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What is Ultralight aviation and explain in detail?
Ultralight aviation (called microlight aviation in some countries) is the flying of lightweight, 1- or 2-seat fixed-wing aircraft. Some countries differentiate between weight-shift control and conventional three-axis control aircraft with ailerons, elevator and rudder, calling the former "microlight" and the latter "ultralight".
During the late 1970s and early 1980s, mostly stimulated by the hang gliding movement, many people sought affordable powered flight. As a result, many aviation authorities set up definitions of lightweight, slow-flying aeroplanes that could be subject to minimum regulations. The resulting aeroplanes are commonly called "ultralight aircraft" or "microlights", although the weight and speed limits differ from country to country. In Europe, the sporting (FAI) definition limits the maximum stalling speed to 65 km/h (40 mph) and the maximum take-off weight to 450 kg (992 lb), or 472.5 kg (1,042 lb) if a ballistic parachute is installed. The definition means that the aircraft has a slow landing speed and short landing roll in the event of an engine failure.In most affluent countries, microlights or ultralight aircraft now account for a significant percentage of the global civilian-owned aircraft. For instance in Canada in February 2018, the ultralight aircraft fleet made up to 20.4% of the total civilian aircraft registered. In other countries that do not register ultralight aircraft, like the United States, it is unknown what proportion of the total fleet they make up. In countries where there is no specific extra regulation, ultralights are considered regular aircraft and subject to certification requirements for both aircraft and pilot.

Definitions
Australia
In Australia, ultralight aircraft and their pilots can either be registered with the Hang Gliding Federation of Australia (HGFA) or Recreational Aviation Australia (RA Aus). In all cases, except for privately built single seat ultralight aeroplanes, microlight aircraft or trikes are regulated by the Civil Aviation Regulations.

Canada
United Kingdom
Pilots of a powered, fixed wing aircraft or paramotors do not need a licence, provided its weight with a full fuel tank is not more than 75 kg (165 lb), but they must obey the rules of the air.For heavier microlights the current UK regulations are similar to the European ones, but helicopters and gyroplanes are not included.Other than the very earliest aircraft, all two-seat UK microlights (and until 2007 all single-seaters) have been required to meet an airworthiness standard; BCAR Section S.
In 2007, Single Seat DeRegulated (SSDR), a sub-category of single seat aircraft was introduced, allowing owners more freedom for modification and experiments. By 2017 the airworthiness of all single seat microlights became solely the responsibility of the user, but pilots must hold a microlight licence; currently NPPL(M) (National Private Pilots Licence).

New Zealand
Ultralights in New Zealand are subject to NZCAA General Aviation regulations with microlight specific variations as described in Part 103 and AC103-1.

United States
The United States FAAs definition of an ultralight is significantly different from that in most other countries and can lead to some confusion when discussing the topic. The governing regulation in the United States is FAR 103 Ultralight Vehicles. In 2004, the FAA introduced the "Light-sport aircraft" category, which resembles some other countries microlight categories