This thread shows the strengths and weaknesses of FLARM.
FLARM was invented in 2004 as a means of close-in collision avoidance (not traffic awareness) for gliders, which often fly in close proximity to each other, especially during gliding competitions, but which fly at relatively low airspeeds (45-90 kts).
FLARM has a very large number of users within the gliding community in the UK and in mainland Europe. It provides very effective collision avoidance for gliders, giving a clear visual and aural alert of potential collision with a low false alarm rate, and without needing to spend time heads-down looking at a traffic display. FLARM is also very low power, which is an important consideration for gliders, which rely on batteries to provide electrical power. Naviter has recently introduced the Oudie 5 with integrated FLARM, so we can expect increasing numbers of paragliders to transmit FLARM.
FLARM has since been extended to become a traffic awareness system, first by the introduction of FLARM Radar in software such as SeeYou Mobile and dedicated traffic displays such as FlarmView, later with the introduction of the Open Glider Network (OGN) and websites such as https://live.glidernet.org
, and most recently by the support for OGN rebroadcast (OGN-R) in PilotAware.
OGN-R is a very worthwhile development. It greatly increases the effective range of FLARM but (and it is a big but), both the FLARM-equipped aircraft and the PilotAware-equipped aircraft need to be in line of sight of an OGN-R ground station. This is not a problem in the flatlands of southern England, but is more of a problem in Wales and Scotland, where there are fewer OGN-R ground stations but also mountainous terrain, so that low-flying aircraft can be out of line of sight even when relatively close to a ground station.