GPS Anomalies

heavymetal · Post by **heavymetal** » Thu Apr 20, 2006 8:29 pm

I was fired up on tha ramp today while the Herc was doing drops over the airport and noticed some strange things with the Garmin 430. First of all after start up the GPS took a good 30-45 seconds longer than usual to position itself and once I did I checked RAIM, checked satellite coverage etc and all checked fine. About 15-20 seconds before the Herc passed over head again we lost satellite integrity for another 15 seconds.

Has anyone out there heard if any of the equipment used on the Herc or any of the stuff they drop out of the back transmits radio signals that might interfere with GPS signals? I realize it might be a stretch, but I have never lost integrity of signal with the Garmin 430 before and all functions tested normal on the box as they had the previous flights of the day and FSS had no reported anomalies by any other aircraft in the area.

Cat Driver · Post by **Cat Driver** » Thu Apr 20, 2006 11:24 pm

heavymetal:

Is it possible that random gravity surges could be the culprit?

You know those gravity surges that results in really badly bounced landings?

Cat

32a · Post by **32a** » Thu Apr 20, 2006 11:47 pm

CF Hercs have two GPSs each and dispatched SAR loads don't normally have any weird electronics.

CID · Post by **CID** » Fri Apr 21, 2006 7:06 am

I've encountered similar problems. GPS signals are very weak and can be disrupted by various sources including VHF COMs. Mainly from the COMs on your own airplane, but a high powered external source can do it to.

Furthermore, you never know what "special" mission pacakages they have on military airplanes. GPS jammers are fairly simple devices and its not out of the realm of possibility that a military airplane, even one with a transport role might carry one.

w squared · Post by **w squared** » Fri Apr 21, 2006 7:09 am

Yes, CID. I hear that those black helicopters routinely carry GPS jammer too.

Hedley · Post by **Hedley** » Fri Apr 21, 2006 7:33 am

GPS signals are very weak and can be disrupted by various sources including VHF COMs

Bingo. If you look at the harmonics of 121.15 Mhz and 131.25 Mhz, they stomp all over the very weak L1 1.575 Ghz.

Key the mike, and watch the signal strengths drop on the diagnostic page.

w squared · Post by **w squared** » Fri Apr 21, 2006 9:26 am

Now that sounds far more plausible.

CID · Post by **CID** » Fri Apr 21, 2006 9:55 am

w squared,

The COM interfernce scenario is more likely, but I don't think we can discount any possibility of other devices on a military aircraft. Your statement is nothing but a wind up.

Hedley · Post by **Hedley** » Fri Apr 21, 2006 10:16 am

Heck, I remember reading that some brands of DMEs had oscillators with UHF-ish intermediate frequencies with harmonics that stomped on top of L1.

It doesn't need to be hush-hush, you just need to have bad luck.

I've had civilian airliners taxi by me, and kill my GPS signal strength.

w squared · Post by **w squared** » Fri Apr 21, 2006 10:26 am

CID wrote:w squared,

The COM interfernce scenario is more likely, but I don't think we can discount any possibility of other devices on a military aircraft. Your statement is nothing but a wind up.

Yup. And I'm the only one on these forums that has ever wound anyone up

We all know that you've never done anything of the sort

It's also possible that the C-130 in question was the focal point for all the trans-dimensional energy generated by the alien windmills masquerading as electrical generation devices in the Crownest Pass, but just because something's possible doesn't mean that it's likely enough to merit suggesting it.

Why would a Canadian C-130 have any sort of EW gear aimed at disrupting a GPS reciever? How much sense does that really make?

The fact that we can't 100% discount something doesn't mean that it's plausible.

I'm not interested in getting into a protracted pissing contest over the statistical chances that there was indeed a hypothetical anti-GPS EW device in operation on a CF C-130 on a certain day in a certain location.

Even if such a device were installed on a Canadian C-130, don't you think that they'd be a little more careful about when they turned the bloody thing on? Maybe issue a NOTAM? After all, GA makes heavy use of GPS these days, as do many non-aviation companies. Before a new piece of equipment is put into use in the CF, a doctrine for it's correct use, and the training of personnel in that correct use is developed, tested, and implemented. I would imagine that at some point during that process, somebody somewhere would think "Hey...what about all those civilians that are using GPS?"

I am indeed guilty of attempting to wind you up. But if we all put our egos aside for a minute or three, we'll realize that when someone starts talking out of their arse, it's not such a bad thing to wind them up a wee bit.

Wigwam Willie · Post by **Wigwam Willie** » Fri Apr 21, 2006 1:00 pm

Hey dum dum, use your map for navigation and wear one of these to keep the military out of your head.

Keep dem' chips coming.

heavymetal · Post by **heavymetal** » Fri Apr 21, 2006 1:01 pm

I would have to say that the COM interference sounds about the most plausible. The Herc was ridiculously low and the 15-20 seconds before he passed overehead 200' agl was probably right about the time that he called FSS he was doing another pass.

W Squared is right, IF there was some sort of jamming shit on the aircraft there would have to be Notams etc should the public needed to be informed. I realize that is almost completely unrealistic as none of that stuff should really be public knowledge. What I was wondering was *if* there was such things and existence who is to say somebody wasn't screwing around with it?

By the way Cat - Those gravity surges were out of control today. They were probably responsible for me trying to pick up that fugly at the bar last weekend too.

colourhelp · Post by **colourhelp** » Fri Apr 21, 2006 1:06 pm

[quote="w squared"][quote="CID"]w squared,
the C-130 in question was the focal point for all the trans-dimensional energy generated by the alien windmills masquerading as electrical generation devices in the Crownest Pass[quote="w squared"][quote="CID"]

i've never trusted aliens, but seriously, a tip o' the hat to the aliens for using renewable energy sources while on planet earth. i thank them for leaving our petroleum supplies alone, especially coming up on a busy float season.

CID · Post by **CID** » Fri Apr 21, 2006 2:01 pm

Why would a Canadian C-130 have any sort of EW gear aimed at disrupting a GPS reciever? How much sense does that really make?

You are aware that some missles are guided by GPS sensors I hope.

W Squared is right, IF there was some sort of jamming shit on the aircraft there would have to be Notams etc should the public needed to be informed.

Yes. Just as 208s flying in ice "shouldn't" crash or how an A310 flying across the ocean "shouldn't" have run out of gas.

Mistakes can be made. Perhaps the jammer was activated erroneously due to carelessness or a fault. (That's never happened huh?)

http://www.avweb.com/news/avionics/182754-1.html

w squared · Post by **w squared** » Fri Apr 21, 2006 3:28 pm

CID wrote: You are aware that some missles are guided by GPS sensors I hope.

Yup. And a lot of those JDAMs (because that's what the current GPS guided weapons are called) are aimed at C-130s. A JDAM is a standard low-drag bomb with a set of GPS-steered tail-fins bolted on after the fact. By the time that a JDAM was within a reasonable range of a C-130 mounted GPS jammer, it's ballistic path would already be carrying it onto target. Give me a bloody break, CID. In what universe would a GPS guided weapon be used against a C-130 that's in flight?

I'd also like to ask if you actually READ the article you posted a link to. It talks about accidental interference with GPS signals by various other amplifiers and transponders, and just how easily that can happen.

Why is it so difficult to admit that maybe...just maybe...you were wrong?

It's actually quite liberating. You should try it.

Wigwam Willie · Post by **Wigwam Willie** » Fri Apr 21, 2006 5:55 pm

w squared wrote:
CID wrote: You are aware that some missles are guided by GPS sensors I hope.

Why is it so difficult to admit that maybe...just maybe...you were wrong?

It's actually quite liberating. You should try it.

CRIPPLE FIGHT!!!!

We'd pay money to watch this on the reserve.

Big Pratt · Post by **Big Pratt** » Fri Apr 21, 2006 6:42 pm

CID, when did a 310 run out of gas over the ocean?? I'm only aware of two jet transport overwater "fumes don't burn" incidents.
A hijacked 767 and a 330 with a leak.

Was it a typo or did I miss something in the news?

CID · Post by **CID** » Sat Apr 22, 2006 6:11 am

Why is it so difficult to admit that maybe...just maybe...you were wrong?

I wasn't. My original post should have been enough indication to you that the "jammer" theory was "within the realm of possiblity" meaning that that it was possible, not probable.

You chose to grandstand and "wind-up" the conversation not me. Nothing has changed.

CID, when did a 310 run out of gas over the ocean??

Thanks for the correction Big Pratt. I got the model wrong. You are correct, it was an A330.

WRX · Post by **WRX** » Sun Apr 23, 2006 5:50 pm

Cold Lake had GPS jamming excerise about two months ago.

It was on NOTAM for the whole CYR.