Electronic Conspicuity Glossary

ADS-L, ADS-B, FANET, FLARM, Mode S, OGN... this glossary brings together the definitions of the main electronic conspicuity terms for pilots, with links to our dedicated pages to go further on each topic.

ADS-L (Automatic Dependent Surveillance – Light)

ADS-L (Automatic Dependent Surveillance – Light) is an electronic conspicuity standard designed for low-cost, low-power devices. It allows an equipped aircraft to broadcast its position (ADS-L Out) and, depending on the device, to receive the position of other equipped aircraft (ADS-L In). It is not simply a miniature variant of ADS-B: the two standards differ in their technology, their device ecosystem and their regulatory framework. In Switzerland, ADS-L Out is one of the compliance means considered in the plan FASST-CH led by the FOCA. See our dedicated page on l'ADS-L en Suisse.

ADS-L In

ADS-L In refers to a device's ability to receive the position of other aircraft broadcasting in ADS-L Out, in order to display them on an instrument or an application. A device may offer ADS-L Out without necessarily offering ADS-L In, or vice versa: both capabilities depend on the model and must be checked on each device's technical sheet. See our page ADS-L en Suisse for details on use cases.

ADS-L Out

ADS-L Out refers to a device's ability to broadcast its own position and identification according to the ADS-L standard, in order to be perceived by other aircraft equipped with a compatible receiver (ADS-L In). In Switzerland, ADS-L Out is among the compliance means considered by the plan FASST-CH, alongside Mode S and ADS-B Out — the final terms remain to be confirmed by the FOCA. See our page ADS-L en Suisse.

ADS-B (Automatic Dependent Surveillance – Broadcast)

ADS-B (Automatic Dependent Surveillance – Broadcast) is the surveillance and conspicuity standard used by commercial aviation and a large part of general aviation. It breaks down into two distinct functions: ADS-B Out (transmission) and ADS-B In (reception), which a device may offer separately or together. ADS-B is not equivalent to ADS-L: these are two distinct standards, with different equipment and regulatory frameworks. See our page ADS-B.

ADS-B In

ADS-B In refers to a device's ability to receive positions and flight data broadcast by other aircraft in ADS-B Out, in order to display them on board. An ADS-B In receiver alone does not make its carrier visible to others: this visibility depends on ADS-B Out, a separate function that the device may or may not offer. See our page ADS-B.

ADS-B Out

ADS-B Out refers to a device's ability to broadcast its identity, position and flight data, allowing other aircraft equipped with an ADS-B In receiver to perceive it. This is one of the compliance means mentioned for powered aviation within the Swiss regulatory framework being prepared. See our page ADS-B.

FANET

FANET is an ad hoc network developed specifically for free flight (paragliding, hang gliding): equipped devices directly exchange their position, identification and short messages, without going through a telecom operator. It is neither a certified collision avoidance system nor an automatic means of being seen by powered aviation — for that, an additional compatible protocol (ADS-L, FLARM or ADS-B) is still required. See our page FANET et FANET+.

FANET+

FANET+ combines the base FANET network with compatibility with the FLARM ecosystem, the extent of which depends on each manufacturer's implementation — it is not simply a marketing rebrand of FANET. In Switzerland, the current recommendation communicated for free flight generally combines FANET+ and ADS-L Out, with neither replacing the other. See our page FANET et FANET+.

FLARM

FLARM (Flight Alarm) is an electronic conspicuity and proximity alert system historically very widespread among glider pilots. A FLARM device broadcasts its position and receives that of other FLARM devices; on certain compatible models, trajectory computation and a collision risk alert are also added. Not all capabilities are guaranteed across all FLARM-compatible devices — see the definition of PowerFLARM below. See our page FLARM.

PowerFLARM

Trajectory calculation and collision risk alerting are at the core of FLARM itself, not exclusive to PowerFLARM. PowerFLARM is a specific range of devices implementing FLARM, which additionally adds, depending on the model, ADS-B (1090 MHz) and Mode C/S traffic reception, as well as other functions and interfaces depending on the manufacturer. These additional capabilities are specific to the PowerFLARM range and should not be generalized to all FLARM devices on the market: always check the manufacturer's data sheet for a given model. See our page FLARM.

Mode S

Mode S is a surveillance transponder used notably in powered aviation: it responds to interrogations from a ground secondary radar or a TCAS/ACAS collision avoidance system, and can transmit certain information depending on its installation. It is not a synonym for ADS-B — the accuracy and availability of the data received depend on the type of signal emitted and the ground or airborne equipment that receives it. See our comparatif des technologies to place Mode S in relation to ADS-L, ADS-B and FLARM.

Electronic Conspicuity / Perceptibilité électronique

Electronic conspicuity (electronic conspicuity, in English) refers to all the means enabling an aircraft to be electronically detected by other aircraft or by air traffic services, in addition to — never as a replacement for — visual vigilance and the "see and avoid" principle. ADS-L, ADS-B, FLARM and FANET are examples of this, each with its own ecosystem of devices and its own limitations. See our page Perceptibilité électronique.

FASST-CH

FASST-CH is the electronic conspicuity plan led by the FOCA (Federal Office of Civil Aviation) for Swiss airspace. It considers several possible means of compliance, including Mode S, ADS-B Out and ADS-L Out, with an announced deadline that is subject to the outcome of the regulatory process and stakeholder consultation. The exact date of entry into force and the final terms remain to be confirmed by the FOCA. See our page ADS-L en Suisse for the updated status of this matter.

SRD860

SRD860 refers to a short-range radio frequency band (around 860-870 MHz) used by certain European electronic conspicuity systems. Its precise use — which standards use it and in what way — varies according to the standards in force and the implementation of each device; it should not be inferred that it is used identically by all the systems mentioned in this glossary.

GNSS (Global Navigation Satellite System)

GNSS (Global Navigation Satellite System, of which GPS is the best-known example) is the satellite positioning system that provides the position used by ADS-L, ADS-B, FLARM or FANET. GNSS is not itself an electronic conspicuity system: it provides the upstream position data, which these protocols then handle transmitting or receiving between aircraft.

OGN (Open Glider Network)

OGN (Open Glider Network) is a community network of ground receiving stations that pick up and republish certain signals (notably FLARM) emitted by nearby aircraft. OGN is a data reception and sharing infrastructure, not an air-to-air communication protocol: it should not be confused with a standard such as ADS-L or FLARM itself, some of whose information it may retransmit depending on the coverage of the available stations.

Remote ID

Remote ID is a remote identification device for certain aircraft, mainly drones, allowing third parties or authorities to know the identity and position of an aircraft in flight. It is a regulatory concept related to but distinct from the electronic conspicuity of manned aviation (ADS-L, ADS-B, FLARM, FANET): the frameworks, technologies and objectives are not the same.