GPS Satellite Reception Dropout

[lucaberta]

Originally Posted by Kevin Horton

One day I was doing a proficiency flight with an inspector from Nav Canada. We discovered a repeatable loss of GPS signal NE of CYHM. While discussing this, he mentioned that he had participated in an investigation of another repeatable GPS interference problem that proved to be caused by the television receiver on a boat in a marina. Go figure.

quite possibly he was referring to a case very similar to the infamous Moss Landing (California) Harbor case back in 2001, very well documented here:

http://www.gpsworld.com/gpsworld/art...l.jsp?id=43404

I also found an interesting Powerpoint deck from the 46th Test Squadron of the USAF talking about interference to the GPS signal here:

http://www.navcen.uscg.gov/cgsic/mee...lner%20PRA.ppt

Ciao, Luca

[Aerosport1]

I have a Garmin 430W and a 396 in my Piper. I started having the same problem since I upgraded my 430 to waas. I called the avionics shop and talked to them about it. He said bring it over tomorrow if possible. When I arrived at the shop he walked out and asked what com freq I was on when this happened. I was a little stumped at first but we started trying freqs. that I was on the last time I noticed it. Dialed up 121.00 Cincinatti approach hit my transmit button and got the messages lost satellite. I was shocked. Turned to 121.65 satellite same thing. It turns out that my ELT on 121.5 effects both 430 and 396. We unhooked ELT and the problem went away. We swapped out my elt for another elt from another piper and no problem. Something with my elt. The shop had researched this before I got there and this was from Garmin. My com 1 is my 430 and my #2 radio does it also. The 396 seems to take a little longer to go down. It happens when you transmit on any freq on 121.xx. I ordered a new ELT.

RV-10 QB in progress

[B737NG]

Does anyone ever check the raim predictions for your route of flight?

I just found this handy website: http://raimprediction.net/ac90-100/

For RNP RNAV approaches (airline) the raim predictions are provided for every flight.

Paul

RV-8 Finishing Kit

[Joel]

Ion tails. Check link: http://science.nasa.gov/headlines/y2...nov_africa.htm

[Kevin Horton]

Originally Posted by B737NG

Does anyone ever check the raim predictions for your route of flight?

I just found this handy website: http://raimprediction.net/ac90-100/

I haven't used a program to do the RAIM prediction before flight, but I've done hundreds of RAIM predictions using on board GPS systems. In my experience, there is very poor correlation between the RAIM prediction and whether you will or will not actually have RAIM at the FAF. I've had many cases where the RAIM prediction said there would be a RAIM problem, but we continued with GPS as the weather was VMC, only to find that we did have good RAIM at the FAF. I've had many other cases where the RAIM prediction said everything was OK, yet we did not have RAIM at the FAF.

The RAIM prediction algorithms look at where the satellites will be when you reach the FAF, and see if there will be enough satellites, with good geometry (i.e. the available satellites cannot all be in one area of the sky). The prediction does not use satellites that will be low on the horizon, as it is assumed that your antenna might not be able to pick them up. But, in fact, the GPS antenna usually does receive the satellites that are low on the horizon, so the actual number of satellites available would be higher than predicted, which allows the GPS to have RAIM when it was predicted to not be available.

I believe that many cases of no RAIM at the FAF are due to something interfering with the GPS signals, and this interference cannot be predicted by the RAIM prediction program.

[N941WR]

My soal navigation instruement is a Garmin 496 and I have had issues with it twice, in almost the same location.

Both times were on flights from 3M3 (Collagedale, TN) to 28A (Goose Creek - Charlotte, NC) at 9,500'.

The first instance the GPS just locked up. Turning it off and back on again reset it.

On the second instance I was 60 miles from CLT's Class B airspace and when the GPS updated the image it stopped drawing the Class B upside down wedding cake but remained functional. Once again, turning it off and back on solved this problem.

Have any of you had similar issues with a G496?