How different is aviation GPS?

You don't need much acuracy to find an airport. They tend to be the
large things with the long areas of pavement. As of today, the use of
GPS as sole naviation for preceision approachs in low visibility (fog)
is limited to "non precision" approaches, just good enough to get you
down to about 500 feet and near the end of the runway. At some point it
should be good enough to actually touch down on the runway with (LAAS).

-Robert


wrote:
As part of my work (civil engineer), I routinely use GPS equipment in
surveying. And construction specifications usually calls for this
equipment to be held stationary for as much as three hours where
crucial transition points are to be located, and for up to twenty
minutes at less important locations.

I guess since you folk use GPS to navigate all across the globe and
requires to be both very precise and instantaneous, my equipment is
very much inferior to what's used in aviation.

Has anyone here used the type of equipment I'm mentioning? You should
see the time the thing I use takes to stabilize itself to show the
elevation... you'd comfortably CFIT if you had that in your airplane
)

Ramapriya

No real difference. The stabilization that you refer to is getting to an
accuracy that is not needed for ground-based or aviation-based navigation.
Typical near-instanstaneous accuracy for even cheap GPS receivers is a few
meters. Not good enough for surveying but certainly good enough to find a
60-foot wide (or better) runway.


-------------------------------
Travis
Lake N3094P
PWK

wrote in message
oups.com...
As part of my work (civil engineer), I routinely use GPS equipment in
surveying. And construction specifications usually calls for this
equipment to be held stationary for as much as three hours where
crucial transition points are to be located, and for up to twenty
minutes at less important locations.

I guess since you folk use GPS to navigate all across the globe and
requires to be both very precise and instantaneous, my equipment is
very much inferior to what's used in aviation.

Has anyone here used the type of equipment I'm mentioning? You should
see the time the thing I use takes to stabilize itself to show the
elevation... you'd comfortably CFIT if you had that in your airplane
)

Ramapriya

I guess since you folk use GPS to navigate all across the globe and
requires to be both very precise and instantaneous, my equipment is
very much inferior to what's used in aviation.


Well, several wrong assumptions here.

1. Most airline aircraft do not or not regularly use GPS to "navigate
across the globe". They use inertial navigation. Some use inertial
navigation with position updates from GPS. GPS is typically used in
general aviation aircraft - because it is cheap.

2. For enroute navigation, GPS accuracy of the standard signal (50
meters or so) is plenty accurate, altitude is measured with
barometrics, not GPS. For approaches to airports, the prevalent method
of navigation is not GPS, but other means (google ILS and VOR). GPS
approaches can make do with standard GPS signals, however, in the US
more and more approaches using WAAS (a method of differential GPS) as
an enhanced signal. However, the approaches down to an automatic
landing are never done with GPS, they use ILS.

2. The key problem in aviation with GPS is immediate feedback to the
airplane in case the signal goes bad, aka signal integrity monitoring.
Certified aviation GPS receivers have higher standards in that regard.

--
Thomas Borchert (EDDH)

In a previous article, said:
I guess since you folk use GPS to navigate all across the globe and
requires to be both very precise and instantaneous, my equipment is
very much inferior to what's used in aviation.

Years and years ago, I was told how to access some diagnostic modes on my
Garmin GPSMAP 195. The diagnostic mode showed the state of all sorts of
internal stuff, and from that it was apparent that one major difference
between the aviation 195 and the marine 175 is that the 195 had
temperature and pressure sensors. I suspect they put that in there so
that they could correct the results from the GPS radio for those factors.
The other major difference was that the 195 had WAY more flash memory to
store all those aviation waypoints.

But the fact of the matter is that aviation or not, GPS doesn't do
altitude as precisely as position because of the basic geometry. There
are numerous explanations of why on-line. So for aviation use, we either
need WAAS (which might or might not be available) or use a barometric
altimeter for altitude, and for surveying you let it sit so it can
accumulate a lot of data and integrate it.

As a former surveyor, I can tell you that the altitude requirements for
surveying are a lot more precise than for aviation - if my bridge abutment
is built 2 feet high, I'm getting fired. If my plane is 2 feet high,
nobody is going to notice.

--
Paul Tomblin http://xcski.com/blogs/pt/
"All life is transitory. A dream. We all come together in the same place at
the end of time. If I don't see you again here, I will see you in a little
while in the place where no shadows fall." - Delenn

Paul Tomblin wrote:
Years and years ago, I was told how to access some diagnostic modes on my
Garmin GPSMAP 195. The diagnostic mode showed the state of all sorts of
internal stuff, and from that it was apparent that one major difference
between the aviation 195 and the marine 175 is that the 195 had
temperature and pressure sensors. I suspect they put that in there so
that they could correct the results from the GPS radio for those factors.
The other major difference was that the 195 had WAY more flash memory to
store all those aviation waypoints.

Paul,
Do you happen to remember what the keystrokes were to get to the 195's
diagnostic mode? I'd be curious to see what mine is saying.

--- Jay


--

Jay Masino "Home is where the critters are"
http://www.JayMasino.com
http://www.OceanCityAirport.com
http://www.oc-Adolfos.com

In a previous article, (Jay Masino) said:
Paul Tomblin wrote:
Years and years ago, I was told how to access some diagnostic modes on my
Garmin GPSMAP 195. The diagnostic mode showed the state of all sorts of
Paul,
Do you happen to remember what the keystrokes were to get to the 195's
diagnostic mode? I'd be curious to see what mine is saying.

Don't remember - it was probably 10 years ago, and probably on this
newsgroup. You might want to see if Google Groups has it. There were two
combinations of three buttons you could hold down as you started it - one
wiped all your routes, tracks and user waypoints, and the other started a
diagnostic mode. Don't get them confused.


--
Paul Tomblin http://xcski.com/blogs/pt/
"All life is transitory. A dream. We all come together in the same place at
the end of time. If I don't see you again here, I will see you in a little
while in the place where no shadows fall." - Delenn

Paul Tomblin wrote:

Years and years ago, I was told how to access some diagnostic modes on my
Garmin GPSMAP 195. The diagnostic mode showed the state of all sorts of
internal stuff, and from that it was apparent that one major difference
between the aviation 195 and the marine 175 is that the 195 had
temperature and pressure sensors.

I've had several handheld, general purpose / outdoor GPS units that gave
temperature and possibly (I don't clearly remember) pressure in
diagnostic mode.

Many newer marine units have external water temperature, depth sensor,
and water speed sensor capabilities, as well as the same memory
capabilites as aviation units. While airplanes need aviation waypoints
and related information, boaters need serious waterway chart storage, so
memory is just as important. The better marine units have the
waterborne equivalent of our VFR charts stored and displayed by the
unit. I really think price differences have more to do with our $70
inner tubes and $50 carriage bolts than technology differences.

Here's one link to diagnostic modes, use at your own risk:
http://www.gpsinformation.org/dale/secret.htm

The rest of the site:
http://www.gpsinformation.org is got enough info to spin your head! G

We've flown with a Garmin 196 next to an eTrex Vista and a 60CS (with an
included magnetic compass and barometric altimeter), the 196 was no more
accurate than the $3-400 handheld units. My co-owner has the marine
clone of the 296, loaded with "BlueCharts", and the unit is just as
accurate, feature laden, and powerful as the aviation model.

In article ,
B A R R Y wrote:

Many newer marine units have external water temperature, depth sensor,
and water speed sensor capabilities, as well as the same memory
capabilites as aviation units. While airplanes need aviation waypoints
and related information, boaters need serious waterway chart storage, so
memory is just as important. The better marine units have the
waterborne equivalent of our VFR charts stored and displayed by the
unit. I really think price differences have more to do with our $70
inner tubes and $50 carriage bolts than technology differences.

Marine units (at least the high-end ones) often have tide charts built into
them too. Unlike winds aloft, tide heights and tidal currents are very
predictable and can be calculated years in advance. A good GPS unit will
have these tables built in, and can superimpose on the displayed chart a
field of current vectors, and tidal water depths.

Marine units also have a feature which is very handy on a boat, but more or
less useless on an airplane (unless you're hauling skydivers). Hit the MOB
(Man Over Board) button, and the unit will immediately store your current
position as a user waypoint and start navigating to it.

They also often have an anchor watch feature, which sounds an alarm if you
ever get more than N feet away from your current position. You do then
after you've anchored to alert you to the possibility that your anchor is
dragging (you set N to however many feet of rode you've put out).

Oh, yeah, and marine units tend to be waterproof. I don't know of many
aviation units that are designed to 1) float, and 2) survive be submersed
in salt water.

Roy Smith wrote:
In article ,
B A R R Y wrote:

.....
Hit the MOB
(Man Over Board) button, and the unit will immediately store your current
position as a user waypoint and start navigating to it.

We use the MOB feature to memorize where we parked the car while
Geocaching. Also, MARK saves a point on a route list. We "drop a mark"
every time a decision (to turn etc) is made. The route can be reversed
to get back to the car.

Paul Tomblin wrote:

As a former surveyor, I can tell you that the altitude requirements for
surveying are a lot more precise than for aviation - if my bridge abutment
is built 2 feet high, I'm getting fired. If my plane is 2 feet high,
nobody is going to notice.


Looks as if I'm missing something central here, as usual

If there is a 4-hour flight that passes over some 10 waypoints and if
the FMGS keeps getting data that's off by 50 meters or so, am I to
understand that the aircraft will still make heading changes, etc.
that'd be in accordance with the programmed flight plan and that none
of the waypoints will be missed or indeed the final destination
precisely arrived at?

And someone mentioned an acceptable accuracy of 0.1 foot in property
surveying. If surveyors in my industry had that much latitude, there'd
be a lot of equipment skids that'd get installed quite inappropriately,
with lots of patched modifications thereon

Ramapriya