There is prolly a simple answer to this but I haven't seen this before so I thought I would throw this out to the group. My partner has our users guide and he can't find it at the moment.

Friday I flew from Moab to Cal Black Airport, about an hours' flight, and I noticed when I landed the GPS had me out in the weeds, 0.4 miles from the airport. There was a little blue ring around the airplane on the screen and the airport was depicted to my right, 0.4 miles away. Strange, I thought. Perhaps the coordinates of the airport are off in the database?

We shut down and re-started about 20 min. later and the same picture was depicted on the screen. So we flew to HVE and the same thing happened, only it said 0.5 miles from the airport. We then flew to Moab and it tracked us strait to the airport but it now said we were 0.7 miles from the airport after we shut down in front of the terminal.

Is this thing tracking to VOR's instead of airports?? I don't think I had done anthing different than I had for the last 2 years but something has changed!! I don't get the " You are arriving at KCNY" at the bottom of the screen either.

Help.

Many possible errors to us that cannot recieve the encrypted signal. If you can stand it, read this article. http://en.wikipedia.org/wiki/Global_Positioning_System
I don't think there was anything wrong with your reciever. But now having seen it, you understand why I'm leery of TAWS for example in these recievers without RAIM.

Did you take note of how many satellites you were receiving? Was WAAS enabled?

The ring usually indicates a reduced resolution, due to fewer satellites received, or Wide Area Augmentation disabled.

The GPS page in the Main Menu will tell you the number of received satellites and position accuracy. What was yours reporting?

1SeventyZ wrote:Did you take note of how many satellites you were receiving? Was WAAS enabled?

The ring usually indicates a reduced resolution, due to fewer satellites received, or Wide Area Augmentation disabled.

The GPS page in the Main Menu will tell you the number of received satellites and position accuracy. What was yours reporting?

I'm not sure on the # of satellites, should have checked. I know that everything worked well on Thursday's flight but Friday was all out of sorts. I believe that WAAS cannot be disabled unless you go into the menu-GPS page and disable it. Perhaps there was a shortage of receiving/transmitting satellites but its the first time its happened to me.

From your description I can't tell whether you are selecting go direct or a programmed course selection? I would switch from a program to nrst / go direct to see if the receiver is reacting to your program or less satellite coverage as suggested. Then go back to a selected programmed course. Also play with the menu button window to see what is highlighted while in flight.

I've seen the blue ring, but I think it was on my ground GPS. I don't think I've seen it on my 265, 296 or 396. I think I see the blue ring on the car GPS when it overzoomed. I looked at Garmins web site on their downloadable manuals. I couldn't find any mention of a blue ring.
Anybody find a blue ring in an aviation manual?

SixTwoLeemer wrote:Perhaps the coordinates of the airport are off in the database?

The coordinates for an airport in a GPS data base are for the "Airport Reference Point" http://www.ngs.noaa.gov/AERO/arpcomp/arpframe.html, which is defined as " the approximate geometric center of all usable runways. The ARP position computation is somewhat similar to a center of mass computation, except that only two dimensions are considered."

Are you sure that the "dist to airport" number didn't go to zero as you passed the middle point on CNY's single runway?

Next time you fly, switch to the data page which shows the Signal to Noise SNR for each of the satellites you are receiving at the moment. Play with antenna placement to see if there is an effect on SNRs. Also, if the puck is too far aft on the dashboard, the wing blocks the signals, and the SNRs change based on heading.

Finally, while watching the SNRs, try turning off first one NAV/COM and then the other. My Narco NAV receiver, if tuned to 115.5MHz (PUC vor) totally wipes out my GPS (14th harmonic of the receiver Local Oscillator lands on the GPS frequency).

a64pilot wrote:I've seen the blue ring, but I think it was on my ground GPS. I don't think I've seen it on my 265, 296 or 396. I think I see the blue ring on the car GPS when it overzoomed. I looked at Garmins web site on their downloadable manuals. I couldn't find any mention of a blue ring.
Anybody find a blue ring in an aviation manual?

I think Jody is correct and jogged my memory. Iv'e seen the blue ring but I kept trying all the settings on my 396 but never on the 296 and it turned out to be a zoom issue if memory serves.
The way to verify is to go nrst / direct to an airport if this works it is most likely the zoom.

I've been using my 396 for just shy of three years now. It has been flawless, EXCEPT...

In the boonies it always works, comes to life in seconds, and has never let me down. Near cities is a whole different story. From about ten miles south of Troutdale in to the airport my satellite reception just goes away. Nothing. It's completely blind. Five miles north of Eugene and into the airport, same thing. Down in the Phoenix area I can tell you the exact spot on the ground between Goodyear and Stellar Airpark where the damn thing is gonna quit.

Drives me friggin' nuts. I don't get lost out in the middle of nowhere. It's big city airspace that I want, and pay for, that moving map to be working to keep me exactly where I belong.

I've turned Nav/Comms off and on. Changed radio frequencies all to no avail. I've updated the Garmin software, and called their useless customer service I don't know how many times, and get told the same thing every time. "We've never heard of that problem before."

What I've learned to do for big city trips, is stuff my antique Garmin 89 up on the glareshield, and let it run on battery power. It NEVER fails to work, and when the 396 turns into a high dollar XM radio receiver, the 89 will get me where I need to go.

Gump

a64pilot wrote: I think I see the blue ring on the car GPS when it overzoomed.

That's because the ring represents the area of possible error in location. When overzoomed, it's necessary to show the ring to indicate that location can't be known with such high resolution.

GumpAir wrote:...my satellite reception just goes away. Nothing. It's completely blind.

Weird. All a GPS receiver does is receive radio signals from satellites and compute location, so perhaps those frequencies are being jammed/interfered with/stepped on by something on the ground? Yet the 89 prevails...

GumpAir wrote:....From about ten miles south of Troutdale in to the airport my satellite reception just goes away. Nothing. It's completely blind. Five miles north of Eugene and into the airport, same thing. Down in the Phoenix area I can tell you the exact spot on the ground between Goodyear and Stellar Airpark where the damn thing is gonna quit...

Disconnect the coax cable from the ELT antenna where it goes into the ELT and try your GPS again. If that fixes it, it is because high signal levels from very high power TV and FM transmitters couple into the ELT antenna, travel down the coax, mix and generate intermodulation products in the ELT's transistor output stage (even though it is unpowered), the intermod products travel back up the ELT coax, and then radiate off the ELT antenna to the GPS antenna, where they clobber the very low level GPS signal.

If you tell me that you are using one of the ELTs that have an antenna inside the cockpit, same deal; just leave it home for a test flight.

What kind of ELT do you have?

I recommend that you check the Garmin download site and make sure you have the latest software version. My 396 had numerous upgrades including
satellite reception and display clarity. It is easy and free assuming you have the connection cable

MikeMl wrote:

GumpAir wrote:....From about ten miles south of Troutdale in to the airport my satellite reception just goes away. Nothing. It's completely blind. Five miles north of Eugene and into the airport, same thing. Down in the Phoenix area I can tell you the exact spot on the ground between Goodyear and Stellar Airpark where the damn thing is gonna quit...

Disconnect the coax cable from the ELT antenna where it goes into the ELT and try your GPS again. If that fixes it, it is because high signal levels from very high power TV and FM transmitters couple into the ELT antenna, travel down the coax, mix and generate intermodulation products in the ELT's transistor output stage (even though it is unpowered), the intermod products travel back up the ELT coax, and then radiate off the ELT antenna to the GPS antenna, where they clobber the very low level GPS signal.

If you tell me that you are using one of the ELTs that have an antenna inside the cockpit, same deal; just leave it home for a test flight.

What kind of ELT do you have?

Mile,
What the He** do you do for a living?

a64pilot wrote: What the He** do you do for a living?

Retired PhD EE and Extra Class Ham.

Call Garmin and they will talk you through resetting the satellite algorithm(?).
Happened to me once (296) and it only took a few minutes to resolve.
It has to be done on the ground while stationary.
When it happened to me, it was after downloading software updates.
I'll look for some more info on this and post it if I find it.

Fraser
'80 A185F

OK, follow up from my previous post........

The problem my unit had was it lost track of the date. It was five days off.
My unit was way off, perhaps yours was only a day or hours off.

Garmins procedure was to, with the unit off, hold down the "Out" button while turning the unit on. Continue holding the "Out" button for at least 12 seconds. The unit will go into its reset mode and they say it could take up to 30 minutes to reset. Mine took about 10 minutes and I lost no data. Obviously you should have good reception when performing this reset.
This was early September and it's worked fine ever since.

Good luck.

Fraser
'80 A185F

I think you mean the satellite almanac. The almanac is the database that tells the GPS that at this date and time what the satellite geometry will be. The old GPS's that used to take 10 min or so to "find themselves" would not save the almanac and had to download it every time. If your GPS loses the date and or time then the satellite positions will not make sense and it cannot "find itself". This can be observed by watching the reception page and seeing the list of satellites changing and satellites being received and then dropped.
Usually most GPS's will allow an initial position and date / time to be inputted to allow it to find itself quicker. On my 295,296 and 396 there is a selection of "stored without batteries" that causes it to download the almanac and start over, or at least I assume that is what it does. My 396 will sometimes for no reason on initial start up not be able to find itself and a menu that highlights simulator mode will pop up, if I highlight and enter stored without batteries, it will find itself, if I select keep acquiring, it never will.
I've gotten to where I fly with two of these things now since my 396 locked up south of Cuba over water on the way to Costa Rica once. I don't care who you are, your not navigating over water on a map

Almanac.
I knew it was something like that.....I stand corrected. What corner would you like me to stand in?
I have a Garmin GNC 250XL panel mount as a backup. I just don't like the display...or the cost of the database....or the lack of color.....or.......
But it's come in handy more than once.

Fraser
'80 A185F

Mark, I wasn't trying to be an ass, sorry if I sounded like I was, just if someone wanted to look up the problem or something it's easier if you know what it's called. Here is one definition, pretty simple, I'm sure there are better definitions http://gps.about.com/od/glossary/g/GPS_Almanac.htm

A64,
I have thick skin...
That's why I put a question mark after algorithm.
One things for sure, I'm not an expert on anything.

Fraser