Re: anyone running GPS clocks in Southeastern Georgia?

[Owen DeLong <owen () delong com>]

On Jan 21, 2011, at 10:27 AM, Gary E. Miller wrote:

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> Yo All!
>
> On Fri, 21 Jan 2011, Matthew Kaufman wrote:
>
> > I'm not sure how you'd get increasing radius with altitude from anything but a
> > jammer near sea level.
>
> Agreed.
>
> One of these tests was recently run in Utah and we saw the effects
> in Central Oregon well outside the NOTAMed area.  During the tests,
> airplanes using GPS navigation would suddenly lose RAIM and had to
> abort their approach to landing.  Not sure if they lost all GPS nav
> information or just RAIM.
>
> For non pilots, RAIM is an indicator that the GPS has a redundant
> solution that matches the barometrically measured altitude.  GPS will
> continue to report a nav solution when lacking this redundancy but
> pilots are not allowed to shoot an approach when RAIM is off.
>
> Good thing most air carriers do not use GPS yet.
Not true.

Most air carriers do use GPS. Most airliners are even WAAS capable
these days.

Good news is that while RAIM appears to fail under these tests, the
WAAS capable GPSs seem to not lose their ability to shoot LPV
approaches.

Not sure why that is, but, I've been on an LPV approach during one of
these tests when other pilots were calling missed on the LNAV version
of the approach due to RAIM loss and I was able to continue the approach
down to minimums and land.

Owen
(Commercial Pilot, Airplane, Single Engine Land, Instrument Airplane)