GPS backup

William Pete Hodges

William Pete Hodges

Line Up and Wait
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Mar 6, 2020
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598
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Virginia
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Petehdgs
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?
 
William Pete Hodges said:
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?
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I don’t see how NDBs solve the problem for you.

The NDB isn’t going to let you do an RNAV approach, and mid-flight you can always explain the situation to ATC and ask for a vector if you don’t already have a good heading to maintain.
 
William Pete Hodges said:
I think the FAA needs to rethink this policy and add back some ground based radio navigation systems especially NDBs. Why NDBs? ... 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.
Click to expand...
I've said it before and said it here too, but now I can't find the posts. Who needs the FAA for this? Just find a radio guy who believes in it. Why can't a receiver scan the spectrum of low frequencies, automatically triangulating position bearings? Surely the transmitter locations are in a database somewhere at the FCC. The greater number of bearings taken, the more accurate the position estimate. Who needs the FAA for that? We're talking "emergency backup chute" here. I'm with you and I hope somebody invents it and sends us each a substantial gratuity for helping make them rich. :)
 
If you really want an on-board backup besides your compass+DG, I’ll offer three words: inertial navigation system.
 
If the FAAs reason for dropping VORs is maintenance (do they need that a lot ?) - an NDB should be cheap and simple to maintain. Just a low-frequency transmitter with a suitable antenna. Check that it's on the correct frequency, check power level, inspect the antenna = good to go!
[I like the other idea that's been tossed about - set up a piece of avionics (kind of a modern ADF) that would use FM broadcast: lots of power, fixed locations, well known database that doesn't change very often, VHF so lightning/atmospherics less of an issue. By multiple bearings to several stations the location could be fairly closely determined.]
 
dtuuri said:
I've said it before and said it here too, but now I can't find the posts. Who needs the FAA for this? Just find a radio guy who believes in it. …
Click to expand...

There’s a ton of cheap micro INS chips out there today that would only need a little integration to give you a more robust GPS/INS solution.

Those pesky TSOs stand in the way, but they’re being used in commercial UAVs already.
 
TCABM said:
There’s a ton of cheap micro INS chips out there today that would only need a little integration to give you a more robust GPS/INS solution.

Those pesky TSOs stand in the way, but they’re being used in commercial UAVs already.
Click to expand...

A portable INS that ties into your tablet much like a Stratus GPS might be nice.
 
Half Fast said:
A portable INS that ties into your tablet much like a Stratus GPS might be nice.
Click to expand...

Or embedded in every panel nav or sent to a standalone panel indicator.

I’m all about tablets/EFBs to provide SA, but in IMC, I want as much displayed on the panel as possible.

I forget where, but the FAA has a recommendation for IMC flight that all primary and supporting indictators be within 8” of the attitude indicator to minimize head movement relative to scan.

The more I jump between analog/semi-glass, and full glass, the more I understand that philosophy.

Second, the real estate on a tablet is tiny compared to a standard round gauge. Sure, one can argue a portable HSI presentation overcomes that, but you’ve still got tach and/mp and the turn coordinator that’s not on the best of the tablet HSIs.

Either way though I’d expect the EAB crowd to have solved for this by now.
 
StraightnLevel said:
OK....but if GPS goes out for everyone and nobody else in the air has a backup, how many aircraft does ATC have the bandwidth to support?
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All the ones on an instrument flight plan. VFR flights can use pilotage, and can get ATC on a time-permitting basis. Same as always.
 
TCABM said:
Or embedded in every panel nav or sent to a standalone panel indicator.

I’m all about tablets/EFBs to provide SA, but in IMC, I want as much displayed on the panel as possible.

I forget where, but the FAA has a recommendation for IMC flight that all primary and supporting indictators be within 8” of the attitude indicator to minimize head movement relative to scan.

The more I jump between analog/semi-glass, and full glass, the more I understand that philosophy.

Second, the real estate on a tablet is tiny compared to a standard round gauge. Sure, one can argue a portable HSI presentation overcomes that, but you’ve still got tach and/mp and the turn coordinator that’s not on the best of the tablet HSIs.

Either way though I’d expect the EAB crowd to have solved for this by now.
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Yes but all that requires certified equipment. It’d take the FAA more than a decade to bless it. Portables for emergency backup could be done without all the FAA hoops just like portable GPS equipment.
 
Half Fast said:
Yes but all that requires certified equipment. It’d take the FAA more than a decade to bless it. Portables for emergency backup could be done without all the FAA hoops just like portable GPS equipment.
Click to expand...

Collins has a gps-aided micro INS out now for the homebuilt crowd now that continue to perform in the absence of GPS and connects using standard connectors and protocols.
39866887c03901084aa9c537afec927f.jpg
 
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.
Click to expand...
True, but there is a commitment to have enough VOR left (just under 600, and hopefully operating) to get you somewhere there is a usable ground-based instrument approach, even if NORDO. With the new VOR Low and VOR High service volumes (basically increasing the service volumes 5,000' above the station from 40 to 70 NM), there are probably few areas where this will be a problem.
 
Interesting. I am very recently getting back into flying after a ten-year hiatus. Sold my Ercoupe 10 years ago and just bought another (yeah, I do like this platform for low and slow along the coast where we live). So, with the potential loss of GPS and my penchant for 100-200 mile breakfast or hamburger flights, I just (last week) bought a good old fashioned paper Sectional Chart for our area. It was $14.66 (from Amazon, of course) and will provide a bit of peace-of-mind, just in case.
 
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When I fly cross country, I always file IFR. And during the flight, I keep a nav radio tuned to the nearest relevant VOR.
 
Interesting topic
1) Like stated above, why not have a device that can pick up multiple frequencies and triangulate your position? Make the FAA talk to the FCC, find out where ground based towers are and what frequencies, keep the map updated, and let your nav computer figure it out.

2) Make a cheaper VOR. The reason these things are going out is because they are old and use old expensive (hey Fred, what is this glowing tube like thing in this here control box?). Got to be a way to make them more robust and less expensive to operation.

3) Even at 10,000 feet my adult kids track me when I fly up to see them. On "Find my I Phone". Actually easier to use than flight tracking software. So let's incorporate that tech.
 
BaltimoreBill said:
Interesting. I am very recently getting back into flying after a ten-year hiatus. Sold my Ercoupe 10 years ago and just bought another (yeah, I do like this platform for low and slow along the coast where we live). So, with the potential loss of GPS and my penchant for 100-200 mile breakfast or hamburger flights, I just (last week) bought a good old fashioned paper Sectional Chart for our area. It was $14.66 and will provide a bit of peace-of-mind, just in case.
Click to expand...
Congrats on getting back! And hey, if paper works for you, use it. But once you load the latest sectional chart in your I Pad/whatever, it's there and won't be affected by any rare GPS whatnot. FWIW - as much as I am a magenta line devotee, I use a LOT of paper when preparing and in the air.
 
StraightnLevel said:
Why keep NDB as opposed to VOR? It seems to me that one good ground-based backup makes sense, so perhaps the first debate should be which one to keep.
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NDBs are MUCH cheaper to install, operate, and maintain, on the order of 10:1. If you are looking for an inexpensive backup to GPS they give a lot bang for their cost.
 
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?
Click to expand...
I've posted this exact sentiment several times here over the years.
It'll never happen, me thinks,
but as a thought experiment it seems like a good idea to me. Seems like about the only system that is dirt simple and is probably very cheap.

As I see it...and this is all speculation and intuition-based, from someone who is not exactly an electronics expert...
VOR's seem like extremely complex ground stations that require what I reckon is substantial upkeep. They offered significant useability advantages though over NDB's (I busted my initial instrument ride on an NDB approach, so yes I appreciated VOR's back in the day!) but as a backup system for GPS it feels like an expensive and very complicated dinosaur.

Other back-up solutions (such as INS), it seems to me would require on-board systems that would probably be expensive and would require maybe significant calibration and checks.

I could be very wrong, but based on my intuition I'm assuming that little very low-power modern versions of NDB stations could be installed very cheaply.
and with modern electronics, I'd think that the ADF receivers could be cheap, small, and lightweight
I would envision the easiest approach would be to primarily install the NDB's on airports. Seems like the location on the field wouldn't be all that critical, given their non-precision nature. A small box mounted on the roof of the FBO, or up on the rotating beacon tower, or wherever really....

As I recall, most of the mental gymnastics with them came when they were located off-field. When they were on the airports, shooting the approach was a breeze! Locating them on the airports would make it an easier almost idiot-proof back-up for pilots who are used to following the magenta line. And that is based on the idea of an old-fashioned ADF needle
If they were instead incorporated into the modern moving map big screen GPS computer boxes, all sorts of RNAV magic could be done with the signals.

A low-power and low-range NDB placed on most airports would still give a pretty extensive network, and if there were small gaps of signal loss between them they could be bolstered with an occasional en route NDB where airports are spaced far apart. and/OR, because it's a last-ditch back-up, what would be wrong with flying ded-reckoning for a bit between, like in the old days?
 
I used to fly a plane that had a Garmin 530w that provided ded reckoning heading when the military was practicing their GPS jaming. Which happens a lot here in the southwest coming from the White Sands Restricted area.

I learned to defeat the GPS jamming by flying below the mountain tops...(but don't let that leak out...)
 
StraightnLevel said:
Perhaps, but as a new pilot I can say that I've never worked with NDB at all. It's no longer required in training, and it's a lot more difficult to use than VOR (in the cockpit).

When you're suddenly shifting to your backup nav, ease-of use is really important. VOR with a standard 430 or 530 is really simple - just tune to the nearest VOR frequency and find the right radial.
Click to expand...
I think the idea is that the "new" NDB would not have the pilot interact with it. It would just be a signal generator the Nav unit (GTN, etc.) would pick up, do the calculations, and then present you with the results as it does now with the GPS signals.
 
StraightnLevel said:
Perhaps, but as a new pilot I can say that I've never worked with NDB at all. It's no longer required in training, and it's a lot more difficult to use than VOR (in the cockpit).

When you're suddenly shifting to your backup nav, ease-of use is really important. VOR with a standard 430 or 530 is really simple - just tune to the nearest VOR frequency and find the right radial.
Click to expand...
most of the mental gymnastics came when shooting an approach to an airport or do something else with an NDB that was located someplace off the airport.

When the NDB is on the field, it was dirt simple. For VFR, the needle points to the airport. For an approach, there's a little mental work to make sure that you're on the correct 'radial', and you've got to juggle time and altitude, but it was still very simple.

And I reckon if the receivers were built into the GPS box, most or all of that math could be done for you
 
dtuuri said:
I've said it before and said it here too, but now I can't find the posts. Who needs the FAA for this? Just find a radio guy who believes in it. Why can't a receiver scan the spectrum of low frequencies, automatically triangulating position bearings? Surely the transmitter locations are in a database somewhere at the FCC. The greater number of bearings taken, the more accurate the position estimate. Who needs the FAA for that? We're talking "emergency backup chute" here. I'm with you and I hope somebody invents it and sends us each a substantial gratuity for helping make them rich. :)
Click to expand...

You can buy that off the shelf.

previously:
https://www.pilotsofamerica.com/com...’-incidents-increase.146047/page-2#post-3487143
 
TCABM said:
Collins has a gps-aided micro INS out now for the homebuilt crowd now that continue to perform in the absence of GPS and connects using standard connectors and protocols.
39866887c03901084aa9c537afec927f.jpg
Click to expand...
Which means someone, somewhere, will put together a package for a tablet. Same idea as the stratus software with a couple SDRs for a Rasperry Pi.
 
StraightnLevel said:
Perhaps, but as a new pilot I can say that I've never worked with NDB at all. It's no longer required in training, and it's a lot more difficult to use than VOR (in the cockpit).

When you're suddenly shifting to your backup nav, ease-of use is really important. VOR with a standard 430 or 530 is really simple - just tune to the nearest VOR frequency and find the right radial.
Click to expand...
Didn't learn about NDB? Just tune to your local AM station and practice. Of course that assumes you've got an ADF in the airplane. I keep my ADF so I can listen to the ball games. Plus once I get near the KOA tower (630 on your AM dial) I can probably see the approach to rwy 28 at KAPA. Park the cherokee and uber home.

Update: 850 on the AM dial.
 
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TCABM said:
Collins has a gps-aided micro INS out now for the homebuilt crowd now that continue to perform in the absence of GPS and connects using standard connectors and protocols.
39866887c03901084aa9c537afec927f.jpg
Click to expand...

Size 4.5 x 2 x 1 in
Weight 0.25 lbs
Enclosure Aluminum

Hm....awful lot like a stratus but the connectivity is another issue. I wonder what the positioning requirements are compared to a portable AHRS.
 
murphey said:
Size 4.5 x 2 x 1 in
Weight 0.25 lbs
Enclosure Aluminum

Hm....awful lot like a stratus but the connectivity is another issue. I wonder what the positioning requirements are compared to a portable AHRS.
Click to expand...

They’ve got a data sheet that may help answer that; the first thing I noticed is an internal magnetometer and possibly a baro input.

 
If IFR in radar contact, your GPS backup is your COM. ATC can give vectors to get you where you need to go. GPS approach backup is your nearest LOC/ILS or (if you can find one) VOR approach.

Having flown extensively with LORAN-C back in the day, it was a perfectly fine ground-based navigation system, operating on a similar principle but completely different frequencies than GPS. I think its successor, e-LORAN was even better. I still have in my basement an Apollo LORAN-C unit that became a paperweight when they decommissioned LORAN-C. The advantage of LORAN is that you don't need hundreds of stations to maintain a navigation network. Can it be jammed? Sure. But better to have two different nav systems so if one is down, the other is usable. One could even envision hybrid units that use both signals.Probably not going to happen, though.

But TBH, Victor airway navigation in the northeast right now is fairly impractical. If a VOR isn't decommissioned, it is broken or "permanently" out of service. Usually "you can't get there from here" by VOR.
 
StraightnLevel said:
OK....but if GPS goes out for everyone and nobody else in the air has a backup, how many aircraft does ATC have the bandwidth to support?
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You are only looking at this from a GA perspective. The FAA looks at it from a national airspace system perspective and most of the users of the NAS have a backup to GPS--DME/DME/IRU.

The minimum VOR network is designed to support DME/DME/IRU.
 
Half Fast said:
If you really want an on-board backup besides your compass+DG, I’ll offer three words: inertial navigation system.
Click to expand...

I’ll offer a one word solution: Omega.

I used it while in the Navy. But it has its quirks, too.

-Skip
 
Larry in TN said:
You are only looking at this from a GA perspective. The FAA looks at it from a national airspace system perspective and most of the users of the NAS have a backup to GPS--DME/DME/IRU.

The minimum VOR network is designed to support DME/DME/IRU.
Click to expand...
Thank you. I always wonder why this isn't brought up in these sorts of discussions.

A backup network for GPS already exists, it's DME/DME (with or without IRU). As VORTACs and VOR/DMEs and even TACANs are decommissioned, very often the DME portion of the facility is left in place, specifically to support DME/DME operations.

Since the technology for DME/DME positioning already exists in thousands of airliners and other turbine equipment (even smaller stuff like the King Air I fly), I think it would be a pretty simple matter for it to be adapted for light GA. I don't see why there couldn't be a GPS receiver with built-in DME/DME backup. It's certainly technologically possible - companies literally already make them. Just adapt the form factor.
 
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