Gps signal lost

[Joe Larussa]

Okay this is getting old. Shooting a GPS approach last week into khwd and lost signal right after the final approach fix. Today shooting the GPS approach into KRHV and same thing. Shot the GPS into KLHM and no problem. When on the ground after starting the plane back up after the GPS failure not getting signal again until maybe 5 minutes later. I have had the 530w bench tested, replaced the antenna and new connector on the antenna. Thoughts?

[Mooneymite]

Talk to Garmin.

Garmin knows there is an antenna problem with the 430/530W antennae.

[thinwing]

Is this fairly recent event?Any avionics changes...need more info

[DVA]

Has the coax cable been verified? You can shoot it with a TDR to see if it kinked or crimped along the path and that it exhibits the proper impedance, Your avionics shop will know what I'm talking about.

Also, I think there's a error log associated with 530, if I'm right, I would be saddened in human kind if that wasn't downloaded and checked for faults that could help lead to troubleshooting this.

[Mooney_Allegro]

When I had the 430W/530W units, I had GPS failures that lasted up to 20 minutes while flying IFR.  I called Garmin and was told there was a defect with the antennas, and both were replaced under warranty.  Years later, I replaced the 430W/530W with the GTN750/GTN650 including new antennas.   The same thing happened with new antennas a few times while flying IFR.  Garmin replaced the antennas again and I hadn't had an issue since.  I was told by Garmin that one defective GPS antenna will take out the good antenna, and you'll have both GPS units lose signals.    

When you replaced your antenna, were both antennas replaced if you have two GPS units?  I was also told by Garmin that if the installer tightens the GPS antenna screws down too hard, that will break or weaken something over time and cause the issue.  Garmin told me to make sure the installer uses a torque screw driver, because if the screws are not torqued properly, this will cause the issue.  

[Browncbr1]

28 minutes ago, Mooney_Allegro said:

Garmin told me to make sure the installer uses a torque screw driver, because if the screws are not torqued properly, this will cause the issue.  

Interesting how garmin requires their units to be installed by an authorized garmin dealer, then put the onus on the customer to make sure the installer does it right.  Unbelievable. 

[Piloto]

Check on the last NAV page for satellite signal levels. Typically it will show solid white bars about 3/4 height for a good antenna. If the bars are below half the scale there is an antenna or cable problem. If the bars are not white but clear there maybe an onboard interference problem. Turn off each piece of avionics and check the bars for a solid white indication. Do this test at least 100ft from a building or inflight.

José

[Joe Larussa]

3 hours ago, thinwing said:

Is this fairly recent event?Any avionics changes...need more info

Well oddly enough I had a Garmin G5 installed recently. It is receiving info from the 530.

[Joe Larussa]

1 hour ago, Mooney_Allegro said:

When I had the 430W/530W units, I had GPS failures that lasted up to 20 minutes while flying IFR.  I called Garmin and was told there was a defect with the antennas, and both were replaced under warranty.  Years later, I replaced the 430W/530W with the GTN750/GTN650 including new antennas.   The same thing happened with new antennas a few times while flying IFR.  Garmin replaced the antennas again and I hadn't had an issue since.  I was told by Garmin that one defective GPS antenna will take out the good antenna, and you'll have both GPS units lose signals.    

When you replaced your antenna, were both antennas replaced if you have two GPS units?  I was also told by Garmin that if the installer tightens the GPS antenna screws down too hard, that will break or weaken something over time and cause the issue.  Garmin told me to make sure the installer uses a torque screw driver, because if the screws are not torqued properly, this will cause the issue.  

I only have the one 530w. What's interesting is on both inflight signal loss it was the glide slope to go and the flag popped up on the hsi. I still had the lnav illuminated and didn't get the satellite loss indication till short final. 

[Mooney_Allegro]

Joe,

That's very strange.  Do you ever experience loss of GPS signal enroute or is it always in the approach phase of flight?  When I had my issues while on an IFR flight plan, I would always ask ATC if any other aircraft reported GPS outages, and the controllers always told me nobody else was having issues, so I knew it was my plane.   I know this sounds crazy, but I've read about GPS jammers used by truck drivers to mask where their trucks are.  Is your airport right by a major trucking highway?  Would there be any other transmitting equipment in your plane that could interfere with your GPS?  Since you already replaced your Garmin GPS antenna, I wouldn't know what else to check.  

[M20F]

1 hour ago, Browncbr1 said:

Interesting how garmin requires their units to be installed by an authorized garmin dealer, then put the onus on the customer to make sure the installer does it right.  Unbelievable. 

The FAR's do the same 

[takair]

20 minutes ago, Joe Larussa said:

I only have the one 530w. What's interesting is on both inflight signal loss it was the glide slope to go and the flag popped up on the hsi. I still had the lnav illuminated and didn't get the satellite loss indication till short final. 

You may be losing your encoding altitude or one of the encoder lines.  The vertical portion of WAAS is augmented/monitored using the encoded altitude.  If there is sudden gross error in the encoded altitude,t he integrity monitor would likely flat is as a fault.  Where does your Garmin get its altitude info from?  Does it occur at a particular altitude?  If it is grey code and at the same altitude every time, we can narrow it down to a particular wire.  

[Joe Larussa]

8 minutes ago, takair said:

You may be losing your encoding altitude or one of the encoder lines.  The vertical portion of WAAS is augmented/monitored using the encoded altitude.  If there is sudden gross error in the encoded altitude,t he integrity monitor would likely flat is as a fault.  Where does your Garmin get its altitude info from?  Does it occur at a particular altitude?  If it is grey code and at the same altitude every time, we can narrow it down to a particular wire.  

Not sure where the 530 gets its altitude. I just assumed it came from itself? 

I do have a Garmin gtx330 transponder. Both inflight losses were right after crossing the final approach fix. 

[carusoam]

Joe's list....

1) The WAAS receiver derives its altitude from the gps constellation of sattelites, accurately enough to rely on for vertical guidance...

2) The New G5 attitude indicators are using GPS data to support or enhance their display info...

3) the Garmin radios have had a few different antenna challenges over the last decade. From bad antenna hardware, to old inappropriate antenna wire reused, to antenna placement not matching the installation guide (too close together or to close to something else)

4) MS has some people with interesting skills. Steven has one of the newest and most complete installations of modern Mooney panels.  Pilotó has some deep radio technology skills that show up often.  Knowing how to read signal strength from the onboard computer in the Garmin radio is brilliant.

5) some old radios bleed so much energy they can interrupt GPS signals.  My old Narco nav radio would interfere with my Garmin portable.  I noticed my Garmin come back on line after tuning in the next VOR station... navigating through Florida.  This gives an idea how strong a GPS signal really is...

All stuff I read here... except the Narco bleeder experience is mine... 

Best regards,

-a-

 

[Piloto]

34 minutes ago, Joe Larussa said:

Not sure where the 530 gets its altitude. I just assumed it came from itself? 

I do have a Garmin gtx330 transponder. Both inflight losses were right after crossing the final approach fix. 

 

34 minutes ago, Joe Larussa said:

Not sure where the 530 gets its altitude. I just assumed it came from itself? 

I do have a Garmin gtx330 transponder. Both inflight losses were right after crossing the final approach fix. 

It is possible that a consistent signal loss over an specific area is due to a ground source, like a cell phone tower, a TV station or other. And not all GPS receivers would behave the same when subject to this interference. Check with others at the airport.

It is also possible that interference is coming from the COM/NAV radio when is set to an specific frequency after crossing the final fix, not uncommon.

José

Edited January 30, 2017 by Piloto

[takair]

7 hours ago, Joe Larussa said:

Not sure where the 530 gets its altitude. I just assumed it came from itself? 

I do have a Garmin gtx330 transponder. Both inflight losses were right after crossing the final approach fix. 

It likely gets altitude from the same source as the transponder.  All IFR GPSs need this second source of altitude.  Maybe not the issue if the transponder is reporting correct.  Were you still in radar contact?  Have the shop make sure radio is seated.  The face plate can hang up and cause poor seating.  Strange that it is always same time in flight, but if it is just the VNAV, maybe it's partial seating.  Just to confirm, do you eventually lose the map too and get a message that you have lost GPS coverage?

[Joe Larussa]

8 hours ago, takair said:

It likely gets altitude from the same source as the transponder.  All IFR GPSs need this second source of altitude.  Maybe not the issue if the transponder is reporting correct.  Were you still in radar contact?  Have the shop make sure radio is seated.  The face plate can hang up and cause poor seating.  Strange that it is always same time in flight, but if it is just the VNAV, maybe it's partial seating.  Just to confirm, do you eventually lose the map too and get a message that you have lost GPS coverage?

I was still in radar contact and after I lose the gideslope eventually I lose the rest.

[chrisk]

I had a similar problem with my GTN 650.   The problem was resolved after I removed my Spot Satellite tracker.  --It should not have been causing a problem, but yet it was.  (likely on a burst position update.)   In this case, it was right after the FAF too.   --I'm speculation (and I should know this) that the GPS goes into a higher accuracy mode at this point.

Anyway, it certainly is an interesting experience to be on a final approach, and instantaneously getting no guidance.  I could see this ending very badly in an area with terrain.   I'm just glad the times it happened, I had already broken out, or was training in VFR. 

 

[teg916]

Before you spend too much money, make sure it wasn. Not caused by this. 

 

https://www.faasafety.gov/files/notices/2017/Jan/NTTR_17-01_GPS_Flight_Advisory.pdf

[Joe Larussa]

5 hours ago, teg916 said:

Before you spend too much money, make sure it wasn. Not caused by this. 

 

https://www.faasafety.gov/files/notices/2017/Jan/NTTR_17-01_GPS_Flight_Advisory.pdf

Now that's interesting! I'm into it around 500 bones so far. My avionics guy mentioned today my Elt may be the issue. Said remove the Elt and try the same approach. This only has happened at two airports that are within maybe 40 miles of each other.

[DaveTrish]

Can you please say what the final verdict was that fixed this issue, Joe?  Also, what shop ended up finding and fixing the issue? 

[carusoam]

Welcome aboard Dave...

I’ll let @Joe Larussa know you are asking...

It would help if you described your challenge...

GPS signals are so weak, it is easy to get noise interference...

Also check notams for GPS interference by the powers that control that...

In this aged thread, anything from interference from other radios on board, to aged antenna wires, to ground planes at the antenna, to connections to the transponder, were discussed... all sources of other people’s challenges for the same issue.

Best regards,

-a-

[gacoon]

Do you use the flaps on approach?  If so try it without them.  Flap motor could be going bad and emitting emf or voltage spike.

[bradp]

On 1/29/2017 at 11:18 PM, Piloto said:

 

It is possible that a consistent signal loss over an specific area is due to a ground source, like a cell phone tower, a TV station or other. And not all GPS receivers would behave the same when subject to this interference. Check with others at the airport.

It is also possible that interference is coming from the COM/NAV radio when is set to an specific frequency after crossing the final fix, not uncommon.

José

We just had about a year of GPS signal for unreliable notams.  I’d lose my GMU11 reliability on departure on only one of ourn4 runways.  FAAST, local pilots and NBAA got involved and it eventually got tracked to the wastewater treatment facility from some fancy spectrum analysis the FAA did.  Turns out the pumps and valves for our local $shit treatment are controlled remotely by RF.  That RF equipment was cheap / low quality and bleeding into the GPS spectrum. FAA made the local utility turn off and replace their RF transmitters and now all is well. 

[RobertGary1]

Maybe someone on the ground was using a 5G phone.