Part 91 vs 121 vs 135: FAA Rules and Safety Ratings

Every flight in U.S. airspace follows the FAA's Part 91 rules. A flight you pay for has to meet a second, stricter set as well: Part 135 for on-demand charter and commuter flights, or Part 121 for the airlines. Knowing which applies tells you who is responsible for your flight and what standard it is held to.

The short answer: Part 91 covers private, non-commercial flying, such as an owner flying their own jet. Part 135 covers charter: the operator holds an FAA air carrier certificate and must meet stricter rules on pilots, crew rest, weather, maintenance and drug testing. Part 121 covers scheduled airlines, with the strictest rules of the three.

Part 91 vs 121 vs 135 at a glance

Sources: 14 CFR 91.1, 119.5, 120.1, 121.1, 121.436, 135.1, 135.243, 135.267 and 91.175. A simplified summary; the regulations have many conditions and exceptions.

Part 91: private flying

Part 91 is the baseline for everyone in U.S. airspace, from a student pilot in a Cessna 172 to an airline. On its own, it covers flights where nobody is paying for transportation: an owner flying their own aircraft, a company flying its executives in its own jet, a pilot taking friends along and sharing costs within strict limits.

Part 91 gives owners the most flexibility. There are no crew duty limits for private flights, no takeoff weather minimums, and the owner decides how to maintain the aircraft within the inspection rules. Many corporate flight departments hold themselves to much higher standards than the regulation requires, but nothing in Part 91 makes them.

What it means for you: if you are paying for a flight, it should not be flown under Part 91 alone. A private pilot may not act as pilot in command for compensation or hire, and an operator selling flights without a certificate is running an illegal charter.

Part 135: charter and air taxi

Part 135 governs commuter and on-demand operations, the rules every private jet charter must be flown under. To fly under Part 135, a company needs an FAA certificate and operations specifications that list its aircraft, its managers and what kinds of flights it may fly (14 CFR 119.5). On top of Part 91, Part 135 requires:

• More experienced pilots. The captain of a turbojet, or of an aircraft with ten or more passenger seats, must hold an airline transport pilot certificate; other captains flying on instruments need at least 1,200 hours (135.243). Pilots pass regular checks with the operator.
• Duty and rest limits. For unscheduled flights, a two-pilot crew may log up to 10 hours of flight time in 24 hours, and more only within a duty period of no more than 14 hours with at least 10 consecutive hours of rest before and after; quarterly and annual caps apply too (135.267).
• Weather minimums. Takeoff minimums apply, and an instrument approach needs an approved weather report at the destination.
• Drug and alcohol testing of crews and maintenance staff (Part 120).
• FAA oversight, with inspectors assigned to each certificate holder and its manuals, training and maintenance programs approved by the FAA.

The FAA lists 1,837 Part 135 certificate holders with 11,582 authorized aircraft on its legal Part 135 operators page.

Part 121: the airlines

Part 121 covers airlines flying scheduled domestic and international service and supplemental (charter) operations with larger aircraft. It has the strictest requirements of the three: both pilots must hold an airline transport pilot certificate with a type rating, and the captain needs at least 1,000 hours in airline-type operations (121.436); there are licensed dispatchers sharing operational control, flight attendants on larger aircraft and a continuous maintenance program. The ATP certificate itself normally requires 1,500 flight hours.

Private jets are almost never flown under Part 121. Some large charter operators of airliner-sized aircraft are certificated under it for supplemental operations.

How to check a charter operator

Whoever sells you a flight, the company that actually flies it must hold a Part 135 (or 121) certificate. To check:

1. Ask who operates the flight. A broker must tell you; U.S. rules require charter brokers to disclose the operating carrier. See broker versus operator.
2. Ask for the certificate number, the name on it and the aircraft's registration.
3. Look them up on the FAA's Part 135 operator list, updated weekly and searchable by operator or aircraft. The FAA's safe charter page explains what to look for, and its hotline for reporting suspected illegal charters is 1-866-835-5322.
4. Check the aircraft is on that operator's certificate, not just "managed by" it.
5. Ask about independent safety audits, below.

Safety ratings: ARGUS, Wyvern and IS-BAO

The FAA certificate is the legal minimum. Independent audit companies rate operators against stricter standards, and many corporate travel departments require one of these ratings before they book.

From each organization's own published descriptions, checked October 5, 2026.

A rating is a snapshot of an operator's systems at audit time, not a guarantee, and different travel departments trust different programs. It is still a strong signal: an operator that pays for an on-site audit and passes it has invited outside scrutiny that the FAA minimum does not require. Charter safety ratings goes into more detail.

How CRAFT operates

CRAFT is a Part 135 operator flying an all-Challenger 300 and 350 fleet, with Part 135 rules on every flight. CRAFT is ARGUS Platinum Rated and listed on the Wyvern registry, and has kept a clean safety record since 2020.

You can check both in the registries above, and read more about how we fly on our company page.