On Feb 23, 6:28*am, Ian Strachan wrote:

Many thousands of IGC files have been analysed since then and the
conclusion is still the same, anomalies in GPS altitude in IGC files
continue to occur. *I say "in IGC files" because that is where the
data is from, and more expensive GPS receivers with more sophisticated
processing probably would not show these anomalies.


Ian Strachan
Lasham Gliding Centre, UK
Chairman IGC GNSS Flight Recorder Approval Committee (GFAC)

Ian,

I'd be curious to see the results of the detailed analysis of IGC
files. Is there a place on the IGC site where we could see the data?
I'm not looking for the annecdotal sort (i.e. see this file here) but
the volumetric sort (i.e. based on an automated review of 10,000
files). I had started on this a year back but stopped when I was
told that the IGC was already doing this.

In my experience in writing the specs for running a large batch
analysis program on this topic, what happens is that INDIVIDUAL fixes
or SMALL GROUPS of fixes do display anomalous results. I think most
people recongnize this possibility. However, they can easily be ruled
out by post-flight analysis programs by predefined parameters (for
example, a 10,000 fpm climb rate over a rolling 4 or 6 fix
average).

I think the bigger question that still needs to be answered is "to
what level of precision" do we need all of this to work.
Considering the inherent issues in measuring pressure altitude during
the fluid conditions of a post-frontal day (for example), it feels as
if we are holding GPS to a higher standard.

Thanks in advance,

Erik Mann