The Core Distinction: Who Pays for the Flight
The FAA's Federal Aviation Regulations divide private aviation into regulatory parts based on one question: is the flight being conducted for compensation or hire? Part 91 governs flights where the aircraft owner or operator bears the cost. Part 135 governs flights where a third party pays for the transportation. As of Q1 2026, the FAA maintains approximately 2,100 active Part 135 Air Carrier Certificates in the United States.
When you own an aircraft and fly yourself, your family, or your employees on company business, that flight operates under Part 91. When you call a charter broker and pay an operator to fly you, that operator must hold a Part 135 certificate and the flight operates under Part 135 regulations. The distinction is not about aircraft type, airport, or flight distance. It is entirely about the commercial relationship.
2,100+
Active Part 135 Certificates
1,500 hrs
PIC Minimum (Part 135)
100-hr
Inspection Interval (135)
Pilot Requirements: 250 Hours vs. 1,500 Hours
The most consequential difference between Part 91 and Part 135 is pilot qualification minimums. Part 91 requires only that the pilot-in-command hold the appropriate certificate and ratings for the aircraft and flight conditions. A private pilot with 250 total flight hours and an instrument rating can legally fly a turbine aircraft under Part 91 if they hold the appropriate type rating.
Part 135 imposes substantially higher minimums. The pilot-in-command must hold an Airline Transport Pilot (ATP) certificate, which requires a minimum of 1,500 total flight hours, including 500 hours of cross-country time and 100 hours of night time. For IFR operations (which constitute virtually all Part 135 flights), the PIC must have logged 1,200 hours total with 500 hours of actual instrument time. Second-in-command pilots must hold at least a commercial pilot certificate with 500 total hours.
Beyond the hour minimums, Part 135 mandates initial and recurrent training programs administered by the certificate holder. Pilots must complete ground school, simulator training, and line checks before operating revenue flights. Annual proficiency checks (checkrides) are required by the FAA, and many operators impose semi-annual checks as a matter of company policy. Part 91 requires only a biennial flight review (BFR) every 24 months.
The 1,250-hour experience gap between Part 91 minimums (250 hours) and Part 135 minimums (1,500 hours) is the single largest safety differential in private aviation. It is the reason charter operations under Part 135 have a materially different accident rate than owner-flown Part 91 operations. Experience does not prevent every accident. But it prevents most of the avoidable ones.
Maintenance: Annual Inspections vs. 100-Hour Programs
Part 91 requires an annual inspection of the aircraft by an authorized inspector (IA) or certified repair station. Between annuals, the owner bears responsibility for airworthiness, but no mandatory inspection interval exists. An aircraft can fly 800 hours between annuals without a required maintenance event beyond the owner's discretion.
Part 135 requires 100-hour inspections for aircraft used in revenue service. Every 100 flight hours, the aircraft must undergo a detailed inspection equivalent in scope to an annual inspection. Additionally, Part 135 operators must maintain a Continuous Airworthiness Maintenance Program (CAMP) or follow an approved inspection program that often exceeds the 100-hour requirement. Most Part 135 operators operating modern turbine aircraft subscribe to manufacturer-approved maintenance tracking programs that mandate inspections at specific hour and calendar intervals.
| Requirement | Part 91 (Private) | Part 135 (Charter) |
|---|
| PIC Minimum Hours | 250 (with ratings) | 1,500 (ATP required) |
| Recurrent Training | Biennial flight review | Annual checkride + ground school |
| Maintenance Inspection | Annual | 100-hour + CAMP program |
| Liability Insurance | No federal minimum | $50M-$500M typical |
| Drug/Alcohol Testing | Not required | FAA-mandated program |
| Duty Time Limits | None | 14 hr duty / 10 hr flight |
| Operational Control | Pilot/owner | Certificate holder |
| Flight Following | Not required | Required by most ops specs |
| MEL Compliance | Permissive deferral | Approved MEL required |
| Passenger Compensation | Not permitted | Revenue flights authorized |
The practical result: a Part 135 charter aircraft receives approximately 4-8 times more mandated maintenance oversight per year than a comparable Part 91 aircraft flying the same number of hours. This is not discretionary. The certificate holder's Operations Specifications define the maintenance program, and FAA inspectors audit compliance.
Verify Your Operator's Certificate
Every flight we arrange operates under a valid Part 135 certificate. We verify operator status, insurance, and safety ratings before presenting options.
Contact Us →Insurance: The Gap Most Passengers Never See
Part 91 has no federal minimum insurance requirement. An aircraft owner can legally operate with zero liability insurance, though lenders and hangar owners typically require coverage as a condition of financing or facility use. In practice, most Part 91 operators carry $1M-$5M in liability coverage per occurrence.
Part 135 operators must carry liability insurance as a condition of their certificate. While the FAA does not specify a dollar minimum in the regulation, the practical requirements imposed by charter brokers, airport authorities, and the market establish de facto minimums. Most Part 135 operators carry $50M-$200M in combined single-limit liability insurance. Large operators on heavy jets carry $250M-$500M. This coverage protects passengers, crew, and third parties.
The insurance gap matters because it defines the financial recourse available if something goes wrong. A Part 91 flight operated by a thinly capitalized owner with $1M in coverage and no excess umbrella policy provides fundamentally different passenger protection than a Part 135 flight operated by a certificate holder with $100M in coverage, a drug testing program, and an audited safety management system.
Operational Control: Who Decides If the Flight Happens
Part 135 assigns 'operational control' to the certificate holder. The operator, not the passenger, decides whether conditions are safe enough to fly. The Director of Operations evaluates weather, crew duty time, aircraft maintenance status, and route considerations. A passenger who has paid for a charter flight cannot override the operator's decision to delay or cancel for safety reasons.
Part 91 assigns operational control to the pilot-in-command. On an owner-flown aircraft, the owner is both the financial decision-maker and the safety decision-maker. This dual role creates pressure that does not exist under Part 135: the owner who needs to be in Chicago by 3 PM is also the person deciding whether to depart into deteriorating weather. The separation of financial interest from safety authority is a foundational principle of Part 135 that Part 91 does not require.
- Drug and alcohol testing: Part 135 operators must maintain an FAA-approved anti-drug and alcohol misuse prevention program. All crew members undergo pre-employment, random, post-accident, and reasonable-suspicion testing. Part 91 has no drug or alcohol testing requirement.
- Crew duty time limits: Part 135 restricts pilot duty time to 14 hours and flight time to 10 hours in any 24-hour period. Minimum rest between duty periods is 10 consecutive hours. Part 91 imposes no duty time limits beyond the pilot's own judgment.
- Dispatch and flight following: Most Part 135 operators maintain a dispatch or flight-following system that monitors aircraft position, weather conditions, and crew status in real time. Part 91 does not require flight following beyond ATC communication.
- MEL (Minimum Equipment List): Part 135 aircraft must operate in accordance with an approved MEL that defines which equipment failures are acceptable for dispatch. Part 91 aircraft may defer equipment inoperative items under more permissive rules.
The Gray Market: Part 91 Flights Sold as Charter
The most significant regulatory risk in private aviation involves Part 91 aircraft being operated for compensation without a Part 135 certificate. This is commonly called 'gray market' or 'illegal charter.' An owner who rents their aircraft to a third party for a weekend trip, a management company that places an aircraft on charter without the owner's approved 135 certificate, or a broker who arranges flights on non-certificated aircraft are all operating outside FAA regulations.
Gray market flights are illegal. The FAA pursues enforcement actions against operators, management companies, and in some cases brokers who facilitate uncertificated charter operations. More importantly for passengers: gray market flights operate without the pilot qualification requirements, maintenance programs, insurance minimums, drug testing, and operational controls that Part 135 mandates. In the event of an accident, insurance coverage may be voided entirely if the flight is determined to have been conducted illegally under Part 91 when it should have been Part 135.
Ask your broker one question before confirming any charter: 'Who holds the Part 135 certificate for this flight, and what is their certificate number?' A legitimate broker answers immediately. If the answer is vague, conditional, or involves explanations about Part 91 'dry leases' or 'time-sharing agreements,' you are likely being offered a gray market flight. Walk away.
