On Thursday, August 7, 2014 1:15:37 PM UTC-7, jfitch wrote:
On Thursday, August 7, 2014 8:49:07 AM UTC-7, Stats Watcher wrote:

At 15:04 07 August 2014, jfitch wrote:







Isn't the Flarm GPS WAAS corrected? The WAAS standard of



performance is



1.6M nominal horizontal (95%). When the NDGPS system is



functional (and GPS



engines take advantage of it) this will be reduced to 15 cm.











Not in Europe as WAAS is US only. A search of the Powerflarm



website returned 0 (zero) occurrences of the term 'WAAS'. So it



seems unlikley.... Same result for NDGPS, so that seems unlikely



too.. If someone finds something different I will obviously be wrong



but until that point it's still +-16m (ie a whole wingspan) at 99%



confidence



From the Flarm.com product page:



"FLARM incorporates a high-precision WAAS 16-channel GPS receiver and an integrated low-power radio transceiver. Static obstacles are included in FLARM's database."



Nevertheless, WAAS is intended to correct for atmospheric and geometric anomalies, to improve absolute position accuracy. For gliders in close proximity, these errors are tracking. The fact is, the Flarm GPS has several times the accuracy required to perform the expected function.

I'll add to it that IIRC altitude separation is based on pressure altitude, not GPS altitude. But this is all academic discussion. Those who experienced flying with Flarm near other pilots can attest to its accuracy. Not once I got close enough to a collision course with another flarm equipped glider without Flarm alerting me.

Ramy