For reasons of simplicity, all terms referring to unmanned aircraft systems (UAS) will be replaced with the term “drone” below.

 A   B   C   D   E   F   G   H   I   J   K   L   M   N   P   Q   R   S   T   U   V   W   X   Y   Z 


Airspace observer

A person who assists the remote pilot by scanning the airspace in which the drone is operating for potential airborne hazards through unassisted visual scanning. 

Assemblies of people

Assemblies of people have been defined by an objective criterion related to the possibility for an individual to move around in order to limit the consequences of an out-of-control UA.  Qualitative examples of assemblies of people are:

  • sport, cultural, religious or political events;
  • beaches or parks on a sunny day;
  • commercial streets during the opening hours of the shops; and
  • ski resorts/tracks/lanes.


Beyond visual line of sight (BVLOS) operation

A mode of drone operation that is not conducted with visual line of sight (VLOS).



Marking by which the manufacturer indicates that the product conforms to the requirements of the relevant EU harmonisation legislation.

CD  - Characteristic Dimension

The "Maximum UAS characteristic dimension", in short "CD", is a length of a straight line that can be stretched from one point on the UAS geometry to another point. This metric is used to assess thegeneral size of the aircraft and the measurements are made differrently for different types of aircraft.

The characteristic dimension (CD) is usually defined as:

  • the wingspan for fixed-wing aircraft;
  • rotor diameter for rotorcraft;
  • the maximum diagonal dimension for multicopters.

Class marking

The class marking (C0, C1, C2, C3, C4, C5, C6) defines the operational capabilities of your drone and the requirements that pilots must adhere to.

Controlled airspace

An airspace of defined dimensions within which air traffic control service is provided in accordance with the airspace classification. Note: Controlled airspace is a generic term which covers ATS airspace Classes A, B, C, D and E. (Source: ICAO Annex 11)

Controlled ground area

Controlled ground area’ is an area on the ground (on the surface of the Earth) wherethe UAS operator is able to ensure that only the persons involved are present. Sucharea comprises the ‘flight geography area’, the ‘contingency area’ and the ‘ground riskbuffer’. The UAS operator may protect the controlled ground area by means of fencingor using other methods, as appropriate, considering the population density. [source: (EU) 2019/947GM1 Article2(21)]


Drone observer

A person who is next to the remote pilot and who, by direct visual observation of the drone, assists the pilot in maintaining visual contact with the drone and ensuring flight safely.

Dangerous goods

Articles or substances which, in the event of an incident or accident, pose a hazard to health, safety, property or the enviro


Ekin -  Typical Kinetic Energy expected 

  • For fixed-wing aircraft: Typical kinetic energy expected should be calculated using the MTOM and cruise speed.
  • For rotorcraft and multicopters: Typical kinetic energy should be calculated using MTOM and terminal velocity. Terminal velocity calculation guidance can be found on Glenn Research Center | NASA website.

Extended visual line of sight (EVLOS) operation

An Unmanned Aircraft System (UAS) operation whereby the Pilot in Command (PIC) maintains an uninterrupted situational awareness of the airspace in which the UAS operation is being conducted via visual airspace surveillance through one or more human observers, possibly aided by technology means. The PIC has a direct control of the UAS at all time. 



A drone – containing a transmitter and/or a receiver – is essentially a radio unit. Rules of use are governed by the Telecommunications Act, and OFCOM is responsible for managing drone frequencies.
More information can be found in the FAQs.



A function that, based on the data provided by Member States, detects a potential breach of airspace limitations and alerts the remote pilots so that they can take immediate and effective action to prevent that breach.


Limited open category

Transitional category which governs the regulations and requirements for drones without a CE or class marking. Minimally restrictive rules and requirements apply to remote pilots flying their drone in this category.


Maximum take-off mass (MTOM)

The maximum permitted mass of the drone, including payload and fuel (as determined by the manufacturer or builder) with which the drone can be operated.


Populated area

The acceptable quantitative definition of the population density of an area to be considered as populated is: more than 300 ppl/km2 (3 ppl/ha).

Privately built drone

A drone and associated equipment which has been assembled or manufactured by the builder for his own use. Drones and associated systems assembled from components sold by the manufacturer as a prefabricated kit are not covered by this definition. 


Recognized body

A body recognised by the FOCA to carry out practical training and assess the practical skills of remote pilots in the context of a standard scenario. Organisations wishing to be declared a recognised body by the FOCA can find more detailed information in the FAQ.


Sparsely populated area

The acceptable quantitative definition of the population density to be considered assparsely populated is: less or equal to 300 ppl/km2 (3 ppl/ha). 



Official registration, training and examination platform for remote pilots in the ‘open’ category. Operators need to register and undertake training and sit the exam on that platform.

Uncontrolled airspace

No official definition, but in principle it is the airspace which is not controlled. 

Unmanned aircraft system (UAS)

A drone and remote control equipment.

Uninvolved people

Persons who are not involved in the drone operation or who are unaware of the drone operator’s instructions and safety procedures.


Visual line of sight operation (VLOS) 

A mode of drone operation during which the remote pilot is able to maintain uninterrupted visual contact with the drone without the assistance of an observer. 

Last modification 22.06.2023

Top of page