GPS backup

Someone other than Salty - he didn’t say this said:
Isn't WAAS stand alone? Then no "approved backup" is required, and anything is better than nothing.
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WAAS is to create a signal enhancer, signal correction data - not a GPS signal. There are 38 ground based WAAS stations in the US, Canada, Mexico, HI. They don’t send a GPS signal out, just instructions to correct the existing GPS signal. That signal goes up to the geo sync satellite, which is what our GPS units talk to to get the correction signal.

So if GPS is jammed, the WAAS isn’t able to help.
 
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WDD said:
WAAS is to create a signal enhancer, signal correction data - not a GPS signal. There are 38 ground based WAAS stations in the US, Canada, Mexico, HI. They don’t send a GPS signal out, just instructions to correct the existing GPS signal. That signal goes up to the geo sync satellite, which is what our GPS units talk to to get the correction signal.

So if GPS is jammed, the WAAS isn’t able to help.
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I don’t know what happened, but I never posted what’s in the quote box with my name on it.
 
Salty said:
I don’t know what happened, but I never posted what’s in the quote box with my name on it.
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That’s just odd. You indeed didn’t post that. Someone else did. How was that even possible?
 
Salty said:
I don’t know what happened, but I never posted what’s in the quote box with my name on it.
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Yeah! That was MY post! But you might agree that with 592 AM radio stations in Florida it would be nice to have a simple device that keeps a running estimate of your position by utilizing them as a backup to GPS. https://radiostation.info/am/florida/
 
dtuuri said:
Yeah! That was MY post! But you might agree that with 592 AM radio stations in Florida it would be nice to have a simple device that keeps a running estimate of your position by utilizing them as a backup to GPS. https://radiostation.info/am/florida/
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I guess a DF antenna could be installed for that purpose. The receiver would need to have a database of station frequencies and locations. The receiver would need to know the last GPS position in order to differentiate between broadcast stations on the same frequency.
 
midlifeflyer said:
Sure, If you have nothing else, all bets are off and the rules don't matter.
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Your comment and article earlier prompted me to go back and read the AFMS for my GTN650. Thank you.

Amazingly, the Abnormal Procedures section describes the outcomes when there’s a loss of GPS/SBAS Nav signal and what actions to take; same for approach downgrades.
 
TCABM said:
Amazingly, the Abnormal Procedures section describes the outcomes when there’s a loss of GPS/SBAS Nav signal and what actions to take; same for approach downgrades.
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Not so amazing since "here is where we think you are" mode has been there since the GNS-WAAS models
 
Palmpilot said:
The receiver would need to know the last GPS position in order to differentiate between broadcast stations on the same frequency.
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Brainstorming with you, why is GPS needed? Each location, say pixel on a map of, say, Florida, would have one set of theoretical bearings that should exist over that point. So, the device would only need to find the pixel with the highest number of matching bearings — and there's where you probably are. No?
 
MikeNY said:
If useful as heads up,
FLIGHT ADVISORY - GPS Interference Testing - Patuxent River (29 July-16 August)
(weekdays, 7am-11am lcl)
"testing ... may result in unreliable or unavailable GPS signal"

View attachment 131736
"This notice is being sent to you because you selected "Selected ATC Notices" in your preferences on FAASafety.gov."
[faasafety.gov > My Preferences and Profile > Email Notification Preferences]
... or full list under Resources > Notices

Addition to checking NOTAMs, RAIM check, etc., 'email notification' for Flight Advisory, (VIP TFRs, etc.) can be helpful as ... heads up.
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GPS interference testing in a similar time frame in the Fort Drum area of NY, which will potentially affect Syracuse and points south in Central NY depending on altitude.
 
Half Fast said:
So please explain how that AM broadcast station will let you fly an IFR approach, unless it happens to have its broadcast tower located on the airport runway, which seems unlikely.

Can you triangulate between multiple broadcast stations? Yes, if you have some sort of steerable antenna, but the accuracy probably won’t be sufficient for an IFR approach, and you will want some automation that doesn’t exist yet. If you have to develop something new, maybe it makes sense to use a better method.

So yes, the geeks are indeed “ruining” a concept that doesn’t work and suggesting concepts that might.
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Hmm, there were approaches before VORs and TACAN (which includes DME).

NDB approaches did not require the station to be ON the field. Just fairly nearby.

Multi station triangulation would certainly allow you to shoot an approach. NO, not to ILS minimums, but at least better than no approach.

And an ADF did the DFing without anything complicated.

Many years ago, some drafted an approach plate based on a commercial broadcast station to a local airport that had no approaches. It looked like the real thing. I don't KNOW that anyone ever flew that approach for real, but I know that it was flown for fun in VFR conditions.
 
dtuuri said:
Brainstorming with you, why is GPS needed? Each location, say pixel on a map of, say, Florida, would have one set of theoretical bearings that should exist over that point. So, the device would only need to find the pixel with the highest number of matching bearings — and there's where you probably are. No?
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The problem is that each frequency is used by multiple stations around the country and around the world. It sounds like your database would need to include a unique set of bearings, frequencies, and hours of operation for every pixel on the chart. Maybe the size of the database could be made more manageable by limiting the scan to "clear channel" frequencies.
 
William Pete Hodges said:
Not too long ago I flew through an area where GPS coverage was interrupted or possibly jammed for about ½ hour. I continued navigating by dead reckoning and dialed up the nearest VOR to use as a reference. Fortunately there was an active VOR along my route, but VORs are being decommissioned every day and the number remaining is dwindling fast along with their NDB counterparts.

The GPS network is a remarkable system allowing navigation flexibility and ease of use, but it is only as good as the signals available. My recent flight proved to me it's vulnerability to be interrupted. My situation occurred mid flight so it was easy for me to maintain my flight but what if it had happened during IMC conditions or during an IFR approach?

I have been doing some research into this and I think the FAA needs to rethink this policy and add back some ground based radio navigation systems especially NDBs. Why NDBs? NDBs are the least expensive ground based navigation system available. They are easy to maintain as they require minimal maintenance. In the cockpit they are less precise and harder to use than VORs but they have the advantage of using not only dedicated NDBs but also AM radio station signals that require zero maintenance costs incurred by the FAA.

In short I think the FAA should reevaluate their position on NDBs and reinstate many of them for use as navigation aids as a backup to GPS. I realize I am likely in the minority in this line of thinking, but I am intending to reinstall an ADF in my airplane for this reason.

I am interested on your thoughts on this subject. What do you think?
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How would the children of the purple line learn how to naviagate using an NDB?
 
Clip4 said:
How would the children of the purple line learn how to naviagate using an NDB?
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Ahhh, but the children of the purple are learning to use bearing pointers - standard with glass. Not as well as they should, and maybe not even for the checkride, but they are learning.
 
Palmpilot said:
The problem is that each frequency is used by multiple stations around the country and around the world. It sounds like your database would need to include a unique set of bearings, frequencies, and hours of operation for every pixel on the chart. Maybe the size of the database could be made more manageable by limiting the scan to "clear channel" frequencies.
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Easier to maintain position with GPS and confirm with ADF cross bearings. And if GPS goes away (and it knows when it does) you have a known starting position.

DME/DME or VOR/DME is easier.
 
midlifeflyer said:
Ahhh, but the children of the purple are learning to use bearing pointers - standard with glass. Not as well as they should, and maybe not even for the checkride, but they are learning.
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Using a pointer and tracking is a bit of a different skill set.
 
Pinecone said:
DME/DME or VOR/DME is easier.
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Some agree, some don’t. But in any case VOR and DME stations are going away because of cost, maintenance and reliability issues, etc. So I would say a GPS back up isn’t going to use VOR / DMEs.

And that doesn’t help you with shooting an approach in IMC what with ILS transmitters also being shut down for the same reasons.

………………..
BTW - If the military is jamming GPS signals to deny others the ability to precisely guide/navigate, wouldn’t they also have to learn how to and practice jamming the back up system?

A back up system would also have to be able to survive solar weather. And MicroSoft security upgrades.
 
WDD said:
BTW - If the military is jamming GPS signals to deny others the ability to precisely guide/navigate, wouldn’t they also have to learn how to and practice jamming the back up system?
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That's not what's happening within CONUS. Typically the US military is testing whether US equipment can function properly in a GPS-denied environment, such as an enemy using jammers. All the outages I've been involved with have been very brief, like a few minutes, even though a NOTAM might give an hour or two.

As an example, suppose the AF is testing a weapon. They might have a range launch window of two hours, even though the engagement will only last a few minutes. The warning of GPS outage has to cover that entire window, but in reality the jamming will begin shortly before launch and end immediately after the flight is terminated.

Without getting into too many specifics, a missile will often use GPS to get within a capture "basket" inside of which the weapon will engage with IR or radar or the end game. The jammer is located near the target, so the weapon has to be capable of lifting the GPS signal out of the jamming noise or rejecting a spoofed signal until it flies within range for the terminal guidance to take over. Often the missile is flying inertially and using GPS signals whenever it can get them to inform the inertial guidance.

There's a lot more complexity, both technical and tactical, to all of this but it wouldn't be appropriate to dig deeply into it all on the forum.
 
WDD said:
Some agree, some don’t. But in any case VOR and DME stations are going away because of cost, maintenance and reliability issues, etc. So I would say a GPS back up isn’t going to use VOR / DMEs.

And that doesn’t help you with shooting an approach in IMC what with ILS transmitters also being shut down for the same reasons.
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They are shutting down VORs, not DMEs. MUCH small footprint and less maintenance.

Airlines and some bizjets use DME/DME/INS or DME/DME/DME as primary nav.
 
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