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Understanding the Federal Aviation Regulations: Part 91 vs. Part 135 vs. Part 121 vs. Part 380

The Federal Aviation Administration (FAA) sets forth various regulations that govern all aspects of civil aviation in the United States.

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These regulations are compiled in the Federal Aviation Regulations (FARs), which are part of Title 14 of the Code of Federal Regulations (CFR).

Among these, Parts 91, 135, 121, and 380 outline specific requirements and guidelines for different types of aviation operations.

Understanding the differences between FAR Parts 91, 135, 121, and 380 is essential for anyone involved in aviation, whether you’re a pilot, operator, or passenger.

Each part serves a distinct segment of the aviation industry, with specific regulations designed to ensure safety, efficiency, and compliance in various operational contexts.

From private flying to large-scale commercial airline operations, these regulations provide the framework that keeps the skies safe and orderly.

Let’s take a look at the key differences between these parts.

Part 91: General Operating and Flight Rules

Part 91 outlines the general operating and flight rules for all civil aircraft in the United States, covering a wide range of operations from private flying to business aviation.

Part 91 of the Federal Aviation Regulations (14 CFR 91) is a set of rules that govern non-commercial and general aviation operations in the United States, like a privately owned light plane like a Cessna 182, to luxury business jets flown with the owner on board, or corporate business jets carrying an executive team.

It applies to most small private aircraft that can be flown with a private pilot’s license, as well as civilian aircraft like private jets and luxury airliners.

These rules ensure safe and compliant operations by outlining requirements for pilots, aircraft maintenance, equipment, and flight.

Key Features of FAR Part 91

  • Applicability: Applies to private, non-commercial operations and corporate flight departments.
  • Maintenance: Requires aircraft to be maintained according to the manufacturer’s recommendations but is less stringent compared to commercial operations.
  • Pilot Certification: Pilots must hold at least a private pilot certificate, with specific ratings for the type of aircraft being flown. If the pilot is not the aircraft owner, they will also need a Commercial Pilot License if they are accepting any compensation to perform trips.
  • Operational Flexibility: Allows for greater flexibility in flight planning, including freedom from some of the more stringent commercial regulations.
  • Examples: Private flights by individuals, corporate flight departments, and fractional ownership programs.

Part 135: Commuter and On-Demand Operations

Part 135 regulates commercial operations involving private planes ranging from single and twin-engine light aircraft to long range business jets, and includes on-demand charter services (often known as air charter) and commuter operations (air taxi).

Federal Aviation Regulations Part 135 (14 CFR 135) sets the operating rules that the Federal Aviation Administration (FAA) requires for companies to operate as non-scheduled air charter carriers. The rules apply to operators, pilots, and the aircraft used, and are intended to ensure safe operations

Many Part 135 operators offer critical passenger and cargo service to remote areas, providing aviation services to populations that would not receive them otherwise.

Key Features of FAR Part 135:

  • Applicability: Applies to operators providing commercial air transportation of passengers or cargo for compensation or hire.
  • Maintenance: Requires adherence to a more rigorous maintenance program, often overseen by an FAA-approved maintenance provider.
  • Pilot Certification: Pilots must hold at least a commercial pilot certificate with appropriate ratings, and often an Airline Transport Pilot (ATP) certificate for captains.
  • Operational Restrictions: Includes more stringent operational rules, such as limitations on flight and duty time, specific weather minimums, and mandatory crew rest periods.
  • Examples: Charter services like the ones arrange for customers of Air Charter Advisors via part 135 operators, and commuter airlines operating smaller aircraft on scheduled routes.

Part 121: Scheduled Air Carrier Operations

Part 121 is the most comprehensive and stringent set of regulations, governing scheduled air carriers and large commercial operations.

Federal Aviation Regulations Part 121 (14 CFR 121) Certification allows a company to act as a scheduled airline. As a result, the air carrier may publish a schedule and is able to collect compensation for operating group charter flights.

Part 121 aircraft are approved to charter with 50+ passengers. These regulations are even more stringent than Part 135 (aircraft that can carry between 1-30 passengers) with regards to maintenance scheduling, runway length requirements, fuel reserves planning, pilot rest and duty day scheduling, and other factors for the sake of ensuring safe operations.

Single-engine airplanes are prohibited under this regulation, and no certificate holder may operate a single-engine airplane under this part.

Key Features of FAR Part 121:

  • Applicability: Applies to airlines operating scheduled flights with large aircraft (over 30 seats or a maximum payload capacity of more than 7,500 pounds).
  • Maintenance: Requires an extensive and continuous maintenance program with detailed record-keeping, often involving large maintenance facilities and teams.
  • Pilot Certification: Pilots must hold an ATP certificate and undergo regular recurrent training and proficiency checks.
  • Operational Stringency: Includes detailed regulations on virtually every aspect of operation, from flight crew qualifications and training to emergency procedures, passenger handling, and security measures.
  • Examples: Major airlines like Delta, United, and American Airlines.

Part 380: Public Charter Operations

Part 380 of the DOT’s regulations (14 CFR 380) requires all persons who wish to arrange public charter flights to first submit a charter prospectus to DOT which contains information about the proposed charter program.

Part 380 governs public charter operations, allowing charter operators to sell seats to the public on chartered flights, often for vacation packages or special events.

Key Features of DOT Part 380:

  • Applicability: Applies to both direct air carriers (airlines) and indirect air carriers (tour operators) that organize charter flights.
  • Regulatory Oversight: Requires filing a public charter prospectus with the Department of Transportation (DOT) detailing the terms of the charter, including prices, routes, and operational details.
  • Consumer Protections: Includes specific requirements to protect consumers, such as escrow of passenger payments and clear disclosure of terms and conditions.
  • Operational Requirements: While less stringent than Part 121, public charter operations must comply with many of the safety and operational standards applicable to the aircraft used, which are often operated under Part 121 or Part 135.
  • Examples: Vacation charters organized by tour operators, special event flights, and group travel arrangements.

More Information

For more details on the Federal Aviatoin Regulation governing private and public charter flights, as well as private jet memberships and and owner-operated aircraft, visit the FAA website: