On Friday, November 27, 2015 at 2:07:01 PM UTC-8, XC wrote:
Once again I'll say - That is not the way it works. The 2 km does not apply to an aircraft determined to be a threat. In the case stated above the alarm and display would go off at x secs regardless of the distance. I am not sure what the number of seconds is but it is based on a safe reaction time. The warning would be limited by the reception range of the FLARM set up and any limitations the pilot has set in $PFLAU portion of the configuration file. This would be true stealth or not. The specifics of how the threat is painted and the audio warning is left to manufacturer of the display device.

Proximate aircraft which are not a threat are only displayed if they are within 2 km and +/- 300 m, etc.

XC

I don't think that's the issue people are raising. The only way you get a warning from Flarm is if the glider is on an intersecting track within a fairly narrow "uncertainty cone". It is only valid over any distance for gliders that don't maneuver. As we all know that is rarely the case - glider maneuver all the time.

The issue is that a glider that hooks a turnpoint or leaves a thermal or otherwise changes course can go from being invisible to a threat at a distance that is roughly 10-15 seconds away from impact.

The RC is aware of this shortcoming and is engaging with the IGC and Flarm to ensure that course changes cannot generate surprise threats without proper IDs (remember, a radio call to a known Contest ID to coordinate evasive action is the best practice in head-to-head scenarios). It is particularly an issue for high-altitude, high speed street flying that is common in the US west and other places where converging speeds can top 350 MPH. At 2km for Flarm stealth mode this is a 12 seconds of warning. Most pilots who fly under these conditions use longer range situational awareness to avoid conflicts rather than having to react with very little time to: 1) identify and orient the threat, 2) determine the best course of action, 3) raise the other glider on the radio by Contest Number - or worse, Flarm ID (who memorizes theirs?), 4) coordinate an evasive maneuver that isn't "you zig, I zag". Ask the guys that fly the convergence and strong streets out west all the time. Less than a minute to do all that concerns them - deeply. I asked them and got their feedback.

Also, I don't think if you ask the guys in the middle of the scoresheet they'd be super wild about deliberately creating more landouts (and everything that goes with that in terms of hassle and the odd insurance claim) out of some sense that missing a thermal on a random glide that someone who flew 1/16 of a mile to the east stumbled into for a save somehow is more valid. Mostly we devalue contests with landouts because we think landouts are an indicator of less valid conditions. In fact we polled people and they said what they think.

But that's another discussion about philosophy. :-)

9B