Part 91 vs. Part 135: Which Rules Is Your Charter Flight Really Flying Under?

The difference isn't paperwork. It's who is responsible for your flight and which safety rules they have to meet.

Founder & President, Jet Mentis Partners. Director of Operations for a Part 135 charter operator, FAA Check Airman, 20+ years in on-demand charter.

Executive summary

Part 91 and Part 135 are two different sets of FAA rules, and which one a flight falls under is not a matter of choice or paperwork. Part 91 covers private flying, where the owner or operator is not selling transportation. Once someone pays to be flown, the flight almost always has to be conducted by an operator holding an FAA Part 135 certificate. That certificate brings tougher rules on pilot experience and recurrent checks, crew duty and rest, maintenance, drug and alcohol testing, and FAA oversight. The quickest test for any trip: who has operational control, and does that company hold a Part 135 certificate that covers this aircraft?

What is the difference between Part 91 and Part 135?

Both are parts of Title 14 of the Code of Federal Regulations, the FAA's rulebook.

• Part 91 is the general operating rules every aircraft in the U.S. follows. On its own, it covers flying that isn't being sold: an owner flying himself and his guests, or a company flying its own people on company business.
• Part 135 is the set of rules for commuter and on-demand operations, which is what most people mean by "charter." A company can't simply decide to follow it. It has to apply to the FAA, prove it can meet the rules, and receive an operating certificate and Operations Specifications (OpSpecs) that list exactly what it is authorized to do and with which aircraft.

The aircraft can be identical. A King Air flown privately by its owner on Saturday can be flown on a Part 135 charter on Monday. What changes is who is responsible for the flight and which rules apply to them.

When does a flight have to be Part 135?

The FAA's test is called common carriage. Under FAA Advisory Circular 120-12A, it has four elements:

1. Holding out a willingness to
2. transport persons or property
3. from place to place
4. for compensation.

When all four are present, an operating certificate is required, whatever the paperwork calls the arrangement.

Two points catch people out:

• Holding out doesn't need an advertisement. The advisory circular counts a reputation for serving whoever asks, and holding out through agents. In practice, word of mouth or a broker passing an aircraft along to clients can be enough.
• Compensation doesn't require a profit. The FAA's legal interpretations treat almost any payment or benefit as compensation. "The client just covers my fuel and my pilot" is still compensation. Money that only covers cost still counts.

In plain English: if a passenger is paying for transportation, the flight should be conducted by a properly authorized Part 135 operator, unless one of a few narrow exceptions genuinely applies.

Aren't there legal ways to share costs under Part 91?

Yes, and they are narrower than most people think.

• Time-sharing agreements (14 CFR 91.501). An owner of an eligible airplane (one over 12,500 pounds maximum certificated takeoff weight, or a multiengine turbojet) can be reimbursed for specific listed costs: fuel (up to twice its cost), crew travel expenses, hangar and tie-down costs away from base, landing fees, flight-specific insurance, catering and a few others. The list does not include a pilot's day rate or the airplane's fixed costs. Where the truth-in-leasing rule applies, the paperwork has to meet it, and the arrangement is not something a broker sells to the public.
• Other Part 91 Subpart F arrangements such as interchange and joint ownership, each with its own conditions.
• Private pilots sharing expenses with passengers under 14 CFR 61.113. The pilot may not pay less than the pro rata share of fuel, oil, airport expenses or rental fees, the FAA expects a common purpose for the trip, and it is not a way to sell a flight.

None of these is a back door to charter. If you are being offered a trip, quoted a price and asked to pay, assume it needs to be on a Part 135 certificate until someone shows you otherwise in writing.

What do you actually get with a Part 135 operator?

This is the part that matters to the person in the back of the airplane. A Part 135 operator has to meet requirements a private Part 91 flight does not, including:

• Pilot experience minimums and recurrent checks. Pilots must meet experience requirements (14 CFR 135.243) and pass regular competency, instrument and line checks (135.293, 135.297, 135.299).
• Crew flight-time and rest limits. For most charter crews, flight time is capped at 8 hours for a single pilot or 10 hours for two pilots in any 24 hours, and each crewmember needs at least 10 consecutive hours of rest in the 24 hours before an assignment ends (135.267). In practice that works out to about a 14-hour duty day.
• Maintenance programs that go beyond the basic Part 91 inspections.
• Drug and alcohol testing for safety-sensitive employees (14 CFR Part 120).
• Operational control held by named, FAA-accepted managers, with the FAA overseeing the operation.
• Insurance and DOT registration. On-demand air taxi operators register with the Department of Transportation and carry liability insurance that meets federal minimums.

A Part 91 flight can be flown by excellent pilots on a beautifully maintained aircraft. The point is that nobody is required to prove it, and nobody is overseeing it as a commercial operation. That is the difference you are paying for.

How do I check whether my charter is really Part 135?

Ask three questions before you pay, and expect clear answers:

1. Who is the operator? You should get the legal name of the company that holds the certificate and has operational control. Not a brand name, not a management company, not "our partner."
2. Is this aircraft on their certificate? Ask for the operator's OpSpecs A001 (which names the certificate holder) and D085 (which lists the aircraft by registration number).
3. What insurance covers the trip? Ask for a current certificate of insurance.

If you are working with a charter broker, the broker is required by the DOT's broker rule (14 CFR Part 295) to tell you which operator is providing the aircraft before you sign. A broker who can't or won't name the operator is a broker to walk away from.

The two-question test

I ask two questions about every flight: Is it safe? Is it legal? Just because a trip is safe doesn't make it legal, and just because it's legal doesn't make it safe. Part 135 is how the FAA makes sure the second answer is yes, and it goes a long way toward the first.

Starting or running a charter operation? Jet Mentis Partners helps operators through FAA Part 135 certification and the compliance work that comes after it. New to charter brokerage? The Jet Mentis Charter Foundation opens for enrollment November 1, 2026, and teaches this from the ground up. Learn more at jetmentis.com.

This article is general education, not legal advice. Regulations change; check the current text at ecfr.gov, and talk to an aviation attorney about your specific situation.