A big question is exactly how FLARM has suppressed the tow plane ADS-B alarms. Does FLARM recognize the fact that the tow plane and glider are in formation, and only suppress the alarm while the formation flight continues, or does it somehow completely suppress all alarms for the tow plane? You definitely would want to see tow plane alarms after the glider releases from the tow in the event that you accidentally get on a collision course with the tow plane after the completion of the tow.

Fair question! The suppression works on the geometry of the formation, namely relative headings, relative velocities, relative positions (i.e. vertical and horizontal separation). As soon as the conditions no longer hold, you will get alarms as normal.

This is unchanged to how tow trains are handled in FLARM-FLARM situations. The difference is that for ADS-B targets, the device does not know it is a tow plane - ADS-B simply does not give you this kind of metadata - so the logic is applied to all ADS-B targets. As the geometric conditions are really tight, we believe this is acceptable and will not lead to false negatives..

We are interested to hear how well this works, please do send us feedback!

- Urban, FLARM