What are the regulatory categories of aircraft defined by the FAA?
The FAA defines several different types of aircraft, which have different applicable regulations. For fixed-wing aircraft, airworthiness for normal, utility, acrobatic, and commuter categories is covered in Part 23.
Note: Seat number excludes pilot seats. Weights are maximum certificated takeoff weights.


Normal category

Seats: 9 or less
Weight: 12,500 lb or less
Allowed maneuvers:

Any maneuver incident to normal flying;
Stalls (except whip stalls); and
Lazy eights, chandelles, and steep turns, angle of bank 60 degrees or less


Utility category

Seats: 9 or less
Weight: 12,500 lb or less
Allowed maneuvers:

Normal category, plus:
Spins (if approved for the particular type of airplane); and
Lazy eights, chandelles, and steep turns, or similar maneuvers, angle of bank can be more than 60 degrees but not more than 90 degrees


Acrobatic category

Seats: 9 or less
Weight: 12,500 lb or less
Allowed maneuvers:

Anything not prohibited due to flight tests


Commuter category

Seats: 19 or less
Weight: 19,000 lb or less
Engines: 2 or more
Allowed maneuvers:

Any maneuver incident to normal flying;
Stalls (except whip stalls); and
Steep turns, angle of bank 60 degrees or less





  Except for commuter category, airplanes may be type certificated in more than one category if the requirements of each requested category are met.


Beyond commuter category, there is the transport category. Multi-engine airplanes satisfying either of the below requirements must be certified in this category. Airworthiness for the transport category is covered in Part 25.


Transport category

Seats: 20 or more
Weight: more than 19,000 lb





For rotorcraft, there are two main categories: normal and transport. Airworthiness for the normal category is covered in Part 27.


Normal category

Seats: 9 or less
Weight: 7,000 lb or less



Multi-engine rotorcraft satisfying these conditions may be certified under transport Category A (see below) if they satisfy certain conditions.

Airworthiness for the transport category is covered in Part 29. There are sub-categories here as well.


Transport category

Category A

Seats: 10 or more
Weight: more than 20,000 lb

Category B

Seats: 9 or less
Weight: 20,000 lb or less




If a rotorcraft only satisfies one of the requirements for Category A, it may be certificated under Category B with certain additional requirements.


  A multiengine rotorcraft may be type certificated as both Category A and Category B with appropriate and different operating limitations for each category.




There is also a manned free balloon category covered in Part 31. 


  A balloon is a lighter-than-air aircraft that is not engine driven, and that sustains flight through the use of either gas buoyancy or an airborne heater.




Part 21 addresses the certification process itself, and includes special types of certificates for other aircraft.


Primary category

Power sources allowed:

None
Single naturally aspirated engine (stall speed 61 kt or less)
Rotorcraft with 6 lb per square foot main rotor discs loading limitation (sea level standard day)

Weight: 2,700 lb or less (seaplanes 3,375 or less)
Seats: 3 or less
Unpressurized



The restricted category allows a plane to not meet certain requirements under the normal regulations. The aircraft must meet one of the following conditions:


Restricted category

Requirements of any regular category, except any that are "inappropriate" for the aircraft's purpose
Armed Forces aircraft modified for a special purpose



US Armed Forces surplus aircraft can also be certified under one of the below conditions. The FAA has some leeway to waive requirements or add additional ones.


Surplus aircraft of the Armed Forces

Designed and constructed in the US, satisfies certain regulations
Counterpart of previously certified civil aircraft, complies with those regulations





Special certificates are issued for cases where the aircraft is not certified under the regular categories. These allow operation of certain aircraft for certain purposes.

The experimental certificate is for special cases.


Experimental certificates

Research and development
Showing compliance with regulations
Crew training
Exhibition
Air racing
Market surveys
Operating amateur-built aircraft
Operating primary kit-built aircraft
Operating light-sport aircraft



The light sport certificate is for light aircraft that may be operated under special conditions. There are 5 categories of LSA.


Light sport certificates

Airplanes
Gliders
Powered parachutes
Weight-shift-control aircraft (commonly called trikes)
Lighter-than-air aircraft (balloons and airships)