Part 91, Part 135 and Part 121 are three sections of the federal aviation regulations, and together they decide what a pilot job looks like: who you fly, how many hours you need before anyone will let you, how long your duty day can be, and whether there is a seniority list at the end of it. If you are planning a flying career, they map the road from a new commercial certificate to an airline seat.
Quick Answer: Part 91 is the general operating rulebook every aircraft follows, and on its own it covers private flying, flight instruction and company flight departments. Part 135 adds the rules for charter and commuter operators, whose captains need at least 500 hours to fly by visual rules and 1,200 hours on instruments. Part 121 governs the airlines, where both pilots must hold an airline transport pilot certificate, which normally takes 1,500 hours.
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Three Rulebooks In One Paragraph
Think of them as layers. Part 91 applies to every civil aircraft in the country: right-of-way, weather minimums, equipment, altitudes. Part 135 sits on top of Part 91 for operators who carry passengers or cargo for hire on demand or on small scheduled routes, and it requires the operator to hold an FAA certificate and follow approved training, maintenance and crew rules. Part 121 sits on top of Part 91 for scheduled airlines and large charter operators, with the heaviest requirements of all. The deciding question is who is paying, for what, and in what size of airplane.
Part 91: General Operating Rules
Everything that is not a commercial air carrier operation happens under Part 91. That includes your own flying after a private pilot certificate, every lesson at a flight school like ours, ferry flights, and most aerial work: banner towing, aerial photography and pipeline patrol are all listed in 14 CFR 119.1(e) as operations outside the air carrier rules. It also includes corporate flight departments, where a company flies its own people in its own airplane on its own business and nobody buys a ticket.
A few specifics are worth knowing. Part 91 has no crew duty-time limits outside its fractional-ownership subpart (Subpart K, which has its own), so fatigue management rests with the pilot and the employer. Compensation is legal for a commercial pilot here, but the line that must not be crossed is carrying passengers or property for hire as if you were an airline or charter company. That is common carriage, and it needs a Part 119 operating certificate. We cover the line in detail in commercial pilot versus airline pilot and in commercial pilot privileges and limitations.
Part 135: Charter, Air Taxi And Commuter
Part 135 covers two kinds of work, as defined in 14 CFR 110.2. On-demand operations are charter and air taxi flights in aircraft with 30 or fewer passenger seats and a payload of 7,500 pounds or less. Commuter operations are scheduled flights, at least five round trips a week, in aircraft with nine or fewer passenger seats. Pilots fly for the certificate holder, which holds operational control of every flight.
The pilot-in-command minimums are in 14 CFR 135.243:
- VFR captain: at least a commercial pilot certificate; 500 hours as a pilot, including 100 hours of cross-country and 25 hours of night; and, for airplanes, an instrument rating or an airline transport pilot certificate.
- IFR captain: at least a commercial certificate with an instrument rating; 1,200 hours as a pilot, including 500 hours of cross-country, 100 hours of night and 75 hours of actual or simulated instrument time, at least 50 of them in flight.
- Larger aircraft: a turbojet, an airplane with ten or more passenger seats, or a multiengine airplane in commuter service needs a captain with an airline transport pilot certificate.
- Second in command: under 135.245, a commercial certificate with an instrument rating.
Duty limits are real here. For unscheduled one- and two-pilot crews, 14 CFR 135.267 caps flight time in any 24 consecutive hours at 8 hours for a single pilot and 10 hours for two, requires at least 10 consecutive hours of rest in the 24 hours before the planned end of an assignment, and requires 13 rest periods of at least 24 hours each calendar quarter.
Part 121: The Airlines
Part 121 covers domestic, flag and supplemental operations: scheduled flights in turbojets or in airplanes with more than nine passenger seats or more than 7,500 pounds of payload, plus large-aircraft charter. Regional and major airlines, and the big cargo carriers, all fly under it.
The certificate gate is the same in both seats. 14 CFR 121.436 requires the captain and the first officer to hold an airline transport pilot certificate and the aircraft type rating, and a captain also needs 1,000 hours as a Part 121 first officer or a listed equivalent. The certificate itself normally requires 1,500 hours of total time under 14 CFR 61.159, reduced under 61.160 to 750 hours for qualifying military pilots, 1,000 hours for graduates of qualifying aviation bachelor's programs, and 1,250 hours for some other degree holders. The detail, including what counts toward the total, is on the 1,500 hour rule and the restricted certificate.
Three more rules shape the job. Every Part 121 flight has at least two pilots (121.385(c)). No one may serve as a Part 121 pilot once they have reached their 65th birthday (121.383(d)). And for passenger operations, 14 CFR Part 117 requires at least 10 consecutive hours of rest, with an 8-hour uninterrupted sleep opportunity, before each flight duty period, and 30 consecutive hours free from duty in every 168 hours. Captains exercising airline transport pilot privileges need a first-class medical certificate.
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Side By Side
| Question | Part 91 | Part 135 | Part 121 |
|---|---|---|---|
| Who flies under it | Private pilots, flight instructors, corporate flight departments, aerial work, ferry | Charter, air taxi, air ambulance, small commuter routes | Regional and major airlines, large cargo carriers |
| Operator certificate | None for the operation itself | Part 119 certificate with Part 135 operations specifications | Part 119 air carrier certificate with Part 121 operations specifications |
| Minimum captain experience | Set by the certificate held and the insurer | 500 hours VFR; 1,200 hours IFR (135.243) | Airline transport pilot certificate plus 1,000 hours as a Part 121 first officer or equivalent (121.436) |
| Minimum first officer | Only where the aircraft or operation requires one | Commercial certificate with instrument rating (135.245) | Airline transport pilot certificate and type rating (121.436) |
| Duty and rest rules | None outside Subpart K | 135.267 and related sections | Part 117 for passenger flying |
| Age limit | None | None in Part 135 | 65 (121.383(d)) |
| Typical first job | Flight instructor at about 250 hours | First officer, or VFR captain from 500 hours | Regional first officer at 1,500 hours (or the reduced minimum) |
On pay, the federal data points the same way. The US Bureau of Labor Statistics put the May 2025 median for airline pilots, copilots and flight engineers at $232,140 a year, against $123,220 for commercial pilots overall and $133,150 for commercial pilots in nonscheduled air transportation, the industry that contains charter. The detail by job is on corporate and charter pilot pay and regional versus major airlines.
Where Each Fits In Your Career
The civilian route runs up the layers in order. You earn a commercial certificate at 250 hours (14 CFR 61.129), usually with an instrument rating, and then most pilots add the flight instructor certificate, because instructing under Part 91 is the fastest paid way to build hours. At 500 hours, VFR charter captain jobs open; at 1,200 hours with the right cross-country, night and instrument time, IFR charter; at 1,500 hours, the airline transport pilot certificate and a Part 121 first officer seat. Some pilots stay in Part 135 or corporate flying for a whole career by choice. The jobs in between are covered on time-building jobs for commercial pilots.
At Van Nuys our Airline Pilot Career Program takes a student with no experience through Private, Instrument, Commercial single and multi-engine, CFI, CFII and MEI in about nine months and 260 logged hours for a fixed $82,000, with a guaranteed paid flight instructor job at $48,000 a year while you build toward 1,500 hours, and a guaranteed airline interview. If you already hold a private certificate, the Commercial Pilot course is $15,900 and the CFI, CFII and MEI program is $15,900.
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Frequently Asked Questions
Does Part 135 Or Part 121 Pay More?
As a rule, Part 121. The May 2025 BLS median for airline pilots was $232,140, against $133,150 for commercial pilots in nonscheduled air transportation. Individual Part 135 jobs flying large business jets can pay very well, and a first-year regional first officer can earn less than an experienced charter captain, so compare specific offers rather than averages.
Which Is Safer, Part 91, 135 Or 121?
The requirements rise with each layer: more training and checking, operator control of every flight, dispatch or flight-following, duty limits and, at Part 121, two pilots on every flight. That extra structure is the reason scheduled airline flying is held to the highest standard in US aviation. A well-run Part 91 or 135 operation can be very safe, but the rules guarantee less.
Can A Flight Instructor Fly Part 135?
Yes, once they meet the operator's minimums and those in 135.243 or 135.245. The flight instructor certificate itself adds nothing for Part 135; what matters is the commercial certificate, the instrument rating and the logged hours. Many instructors move to charter at 500 or 1,200 hours.
Is Flight Training Part 91 Or Part 141?
Both, in different senses. Part 61 and Part 141 set how training is structured and certified, while the flights themselves are operated under Part 91. Student instruction is one of the operations 119.1(e) places outside the air carrier rules.
Can I Get A Part 135 Job At 250 Hours?
Occasionally, as a second in command where an operator's aircraft or operation calls for one, which needs a commercial certificate and instrument rating under 135.245. Most operators also set their own higher minimums and their insurers set theirs. VFR captain work begins at 500 hours.
Do Cargo Airlines Fly Under Part 121?
The large ones do, under the same certificate and pilot qualification rules as passenger airlines, including the airline transport pilot requirement in 121.436. Part 117's flight and rest limits are written for passenger operations; an all-cargo carrier may elect to fly under Part 117 (117.1(d)) or stay with the older Part 121 flight-time rules. Small feeder cargo flying is often Part 135.
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Sources: 14 CFR 61.23, 61.129, 61.159 and 61.160; 14 CFR 110.2 (definitions of commuter, on-demand, domestic, flag and supplemental operations); 14 CFR 119.1(e); 14 CFR 121.383, 121.385 and 121.436; 14 CFR 117.1 and 117.25; 14 CFR 135.243, 135.245 and 135.267; 14 CFR Part 91, Subpart K; US Bureau of Labor Statistics, Occupational Outlook Handbook, Airline and Commercial Pilots (May 2025 wages).
