Accuracy of GPS in Garmin 430/530

Will wrote:


Hold on, and stop changing topics and talking about new issues. There was
never any debate about FAA mandate. The discussion about whether it is
needed or justified is a separate discussion within the thread. Jim made a
comment that the feature I described would double the cost. I was trying
to respond just to that point. I did so by pointing out:

- It won't take more than a man month to simply code the needed algorithms
(and I doubt it would take that).

If you have an avionics engineering background, you should know that
TSO-C129 is not only enabling, it is specific and fairly limiting. The
avionics vendors are constrained by the TSO. The TSO serves a purpose,
to permit an IFR platfrom for GPS terminal and approach operations
within a National Airspace System that has yet to be declared
GPS-primary, much less sole source.

I am very familiar with the Garmin 530. I have also owned three Garmin
aviation handheld units, the 195, 295, and 296. The handhelds have had
progressively sophisticated features that the Garmin 530 does not have
because the 530 had to go through a very extensive certification process
to be qualified for IFR operations. Not so with the handhelds.

Garmin has millions tied up in both their IFR and VFR programs. They
seem to be progressing along quite nicely in providing products
appropriate for the operation.

I have my own ways of independendly verifying the accuracy of my 296 by
using DME at the appropriate time. That provides a great accuracy
check, which is valid for a limited period of time. But, it is hardly
approach RAIM. Also, the TSO-C129 sets actually increase accuracy as
well as assure a high level of integrity in the final approach segment
using approach RAIM.

As I said previously, and you chose to ignore, you seem to be looking
for a full press RNP platform, which would not only have redundant
alerting and actual navigation performance (ANP) it is not limited to
the three levels of sensitivity that TSO C129 constrains; en route,
terminal, and approach. (BTW your handheld does not meet those
sensitivity requirements, either).

A Boeing 727-NG, which is available is a business jet version, has
everything you are looking for, including three IRUs that are constantly
updated by GPS and have position blending. Then, in the event of a
failue of GPS (typically local jamming) the IRUs will continue to
provide very low numbers of RNP accuracy, integrity, and continuity.

I think you might be in over your head a tad and, in the process,
digging a hole for yourself for no good reason. ;-)