dollars to complete properly. A single-pilot, single-aircraft charter operation running a Pilatus PC-12 out of a regional airport still needs one — airline-size assumptions don’t apply here.

The key operational differences under Part 135 include:

• Pilots must meet higher minimums — a Part 135 captain flying single-pilot IFR needs at least 1,200 hours total time, 500 hours cross-country, 100 hours actual instrument time, and 25 hours in the specific make and model
• Aircraft must undergo more rigorous maintenance inspections, including 100-hour inspections that Part 91 simply doesn’t require
• Operators must have FAA-reviewed and approved maintenance programs
• Flight and duty time limitations apply — hard caps on how long pilots can fly before mandatory rest, with no Part 91 equivalent
• Aircraft must meet higher airworthiness standards, including specific equipment requirements tied to the type of operation
• Operators must carry minimum insurance coverage levels as specified in their operating certificate

None of those requirements exist in Part 91 private operations. They exist in Part 135 because passengers have no other protection. That’s the whole point.

What This Means If You Are Chartering a Flight

Probably should have opened with this section, honestly. If you’re the one writing the check, everything that follows is the part that directly affects you.

When you book a charter flight, you should be flying under Part 135. Full stop. If someone is selling you a seat on an aircraft without holding a Part 135 certificate, you are in an illegal operation — and more to the point, you’re in an operation that has bypassed every safety standard the FAA built specifically to protect people in your seat.

The Pilot Flying Your Charter

Under Part 135, the pilots on your flight have met verified minimums. The FAA doesn’t just take the operator’s word for it — pilot records, logbooks, training certificates, and medical certificates are all subject to inspection during surveillance visits. The operator’s chief pilot has personally approved those pilots to fly specific equipment. Currency requirements are tracked and documented, not estimated.

Under Part 91 private operations, a pilot needs a valid medical and a current flight review — a biennial two-hour session with an instructor — to legally fly. That’s it. A pilot with 300 total hours and a private certificate can legally take his friends up in his Beechcraft Bonanza A36. Entirely legal. Potentially unwise depending on conditions, but the FAA cannot stop him from making that call for himself and his passengers.

Don’t make my mistake. I once accepted a discounted flight with someone who described himself as running a “private air transport” service out of a small field in central Virginia — he was operating his Piper Malibu under Part 91, taking money under a gray-area timeshare arrangement that skirted legality by maybe half an inch. The airplane had a cylinder running rough for weeks. I only found out afterward. He hadn’t addressed it because, operating under Part 91, nobody was checking. That’s the difference — real money, and I ended up in an airplane I would never have boarded had I spent fifteen minutes asking the right questions first.

The Aircraft Itself

Part 135 aircraft comply with maintenance schedules reviewed and approved by the FAA. Most legitimate operators use computerized maintenance tracking — companies like Traxxall or CAMP (Continuous Airworthiness Monitoring Program) — to track every squawk, every component life limit, every inspection interval. The FAA’s principal maintenance inspector for that certificate holder can walk in on any given Tuesday and pull those records.

A Part 135 operator flying a Citation CJ3+ runs a maintenance program that specifies exactly when every component gets inspected, replaced, or overhauled. The engines — Williams FJ44s in that aircraft — have tracked life limits down to the cycle. Nothing gets deferred without documentation and, in many cases, without FAA approval.

Compare that to a privately owned aircraft under Part 91, where the annual inspection is the primary safety gate. One thorough annual per year. Everything else runs on the owner’s judgment and his mechanic’s recommendations. For a careful owner with a well-maintained airplane, that can be entirely sufficient. For a charter passenger with no ability to evaluate the aircraft before boarding, it’s not a system built to protect you.

Insurance and Liability

Legitimate Part 135 operators carry substantial liability coverage — typically a minimum of $1 million per seat, often considerably higher. That coverage is a condition of their operating certificate, not a voluntary choice.

An individual flying under Part 91 may carry anywhere from $100,000 to whatever their personal policy covers. Some owners carry very little. If that flight ends badly, the path to meaningful compensation for a passenger is far less clear — and far less certain.

When you’re comparing charter quotes and one operator comes in noticeably cheaper than everyone else, the right question isn’t “why are they so affordable?” The right question is: “Are they actually Part 135 certificated?” Ask to see their operating certificate number and verify it in the FAA’s CAROL database. Takes about ninety seconds. Worth doing every single time.

Part 121 — How Airlines Are Different From Both

To complete the picture, you need one more number. Part 121 governs scheduled air carrier operations — Delta, United, Southwest, every other scheduled commercial airline. It is the most stringent tier of the three, by a meaningful margin.

The Three-Tier System

Think of it as concentric circles of regulatory oversight:

1. Part 91 — private operations, most training, corporate aviation. The baseline. Flexible, personal accountability, minimal third-party oversight of day-to-day decisions.
2. Part 135 — charter, on-demand, and commuter operations under 30 seats. Significantly elevated requirements. FAA-certificated operator with approved manuals, programs, and ongoing surveillance.
3. Part 121 — scheduled airline service. The highest standard. Crew resource management requirements, first officer minimums of 1,500 total hours, mandatory rest rules revised under the 2013 fatigue rulemaking, simulator training measured in dozens of hours per crew member per year.

The Boeing 737-800 departing gate C22 at 7:05 AM on United has two pilots who each completed type rating training in a full-motion Level D simulator — a box that costs roughly $20 million to build and around $2,000 to $3,000 per hour to operate. Their training records go back years. Their fatigue status was calculated before dispatch. The aircraft has maintenance records going back to the day it rolled out of Renton, Washington. Part 135 is rigorous. Part 121 is another tier beyond that entirely.

Why Charter Isn’t Airline Service — and That’s Fine

That’s what makes properly operated Part 135 charter endearing to us as aviation consumers — it occupies a genuinely useful middle ground. It’s not trying to be an airline. The accident statistics for legitimate Part 135 operators bear out that the system works. The point isn’t that charter is unsafe. The point is that these regulatory tiers exist for reasons grounded in operational reality, and understanding them helps you make smarter decisions — both as a consumer and as a pilot.

A Bombardier Challenger 350 flown by a legitimate Part 135 operator — two properly qualified pilots, current training records, maintained airworthiness program — is a safe, well-regulated product. The rules around it were written to make it that way. What the rules cannot do is protect you from an illegal operation masquerading as something it isn’t. That protection has to come from you, and it takes about two minutes of due diligence before you board.

A Final Note for Student Pilots

If you’re a student or low-time pilot reading this while trying to figure out where you fit into the regulatory landscape — you’re in Part 91. When you’ve built enough hours and ratings to fly charter, Part 135 will become your world, and its requirements will start shaping your training goals in very concrete ways.

The 1,200-hour IFR captain minimum under Part 135 single-pilot operations isn’t an arbitrary hurdle someone invented to be difficult. It represents a reasoned judgment about the experience level needed to manage a complex aircraft, an instrument environment, and passenger responsibility — simultaneously, on a bad day, in real conditions.

Understanding why these rules exist — not just what they say — makes you a sharper pilot and a more informed participant in the system. Start with Part 91. Respect what Part 135 represents. And when you eventually fly for hire, carry the obligation that comes with it like it actually means something. Because it does.