Accuracy of GPS in Garmin 430/530

Will wrote:
Is there any way to have the Garmin 430/530 put its current display accuracy
on the primary display as an ongoing statistic, based on the number of
satellites in view? How, in general, do the Garmin units notify you of
situations where GPS accuracy has been compromised to a level that makes it
unsafe to use the Garmin for a GPS approach?

Why would you want that information? In single-pilot operations,
especially, looking at those data constitutes information overload.
That is what RAIM is all about, to keep it simple. RAIM is much more
robust for the final approach segment than for terminal mode. You
simply aren't going to have issues with an IFR-certified GPS (properly
installed) that you will have with a hand-held.

I got an interesting lesson in GPS recently while traveling with a handheld
GPS as the passenger in a plane. The GPS showed us landing about two miles
east of the airport. I figured out only later that the position of the
antenna was such that many satellites were blocked, so the accuracy of the
GPS signal was greatly diminished.

That large of an error was probably due to the substantial altitude
change of the airliner while your GPS was staggering along in 2-D mode.

The particular software I was using
didn't display its current accuracy on the primary display. Based on that
event, I realize I cannot just trust a GPS display without first
understanding the current accuracy of the signal.

As others have told you, the portable does not have RAIM. It is a VFR
device. It was not designed to be robust through a cabin window of an
airliner. Some owners, who are savvy on this still, install an external
antenna on their aircraft for their hand-held GPS. It will never have
the problems you experienced with an external antenna.

What would be really nice is if the primary display would show vertical and
horizontal accuracy as two separate numbers, based on some high confidence
interval (99.99+%). Knowing that the current display reading is accurate
to 10 ft vertical and 15 ft horizontal, for example, might make you a lot
more comfortable in following a GPS approach than a display where the 99.99%
confidence interval is 2000 ft vertical/horizontal (i.e., GPS reliability is
completely compromised by virtue of blocked satellites, bad GPS antenna,
etc).


Again, RAIM and proper IFR installation procedures mitigate your
concerns to the point of being irrelevant.

There is different, higher level of accuracy, integrity, and continuity
than "plain vanilla" TSO-C129 IFR GPS. That is an IFR-approved RNP
platform, which is a quandum leap in RNAV integrity. RNP platforms have
enough information to make you happy in your quest. But, the displays
and software are presently heavy iron stuff, and huge overkill for most
IFR operations today.

"Sam Spade" wrote in message
news:l8n3g.174223$bm6.98713@fed1read04...
I got an interesting lesson in GPS recently while traveling with a
handheld
GPS as the passenger in a plane. The GPS showed us landing about two
miles
east of the airport. I figured out only later that the position of the
antenna was such that many satellites were blocked, so the accuracy of
the
GPS signal was greatly diminished.

That large of an error was probably due to the substantial altitude
change of the airliner while your GPS was staggering along in 2-D mode.

I think the reason may have been that most satellites were blocked inside
the cockpit. But why would anyone object to this non-FAA software simply
self-reporting that its current accuracy was some huge number of horizontal
and vertical feet (i.e., that it was not currently very accurate)? I
cannot understand why anyone would feel that this is a bad thing to tell a
user of that device. If you don't want the information then ignore it.


airliner. Some owners, who are savvy on this still, install an external
antenna on their aircraft for their hand-held GPS. It will never have
the problems you experienced with an external antenna.

That's a great idea. Maybe more handheld GPS users would become aware of
the need for for an external antenna if their GPS software clearly
communicated when the signals they are getting are not very accurate? That
fact might inspire more users of these devices to understand that antenna
placement is quite critical for these devices.

--
Will

But why would anyone object to this non-FAA software simply
self-reporting that its current accuracy was some huge number of horizontal
and vertical feet (i.e., that it was not currently very accurate)?

Because it's a source of more bugs.

Jose
--
The price of freedom is... well... freedom.
for Email, make the obvious change in the address.

And it could double the cost of the system for no useful
purpose.


I'm sure that if anybody wanted a custom made GPS unit,
Garmin or some other company would be happy to take your
million dollars and build you one or even two of them.



--
James H. Macklin
ATP,CFI,A&P

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Jose" wrote in message
. com...
| But why would anyone object to this non-FAA software
simply
| self-reporting that its current accuracy was some huge
number of horizontal
| and vertical feet (i.e., that it was not currently very
accurate)?
|
| Because it's a source of more bugs.
|
| Jose
| --
| The price of freedom is... well... freedom.
| for Email, make the obvious change in the address.

As the lawyers like to say in court "evidence not in the record." There
is no proof at all for the claim that some straightforward math calculations
in any GPS software is going to to double the cost of the GPS. What I was
describing doesn't require any new hardware, and it's just a matter of
calculating some accuracy numbers and representing them in the standard UI.

If it prevents one death that results in a multi-million dollar lawsuit, it
would payback the one man-month of work it might take to do those
calculations in software 100 fold or more.

--
Will


"Jim Macklin" wrote in message
news:4bx3g.8797$ZW3.1447@dukeread04...
And it could double the cost of the system for no useful
purpose.

I'm sure that if anybody wanted a custom made GPS unit,
Garmin or some other company would be happy to take your
million dollars and build you one or even two of them.

--
James H. Macklin
ATP,CFI,A&P

Will wrote:
As the lawyers like to say in court "evidence not in the record." There
is no proof at all for the claim that some straightforward math calculations
in any GPS software is going to to double the cost of the GPS. What I was
describing doesn't require any new hardware, and it's just a matter of
calculating some accuracy numbers and representing them in the standard UI.

If it prevents one death that results in a multi-million dollar lawsuit, it
would payback the one man-month of work it might take to do those
calculations in software 100 fold or more.


How would the use of the GPS be responsible for someone's death?

For VFR work, handeld or otherwise, GPS is an advisory system only, and
not guaranteed. User beware. Have alternative nav sources, like people
did for decades before GPS came on the scene. Did you read the
dislaimers on your GPS's packaging when you got it? Didn't read em? Too
bad.. Didn't buy it new and have the original packaging? Still your
problem. And being in VFR.. you shouldnt have to worry about conditions
bad enough to require an approach.

For IFR work, either you have a good signal, or you do NOT have a good
signal (as calculated by your reciever, and displayed in the form of a
RAIM integrity warning). No shades of gray here.

Based on the past few days worth of posts.. I'm guessing you haven't
done much in the way of actual IFR approaches to minimums.. and I am
also predicting you've not done any of it behind IFR approved GPS
devices, after having thoroughly read the manual and recieved training
in such... workload and workload reduction is crucial. What you propose
is to add workload, unnecesarily, to give quanititative data (percentage
points/errors) regarding something that is already addressed in a
qualitative manner (RAIM OK or NOT OK).

Now you try to justify its cost/benefit by a hypothetical lawsuit over
the lack of something that is not mandated, not needed and not justified?

Sorry... doesn't add up.
Dave

"Dave S" wrote in message
ink.net...
How would the use of the GPS be responsible for someone's death?

Cessna lost a famous case that steered it out of general aviation for a few
years and got a one billion dollar judgement because a pilot hit a fence.
How was it Cessna's fault that the pilot hit the fence? Heck if I can
figure that out, but if a case can be made a lawyer would go for the money.


Now you try to justify its cost/benefit by a hypothetical lawsuit over
the lack of something that is not mandated, not needed and not justified?

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).

- There wasn't any proof for the claim in any case.

- To the extent it might control some kinds of liability it might actually
be cost beneficial rather than just incurring some additional labor cost.

--
Will

you do it, you built it and get rich.
"Will" wrote in message
...
| As the lawyers like to say in court "evidence not in the
record." There
| is no proof at all for the claim that some straightforward
math calculations
| in any GPS software is going to to double the cost of the
GPS. What I was
| describing doesn't require any new hardware, and it's just
a matter of
| calculating some accuracy numbers and representing them in
the standard UI.
|
| If it prevents one death that results in a multi-million
dollar lawsuit, it
| would payback the one man-month of work it might take to
do those
| calculations in software 100 fold or more.
|
| --
| Will
|
|
| "Jim Macklin" wrote
in message
| news:4bx3g.8797$ZW3.1447@dukeread04...
| And it could double the cost of the system for no useful
| purpose.
|
| I'm sure that if anybody wanted a custom made GPS unit,
| Garmin or some other company would be happy to take your
| million dollars and build you one or even two of them.
|
| --
| James H. Macklin
| ATP,CFI,A&P
|
|

There
is no proof at all for the claim that some straightforward math calculations
in any GPS software is going to to double the cost of the GPS.

Have you ever written software?

If it prevents one death that results in a multi-million dollar lawsuit, it
would payback the one man-month of work it might take to do those
calculations in software 100 fold or more.

It is actually more likely to =cause= a death - to a pilot who decides
to rely on a handheld because it has RAIM.

Jose
--
The price of freedom is... well... freedom.
for Email, make the obvious change in the address.

In article ,
Jose wrote:

It is actually more likely to =cause= a death - to a pilot who decides
to rely on a handheld because it has RAIM.

Jose

And tell me that pilots aren't already using those "for situational
awareness only" extended runway centerlines drawn on the moving maps of
VFR-only handhelds to cobble up their own instrument approaches?