On Wednesday, May 30, 2012 7:09:30 AM UTC-4, Richard Brisbourne wrote:

Couple of points worth mentioning here. First, the
SSA approval for flywithce appears only to accept
GPS altitude for verifying flight continuity- a seperate
pressure device is required for height claims.

Second- not all consumer GPS chipsets are equal.
It's interesting that the BGA have withdrawn approval
for the Oudie as a position recorder because the Atlas
V chipset in the new, bright, version, is optimised for
use in motor vehicles, and has track smoothing built
in. This can give significant position errors whenever
you do something (like a tight turn just before an
observation zone) which you couldn't do in a car.

There's been a bit of correspondence about this in the
LK8000 forum, and the expert view there is there's no
way round this.

When we were looking at COTS recorders a few years back (now GPS Position Recorders), I played around with a couple of different units. I found that the majority of COTS units (Garmins leap to mind) did some sort of "smoothing" or "projecting" when they lost signal briefly. This was tested by driving a known course at known times and blocking the antenna with a metal shield for a few seconds.

The takeaway was not that these GPS Position Recorders were inherently unusable but that some amount of care would need to be taken in post flight analysis. In the case that Tony mentions, post-flight analysis works given the impossible climb and descent rates that were noted.

Note that fully-compliant IGC FRs are subject to additional requirements including recording fix validity, satellites in use, etc. and undergo significant testing for the above sorts of problems. Given that the SSA and other NACs, as well as the IGC GFAC are pretty much all volunteer organizations, it's tough to ask for a lot more formal testing to be done. Unless, of course, some of the folks writing in this thread are interested in volunteering...

Erik Mann (P3)
SSA FAI Badge and Record Committee