Another mid-air (UK)

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.

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

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

Your memory is correct - from the PF 3.4 manual, page 5:
"If available, PowerFLARM uses the barometric altitude from a Mode S transponder installed on the same aircraft. If not, PowerFLARM uses barometric altitude derived from the built-in pressure sensor. Barometric altitude is used for determining the relative altitude to PCAS targets."
My experience is the same as yours - never had a failure to warn on a flarm-equipped glider. I get about 4.5 km average range. I check my installation occasionally using the range analysis tool.

While I'm not in the market for a new glider, I would not buy one without there being provision for a flarm antenna in the tail with an all-around look, and low-loss coax going to the front; with installations being critical, having to shoe-horn them in (I've installed in an SZD-55 (easy), ASW24 (tight for the antennae), ASW20 (same), and Puchacz (still looking for the right space)) shouldn't be necessary.