GPS Testing out West

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Walboy

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Walboy
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it means pretty much what it says, GPS may not be available within that area. Yes it affects airplanes though usually briefly and temporarily, and I've only seen that a few times.
it has to do with what they're testing. GPS isn't unreliable, what they're doing is making it unreliable if it's like some of the other notams I've seen closer to salt lake city. I don't have the verbage on that one handy to see if it's worded the same.
 
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So how does that work when a 146(?) GPS is certified as the sole means of navigation under IMC?
 
Those messages have been going on for years here, occasionally the GPS will actually not work (we are told it is the military testing, or practicing jamming?) and when it is out, you will hear airplane after airplane make the required call to ATC about it, I think most say "dead reckoning" as that is what the FMS/FMC says.
 
I have had flights with extensive loss of GPS positioning during NOTAMS, some of it with errant data, even though the satellite signals were strong.

So far all in remote SW locations.
 
Well, alternate means of navigation is not required with a WAAS GPS, but it might be a good idea if there is a NOTAM like that in the area.

I take that NOTAM to mean that direct-to routing might not be a good idea, and an alternate with a non-GPS approach might be advisable.
 
What I don't understand is why they don't just test out in the middle of the Pacific Ocean....:dunno::dunno::dunno::dunno:
 
The military seems to have to practice GPS jamming a lot in the White Sands area. Believe me, it works.

My gps, 500 series garmin just does dead reckoning for me until the gps signal comes back, VFR or IFR.

Going to Las Cruces one day and the signal was jammed. I was vfr so I just descended below the mountains until their jamming signal was blocked and I had my gps back.

I do not recommend going below the mountain tops to folks that are not able to do so safely.
 
Don't they realize that once ATC is dependent on ADS-B this sort of testing will be even more disruptive?
 
dans2992 said:
Don't they realize that once ATC is dependent on ADS-B this sort of testing will be even more disruptive?
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It's only disruptive if you treat GPS as invulnerable.

There are other ways it might fail besides jamming (intentional or otherwise). A strong solar flare could do it, for instance.

If the FAA truly is treating it that way (which I very much doubt), that's the FAA's fault.
 
MAKG1 said:
It's only disruptive if you treat GPS as invulnerable.
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Ha.

Look at some of the "children of the magenta line" pilots who mock the old farts who espouse pilotage and actual chart reading as a backup.

"But I've got 3 i-toys in the plane. I don't need to learn this VOR plotting crap."
 
ElPaso Pilot said:
I have had flights with extensive loss of GPS positioning during NOTAMS, some of it with errant data, even though the satellite signals were strong.

So far all in remote SW locations.
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Not so remote SW locations. Reading the [almost] continual notams from NM and white sands, the disruption can be as far north as the Colorado/Wyoming border.

Once again, the time zone no one gives a flying fig about.
 
VORs are out even more often than GPS. Then again, they usually all aren't down at once.
 
Walboy said:
What is the typical duration of the loss of GPS signal? seconds? minutes? hours?

I remember reading something in my GPS manual about dead reckoning in the event of GPS signal loss. I need to reread that section and make sure I understand it.

Is there continual GPS testing like this in the eastern portion of the country?
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A older cross-post of mine from the Red Board, with a data dump from my 296.

How about 300 miles of bad GPS, including seeing a climb to 55,000' at 3000 knots. Nice performance, eh? :goofy:

Oh, and the GPS won't ded reckon here. I had a GPS signal ... it just wasn't correct. Think old fashioned, finger on the sectional ded reckoning.

At some point west of Lawton / Ft. Sill OK I noticed my GPS ground speed was approaching 3000 knots. Not bad in a Bo with a 30 knot headwind. Flipping through the screens, I got to see the altimeter winding up through FL 550.


8:05:08 AM 6592 ft 3135 mph 231° true
8:05:16 AM 6592 ft 3449 mph 229° true
8:05:25 AM 14,456 ft 3300 mph 229° true
8:05:34 AM 18,989 ft 3288 mph 229° true
8:05:47 AM 25,632 ft 3278 mph 229° true
8:06:02 AM 33,498 ft 3268 mph 229° true
8:06:13 AM 39,306 ft 3260 mph 230° true
8:06:24 AM 45,201 ft 3248 mph 230° true
8:06:35 AM 51,059 ft 3238 mph 230° true
8:06:44 AM 55,860 ft

It did not work properly for another 300 miles. Coincidently, just outside of Roswell, NM, it started running again like nothing was ever wrong.
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I think panel mount units are supposed to be able to identify bad GPS data better than portables, right? Fact or fiction?
 
ElPaso Pilot said:
Ha.

Look at some of the "children of the magenta line" pilots who mock the old farts who espouse pilotage and actual chart reading as a backup.

"But I've got 3 i-toys in the plane. I don't need to learn this VOR plotting crap."
Click to expand...



Hard to do pilotage at FL250, much less a VFR chart.
 
Zeldman said:
Hard to do pilotage at FL250, much less a VFR chart.
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Referring to the recurring threads from student pilots who complains about not being able to use their electronic gizmos during training... Or relying on them 100% afterwards.

I recall one who when challenged said he didn't need to learn alternate navigation as his iPad backup was his iPhone...and GPS doesn't fail anyway.
 
KSCessnaDriver said:
Where in the US are you outside of radar coverage at FL250? If you were, it might be a big deal, otherwise, who cares
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On April 16th of this year I was flying over Northern Nevada at 28,000 feet on my way to SoCal when I lost all GPS signal. It lasted twenty minutes. I have at least five GPSes, two of them WAAS certified units. None of them so much as received a single satellite. Fortunately I also have two Nav radios and surprisingly these work too if one is properly trained in the art of flying the green line so it was a non event. No DME required.

The only reason I remember the date is because it was the day after sending a gut-wrenchingly large check to the IRS and I remember thinking the GPS network is one of the few things I don't mind paying for and I was ****ed it failed me within 24 hours of sending in my money.

GPS NOTEMs are common in the Intermountain West. Being unable to navigate via GPS is pretty rare, but it does happen from time to time.
 
Wingsofglass said:
On April 16th of this year I was flying over Northern Nevada at 28,000 feet on my way to SoCal when I lost all GPS signal. It lasted twenty minutes. I have at least five GPSes, two of them WAAS certified units. None of them so much as received a single satellite. Fortunately I also have two Nav radios and surprisingly these work too if one is properly trained in the art of flying the green line so it was a non event. No DME required.

The only reason I remember the date is because it was the day after sending a gut-wrenchingly large check to the IRS and I remember thinking the GPS network is one of the few things I don't mind paying for and I was ****ed it failed me within 24 hours of sending in my money.

GPS NOTEMs are common in the Intermountain West. Being unable to navigate via GPS is pretty rare, but it does happen from time to time.
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The question wasn't if you are outside of GPS coverage, it was radar coverage. If your GPS goes tits up at FL250, advice ATC and ask for a vector, problem solved.
 
MAKG1 said:
It's only disruptive if you treat GPS as invulnerable.

There are other ways it might fail besides jamming (intentional or otherwise). A strong solar flare could do it, for instance.

If the FAA truly is treating it that way (which I very much doubt), that's the FAA's fault.
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And satellite killing missiles according to China !!!
 
The net result of these notams saying something may not work when usually it does work....is over time, to deaden one's senses to the existence of notams.
 
Walboy said:
It has occurred to me that I am reading the poorly worded NOTAM incorrectly. I am assuming it means the unreliable signal begins at 50' AGL and extends upward to FL400 within a 251NM radius. Doesn't make sense that the signal loss would be below 50'. I'm not sure what FL400-UNL means. I will probably call an AFSS briefer and ask them to help me understand the NOTAM.
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I reproduced the relevant paragraph of that NOTAM for reference. I interpret it as follows:

First of all, "FL400-UNL" means "from flight level 400 to unlimited," and refers to an altitude range that starts at flight level 400 and goes up from there to infinity. In other words, there is no upper limit on the altitude range being referred to. That altitude range applies as far out as 454 NM radius from the center of the affected area. The altitude stepdowns are telling you that as you get closer to the center of the affected area, you could experience problems at lower and lower altitudes. With regards to the 50 feet AGL, they're not saying you could be affected below 50 feet, they're saying you could be affected as low as 50 feet. That may be unlikely if there is intervening terrain, but remember, they're saying that the testing may result in problems within that area, not that it definitely will. It would not be feasible for them produce a map of the potentially affected area that went into enough detail to take into account all of the varying terrain between the test site and the location of your aircraft.

D. NOTAM INFO: NAV (CHLK GPS 15 - 07) GPS (INCLUDING WAAS, GBAS, AND ADS - B) MAY NOT BE AVAILABLE WITHIN A 454NM RADIUS CENTERED AT 360822N1173846W (BTY 214059) FL400 - UNL DECREASING IN AREA WITH A DECREASE IN ALTITUDE DEFINED AS:
430NM RADIUS AT FL250,
359NM RADIUS AT 10000FT,
301NM RADIUS AT 4000FT AGL,
251NM RADIUS AT 50FT AGL.​

I might plan on flying a GPS approach in the potentially affected area, but I would be sure to watch for RAIM error messages, and I would be prepared to fly a non-GPS approach, which might necessitate diverting to a different airport.
 
I have a different question. Does anyone know what the point of these tests is? The government has no need to terrestrially jam GPS signals. It has the ability to simply render the civilian signal unusable in an area. It would seem much more likely that they'd want to block the GLONASS signal, which they have no control over, but that operates on different frequencies.
 
In the past, the ones centered on Alamagordo are there because there's a large lab that can simulate the entire GPS cluster for tech testing.

Ones centered on Southern Colorado were one defense contractor testing their jammers, and the ones centered on the southeastern U.S. were another.

The lab generally isn't much of a threat but they're always posting notams in case someone opens the damn doors at the wrong time.

The jammers are more of a problem.

What they're up to with these latest ones, I can't tell ya.
 
denverpilot said:
In the past, the ones centered on Alamagordo are there because there's a large lab that can simulate the entire GPS cluster for tech testing.

Ones centered on Southern Colorado were one defense contractor testing their jammers, and the ones centered on the southeastern U.S. were another.

The lab generally isn't much of a threat but they're always posting notams in case someone opens the damn doors at the wrong time.

The jammers are more of a problem.

What they're up to with these latest ones, I can't tell ya.
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Good info. We get these in Denver seemingly all the time.

The NOTAM language in most cases is describing what amounts to a cone of interference. It's small at the source on the surface and radiating outward and upward from there.

But I agree with the OP that these NOTAMs are annoying because they are so frequent.
 
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