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Differences In Flying Regulations

PART 91

Part 91 is for general aviation, general operations and general flight rules.  It is the most unrestrictive form of flying.  Private aircraft owners or corporations that own their own aircraft may fly under Part 91.

Here are some things to know about flying under Part 91:

  • The flight cannot be operated for commercial purposes such as carrying passengers for hire.  This does not include being paid to fly an owner in their own aircraft.
  • The operators are not required to have any established safety programs.
  • There are no crew rest or duty day restrictions when flying under Part 91.
  • Weather minimums might be less restrictive such as being allowed to attempt takeoffs under zero-zero conditions.
  • Runway length determination is based only on the aircraft performance capabilities.
  • Crew training requirements are less stringent then Part 135 flying.

Flying under Part 91 is less restrictive but that does not mean it has to be less safe.  It is at the discretion of the pilots and operators to ensure safe operations. 

Part 91K 

Some companies or operators share an aircraft and fly under Part 91K. Part 91K covers Fractional operations and could include companies that manage aircraft as a business.

PART 121

Part 121 is known most for covering the regional and major airlines.  Air carriers authorized to operate under a Part 121 certificate are generally large, U.S.-based airlines, regional air carriers, and all cargo operators. Air carriers operate off of a planned schedule and they have to follow very strict safety and training standards.

PART 135

Part 135 includes on-demand or commuter charter operations that do not operate on a schedule like the airlines.  Most Helicopter operations also operate under Part 135.  These operations receive compensation for carrying passengers or cargo.  To operate under a 135 certificate, the FAA would have had to approve an Operations Specification (Ops Spec) that the company agrees to operate under. This Ops Spec outlines the specifics about the flight operations including specifics and differences in how they operate, their training, their checklists and even callouts.

On Demand – These are on-demand operations involving aircraft with 30 or less seats, a max payload of 7,500 lbs, or any rotorcraft.  They can conduct very limited scheduled operations.

Commuter – These are scheduled operations that involve aircraft with a max of 9 seats, a max payload of 7,500 lbs, or any rotorcraft.

Part 135 operations have more stringent requirements then Part 91 operations, such as:

  • They are required to have a management team supporting the operation (chief pilot, operations manager, etc).
  • They are required to have some kind of flight following since the company is in control of the operation, not the PIC.
  • The pilots are required to undergo specific training to fly with a specific Part 135 operation.  If the pilot leaves one part 135 company for another, flying the same aircraft, they will have to go back through training using the new companies SOPs.
  • There are much stricter crew rest rules, such as requiring 10 hours of rest in a 24 hour period preceding a flight.
  • They are required to have a strong Safety system implemented.
  • Their aircraft maintenance records are strictly regulated.
  • There are stricter weather requirements then Part 91 and different rules for runway lengths that can be used.

Other Important Parts to Know

PART 125

Part 125 covers large aircraft, 20+ passengers, operated by a corporation or individual, but not for general public travel. Think Menards, Cummins, or Donald Trumps 757.

PART 133

Part 133 covers Rotorcraft and external load operations.                                                        

PART 141

Part 141 covers flight schools that involve actual aircraft operations such as Embry-Riddle.

PART 142

Part 142 covers flight training facilities that operate Flight Simulators such as Flight Safety or CAE.