On Saturday, November 28, 2015 at 1:35:36 AM UTC-8, wrote:
1/4 minute is ample time - that is about when Flarm issues its first acoustic collision alert. I have participated in several head on collision scenarios during a Flarm trial. Even waiting until the third level of Flarm alarm before reacting all that is required is a gentle change of direction a few degrees. The key thing is that Flarm has alerted you to visually acquire the potential threat that you might not otherwise have done.

BTW my strong belief is the the first response to a Flarm acoustic alert should be to look along track, to see a possible head on threat, before looking at the visual display. Head on threats are the most high energy.

There is far too much concentration on Flarm visual displays (eyes down) instead of the acoustic alert (eyes outside).

1/4 minute may be ample in controlled tests between two gliders. It may not be in the real world.

Imagine three gliders at 200 kph slightly separated vertically, horizontally, and longitudenally running a street, meeting 3 gliders similarly displaced on an opposite heading. This is not all that uncommon over the Whites in the west. You have 12 seconds to visually ID the three opposing gliders, account for the two with you, decide on an evasive action and implement it, all without knowing the plans of the 5 other gliders, and making further adjustments when 2 of the other 5 didn't do what you guessed. You cannot visually ID a glider head on against clouds at 2 km, hard even at 1 in a short time. Had you seen them 5 or 10 km away, the situation will not even arise since a minor adjustment would have completely eliminated the possibility.

I have argued against considering Flarm to be that much of a safety device, given that mid air collisions are quite rare. But to have it in the cockpit and then disable it in precisely the conditions most likely to cause a mid air (most of them have been in contests) is odd logic.