SGC's new ATOM GRID system - helping aircraft see your FLARM

By Mark Fisher and John Matthews

At Parham we are all aware that the SGC fleet and most private gliders are now equipped with FLARM.

FLARM was invented in 2004 as a collision risk warning and conspicuity system for gliders. It is able to warn pilots of collision risks in the air, and display other aircraft on the glider's navigation screen. We have to emphasise here that FLARM must always be used as an aid to good lookout, not a replacement.

An extra benefit of FLARM has been the development of some useful web sites and applications which use data received from FLARM equipped gliders. This data is collected by ground receivers like ours and sent to servers maintained by the Open Glider Network (OGN). From there it is available to developers. Details are on the OGN website:

Best known results are the web sites which show glider positions on a moving map in real time, such as "Spot the Gliders" and But applications also include Search and Rescue (SAR), automatic flight logs such as OGN Logbook, and range evaluation tools from FLARM and KTrax.

We have been part of this network since 2015 when our internet connected FLARM receiver went live.

Around 2017 a collaboration took place between OGN and PilotAware (PA), who produce avionics systems for the General Aviation (GA) community. They were investigating how glider FLARM signals could be displayed on PA cockpit systems. The problem was that PA and FLARM transmit on different frequencies and use different protocols, so they came up with an idea they called OGN-R. The R stands for Rebroadcast, because the OGN receivers such as ours at Parham could be modified to rebroadcast the FLARM data on the PA frequency. This was also known as the PilotAware Uplink. Thus PilotAware equipped aircraft within range of the station would see FLARM and OGN-Tracker equipped aircraft on their moving map and collision avoidance systems.

The big advantage is that it could be achieved with no change at all to equipment in either aircraft.

We did not upgrade the Parham receiver at that time because the idea was still evolving and decided to wait until the early problems had been resolved and the way forward was clearer.

In the meantime, PilotAware had been working with a company called 360Radar to further extend the scope of the OGN-R receivers so that in addition to FLARM they could also retransmit PilotAware, Mode-S and ADSB position data of air traffic.

The problem with Mode-S messages is that they do not include position data, so 360Radar developed software to calculate a position by triangulation, using Mode-S data from multiple internet connected receiver stations. This done, the enhanced Mode-S data with position added could be returned to our station and retransmitted to PA users along with the FLARM signals.

In 2020 our club decided on the grounds of safety to install this technology and upgrade our FLARM receiver to a full PilotAware ATOM Station and become part of the ATOM-GRID network.

ATOM (the ground station) stands for Air Traffic Overview and Management

GRID (the network) stands for Ground Relay Infrastructure Domain

A new ATOM station uses 3 antennas, one to receive FLARM, one to receive ADS-B and Mode-S and one to transmit data to PA users.