What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Loss of GPS satellite signal while approaching in IMC

GalinHdz

Well Known Member
Since there was a tropical system overhead us yesterday and the weather really sucked I went to the hangar to do some minor cleaning. While listening to the tower I heard a Saratoga on the RNAV to Rwy 13 get cleared to land. A short while later the Saratoga told the tower the GPS had lost satellite signal (RAIM) and they had to execute the missed approach. They went around in the clouds and returned to Jacksonville approach.

Right then a Citation came on frequency also on the RNAV Rwy 13 approach and was also cleared to land. Right after being cleared the Citation told the tower the GPS had lost satellite signal and they had to execute the missed approach. The tower told him the aircraft before them had gotten the same indication and had also executed the missed approach. I heard them go around in the clouds and they also returned to Jacksonville approach.

A few minutes later the Saratoga came back on frequency but this time "VFR" below the clouds (clouds were now about 1,000ft) and they landed on RWY 13. Once on the ground the Citation came back on tower frequency but he was executing the ILS approach to RWY 31. They landed on RWY 31 with maybe a 5kt tailwind.

This is the 1st time I had heard this actually happen (GPS unuseable for landing in bad Wx) with one of the airplanes having to use the old fashion ILS to land. Now I am REALLY glad I still have ILS capability in my airplane and don't rely exclusively on the GPS "Magenta line".

This is the Saratoga track on FlightAware.

This is the Citation track on FlightAware.

Moral of the story... unless it is a life and death emergency situation, DON'T DO RNAV APPROACHES WITH A NON CERTIFIED GPS!

:eek:
 
Last edited:
It happened to me in vfr. I was right seat, student under the hood. LPV 25R LVK. At about 2000? student says, ?I don?t think the glide slope is working?. I point to the gtn650, which is now showing ?LNAV?, tell student to use those minimums. At about 1000?, near MDA, a big red x appears over the screen, cdi flags. We landed vfr. Never did hear the reason for the outage.
 
I love my VAL INS-429 !! Even if the ILS goes out in one airport it'll be ok at the next airport right beside it.
 
Last edited:
It happened to me in vfr. I was right seat, student under the hood. LPV 25R LVK. At about 2000? student says, ?I don?t think the glide slope is working?. I point to the gtn650, which is now showing ?LNAV?, tell student to use those minimums. At about 1000?, near MDA, a big red x appears over the screen, cdi flags. We landed vfr. Never did hear the reason for the outage.
Now imagine that happening in hard IMC. I bet the pucker factor went up in those cockpits, at least for a little bit. :cool:
 
Now imagine that happening in hard IMC. I bet the pucker factor went up in those cockpits, at least for a little bit. :cool:

Yep. LVK is, in that sense, a lot worse than flat Florida. It?s surrounded by hills, and down low it?s below radar coverage.
 
This is why I still recommend the 650 to my IFR panel customers.
I have the 650 in my own RV and practice using the ILS frequently, the 650 will auto transition from GPS to the ILS with no button pushing.
 
Walt. To make sure I'm understanding you correctly; If I select an LPV approach and the GPS tanks, the 650 will automatically kick over to an ILS for the same runway?

I've got a ton of time with a G-1000 and don't recall ever discovering this. Have I just not got deep enough in the book or is this specific to the 650/750?
 
I am wondering how do you fly the GPS missed approach without GPS guidance?? Is there a procedure specific to this other than vectors?
I am also keen to know more about the GTN automatically switching to ILS with loss of GPS guidance.
Thanks.
Johan
 
I think you misunderstood Walt. If you tell the box ?ils25?, but put or leave the box in gps mode to navigate to an IAF, the box will auto switch to ?vloc? when you intercept.
Yes, if you lose gps then a gps based missed approach procedure is of doubtful usefulness.
I have maintained a separate SL30 just in case my entire 4xxW box dies. In IMC I keep it tuned to the ILS at my home field, so I can quickly transition. And the ILS has a different MAP than the LPV.
 
He's probably referring to not having to hit the OBS button to switch from GPS to ILS on the CDI.
 
I wonder if any of them ran a RAIM prediction.
I wonder, can you look for historical RAIM data? I only know about looking forward.
There is a famous story where a guy with a GPS jammer in his work truck fouled the LAAS beacon at Newark.
 
He's probably referring to not having to hit the OBS button to switch from GPS to ILS on the CDI.

I believe the CDI button is used to switch from GPS to VLOC. The OBS button is used for OBS mode or un-suspending, such as after the MAP on an approach to start the missed appr sequience.

Larry
 
I believe the CDI button is used to switch from GPS to VLOC. The OBS button is used for OBS mode or un-suspending, such as after the MAP on an approach to start the missed appr sequience.

Larry
Ah, yes, you are correct.
 
I wonder if any of them ran a RAIM prediction.
I wonder, can you look for historical RAIM data? I only know about looking forward.

What is predicted and what actually happens can be two very different things. :cool:
 
Last edited:
What is predicted and what actually happens can be two very different things. :cool:

Correct but it would be interesting to see how well the computers predicted it and on a less important note how well those guys did their preflight planning.
 
Somebody will undoubtedly correct me on this if I'm wrong (again), but my understanding is that WAAS means that RAIM is not required. And based on hazy recollections of technical articles that I only sort of understood, there are lots of ways of doing RAIM, depending on how that individual GPS receiver processes the GPS signals to get a position.

And it might also be the case that although signal quality was not good enough for an approach, there were enough GPS signals to allow basic navigation.

Lotsa details...
 
Correct but it would be interesting to see how well the computers predicted it and on a less important note how well those guys did their preflight planning.
Two independent and completely different aircraft having the same issue at the same time in the same airspace reduces significantly the posibility of crew error. Both airplanes landed safely without a problem so both aircrews executed an effective alternate plan.

Lets not fall in to the "just blame the pilot(s)" syndrome we complain the FAA is too quick to do.

:cool:
 
Last edited:
Two independent and completely different aircraft having the same issue at the same time in the same airspace reduces significantly the posibility of crew error. Both airplanes landed safely without a problem so both aircrews executed an effective alternate plan.

Lets not fall in to the "just blame the pilot(s)" syndrome we complain the FAA is too quick to do.

:cool:

Not what I meant, maybe I used the wrong terms to express myself. I meant that we can see if the computers who predict these outings were correct or not and just because 2 planes had the same issue doesn't mean they both didn't do the preflight correctly. What if they both used foreflight so they didn't have a need to check anything else? It's not always about the pilots being wrong, these things might bring up forflight for example being wrong.
 
Walt. To make sure I'm understanding you correctly; If I select an LPV approach and the GPS tanks, the 650 will automatically kick over to an ILS for the same runway?

I've got a ton of time with a G-1000 and don't recall ever discovering this. Have I just not got deep enough in the book or is this specific to the 650/750?

I did not mean to imply that if you lose GPS it will auto switch to an ILS on it's own, but when a runway has both an ILS and a GPS though I try to make it a habit to have the ILS tuned so if I lost the GPS I could manually switch over by hitting the CDI button and grab the needles.

My point was have an ILS as a backup makes me feel good.
 
Why not dual source?

Walt,

I'm interested in why not recommend the GTX 375 paired with a GNC 255A Nav/Com. This would provide dual nav along with dual source and is several AMU's cheaper than the GTN 650.

I realize the 650 has a few more bells and whistles that the GTX 375 doesn't but what am I missing because I haven' seen this combo in panels. I'm about ready to order my panel and can't decide which path to take regarding this very topic.

Your thoughts?

Thanks

Mark
 
My point was have an ILS as a backup makes me feel good.
+1
Having a VOR/ILS as backup also makes me feel good about how I equipped my airplane. Oh, here in NE Florida the US Navy jams GPS signals once in a while during aircraft carrier operations off the coast. They are NOTAM'd but I wouldn't be surprised some are done by "accident". Caveat Pilot! :cool:
 
Last edited:
Walt,

I'm interested in why not recommend the GTX 375 paired with a GNC 255A Nav/Com. This would provide dual nav along with dual source and is several AMU's cheaper than the GTN 650.

I realize the 650 has a few more bells and whistles that the GTX 375 doesn't but what am I missing because I haven' seen this combo in panels. I'm about ready to order my panel and can't decide which path to take regarding this very topic.

Your thoughts?

Thanks

Mark

Your combo comes out a little less (don't forget to add the 2nd comm) but it also has fewer features such as bigger screen, VNAV, integrated operation between GPS/ILS transitions etc..

Once you fly with waypoint crossing altitudes tied to VNAV you'll wonder how you ever lived without.

I also think there are going to be more features coming to the new GTN Xi series that you won't have in the 'budget' navigators.

A valid point about redundancy but the GTN units are basically 3 self contained units in a single box so you can have a GPS failure that won't take down the com/nav side and vice versa.
 
Last edited:
RAIM

While rare, RAIM availability (or lack thereof) is an occasional short term operational issue in AUS. No WAAS (yet)
We preflight check availability and pre approach too on the navigator just to be sure.
It’s never affected an actual flight planned arrival for me and the gaps are usually short lived.
Maybe it’s because of no WAAS. Maybe it’s southern latitudes. I dunno.
I’ll also observe that I’ve flown with pilots who don’t check it and it wouldn’t surprise me if some routinely don’t.
 
Last edited:
Sooo..... that was kind of near Kennedy space center around the time Air Force one was in the area, getting ready for space X launch. Self defense? Hmmm.
 
+1 for VAL INS429

I hung an INS429 below my panel in front of the stick. It's low cost insurance against GPS signal loss, GPS failure or EFIS failure. And, because it's a stand alone unit, about all you have to do is provide power, ground and antennas.

I removed a VAL Nav2000 which never worked right for VOR reception and replaced that with a King DME from eBay. It makes VOR/ILS navigation much easier and the used DME's are also easy to install and quite reasonable. (I should qualify that I had the right size slot with power, ground and coax for the Nav radio in place.) John
 
Last edited:
Back
Top