Ultralight aircraft in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 are much smaller and lighter than ultralight aircraft in all other countries.

In the USA ultralights are classified as vehicle

Vehicle

A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....

s and not aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 and are thus not required to be registered or for the pilot to have a pilot licence or certificate.

US definition of "ultralight"

Regulation of ultralight aircraft in the United States is covered by the Code of Federal Regulations

Code of Federal Regulations

The Code of Federal Regulations is the codification of the general and permanent rules and regulations published in the Federal Register by the executive departments and agencies of the Federal Government of the United States.The CFR is published by the Office of the Federal Register, an agency...

 Title 14 (Federal Aviation Regulations

Federal Aviation Regulations

The Federal Aviation Regulations, or FARs, are rules prescribed by the Federal Aviation Administration governing all aviation activities in the United States. The FARs are part of Title 14 of the Code of Federal Regulations...

) Part 103 or 14 CFR Part 103, which defines an "ultralight" as a vehicle that:

• has only one seat
• Is used only for recreational or sport flying
• Does not have a U.S. or foreign airworthiness certificate
• If unpowered, weighs less than 155 pounds
  Pound (mass)
  The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
  
  
• If powered:
  1. Weighs less than 254 pounds (115 kg) empty weight, excluding floats and safety devices
  2. Has a maximum fuel capacity of 5 U.S. gallons (19 L);
  3. Has a top speed of 55 knots (102 km/h; 63 mph) calibrated airspeed at full power in level flight
  4. Has a power-off stall
     Stall (flight)
     In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
     
     speed of 24 knots (45 km/h; 28 mph) calibrated airspeed or less

Certification

• Ultralight vehicles and their component parts and equipment are not required to meet the airworthiness certification standards specified for aircraft or to have certificates of airworthiness.
• Operators of ultralight vehicles are not required to meet any aeronautical knowledge, age, or experience requirements or to have airman or medical certificates.
• Ultralight vehicles are not required to be registered or to have registration markings.

Operations

• Ultralight vehicle cannot be flown except between the hours of sunrise and sunset.
• Ultralight vehicles may be operated during the twilight periods 30 minutes before official sunrise and 30 minutes after official sunset or, in Alaska, during the period of civil twilight as defined in the Air Almanac, if:
  1. The vehicle has an operating anti-collision light visible for at least 3 statute miles
  2. The flight is only in uncontrolled airspace

Ultralight vehicles cannot be flown over any congested area of a city, town, or settlement, or over any open air assembly of persons.

Weight allowances can be made for amphibious landing gear, and ballistic parachute systems.

In the United States, while no license or training is required by law for ultralights, training is highly advisable.