GPS Jamming Report, Korea
 

Read an article in the news that concerns me. This is a non trivial safety issue that probably isn't confined to North Korea.

World News - N. Korea accused of jamming commercial flight signals

If the GPS signal is being jammed while you are in the terminal area, what does it look like in the cockpit when the signal begins to go wrong.

Do you get caution lights or warnings or ECAMS notifications?

More importantly, how often does this happen and you, as flight deck crew, are not aware?

I suspect that by the time you are on the ILS, a GPS jam probably would not materially influence your approach, but what about if you have to do a missed approach? If GPS is being jammed, how will you know?

Have any of you experienced this?

As I am not sure what the NORKERS are jamming, nor how, perhaps all that happens is that one of the signals feeding your system goes unreliable, but there are enough signals from the constellation to allow the system to remain effective.

The UK has been running GPS jamming trials north of London for a year or so now. There's been a NOTAM on and off warning crew to disregard GPS in the area (which includes Stansted Airport).

You're kidding, right? :rolleyes:

Yep flying into Stornoway in Scotland they have an exercise every year were the GPS is jammed on and off for two weeks.

To be honest it can happen anywhere in the UK. The was a little scrot in the Isle of White that had a jammer for about 3 months or it could have been the navy range areas.

Experienced a similar GPS jamming out of Calicut and Jeddah recently. Nothing on the Notam though. ATC didnt have a clue either.

[SLF]: what ever happened to inertial nav (INS)? There was a time when that was the miracle that got airliners across oceans within a km or so of intended.

It's still there, it drives many of the flying instruments as well as providing back-up to GPS.

We have the problem on a regular basis operating around Syria (officially no jamming takes place but still the faithful GNSS goes kaput more often than not around there)... The 737NG gives a scratchpad message, (GPS L/R INVALID) and will stop updating from there. ANP will go up obviously. On most of our planes the DME-DME updating is off by default, worth checking if you are planning to stay in the area for longer ;)

what exactly is the purpose of doing this?:ugh:

If you thought someone was likely to shoot GPS guided cruise missiles at you, I think you would soon work it out, Irish :rolleyes:

Checkerboard: Yeah, I kind of realized that. My thought was that if steam-powered 1980's INS could get one through some 8 hours of flight with a km of accuracy, by 2011 better solid-state gyros and hugely better computers could, if desired, know the state of the platform with sub-meter and fractional-degree accuracy and thus internally* provide for all the navigation one would need up to Cat III landings. (*perhaps granted an external fix now and then to take care of any long-term drift that the platform might still be guilty of.)

As an extreme example it was noted during AF447 discussions that the inertial stuff knew the a/c was seriously pitched up, but wasn't designed to mention it to the humans. (If I understood that correctly.)

Countering my suggestion is the presumed fact that the military continues to use GPS for delivering ordnance to target. But that might mean that GPS is "good enough" and cheaper - a factor for their single-use toys, or that I don't know what they're actually using, or just that no one has given Lockheed or Boeing some money to look into the alternative, or that GPS is the sexy Thing du Jour.

STBYRUD - you said Why is that?? I don't have a lot of experience of state-of-the-art navigation, but on the only type I have flown with FMS updated by GPS, DME/DME, and laser inertial, the manual definitely said that DME/DME is the most accurate - makes sense that it would be more accurate than GPS as it is basically the same method of determining position, but from fixed position beacons rather than ones flying round in space..........

Thanks for the responses.

I guess most modern airliners have inertial nav ... so my Terminal Area question is covered by another system.

The question initially came to me as something like "do the children of the magenta line" have a back up plan if the GPS goes whack, but that wasn't a very good question, it turns out.

DME/DME is more accurate than GPS, really? That's a bit of a surprise, what type and brand of FMS manual stated that? I'll admit it has been five years since I have retired, but it was my understanding that the GPS was the most accurate navigation system one could have.

Have things changed that much?

INS/GPS
 

Any little chav can buy a GPS jammer, there small enough now to be concealed in a fag packet and be able to block GPS receivers for approx 5kms. I'm no expert on the nav systems of modern airliners but i'll hazard a guess that they work the same as most INS/GPS systems?
If so then when the INS initialises to it'd start state, when ever the laser gyros detect movement in the linear, and vertical plane it is able to provide a direction and distance travelled by the movement of the gyros. The GPS system just aids in the correction of any errors in the INS. This is a very basic principle behind any INS/GPS system, even down to precision guided weapons. The faster something travels the more inherent GPS lag is, so the missile has moved past and beyond where the GPS has just said where the missile has been, with out the INS system the phrase a dog chasing it's own tail springs to mind.

FMC and GPS position always seem to coincide the times I have checked. The navaid updating is usually pretty accurate as well but not to the same degree as the GPS and depends on navaid coverage. The IRS is the least accurate and after a few hours could be a couple of miles off. Sometimes they even come and go, had one IRS that had been reported dodgy drift something like 3 miles off in 30 min to eventually end up within a mile or so of the aircraft position at the end of the day… randomly of course.

Obviously a GPS update is more accurate than DME updating, the story I have been told is that when DME updating is on together with GPS it only degrades the actual navigational performance by introducing another source with a certain uncertainty... The problem is that in said area the authorities are planning to roll out RNP-GNSS approaches :D

One HARM would do the job nicely...

There are different guidance systems depending on the job and the threat environment. Laser, INS, GPS, GPS/INS systems, electro-optical, CCD, IIR, etc.

You don't think the military would put all eggs in one basket, now would you?

poorjohn,

Wasn't designed to mention it... apart from the big artificial horizon display in front of each pilot you mean? :rolleyes:

I think he meant the AoA.

Once happened to me in Djbuti, Africa, nov 2009.

It was jammed all right. No signal recepcion at all in the plane until getting airborne and away from the airfield.

Terrible situation andit was my first.

All the best,

Sydy

I experienced it many times taking off on Gimpo 32L/R. You'd get one GPS INVALID message and then a minute later, the other one would go. Once you were far enough south of the border, they would come back.

Everyone knew it was happening. Or all the locals, anyway.

Thanks! :ok:

As long as you know that theres no GPS signal, it is not a big deal.

Problem would be if the signal is still there, but giving wrong position

Con-pilot -

The equipment was a Universal UNS-1A, with inputs from laser inertial gyro, GPS, and multi scanning DME/DME/DME. To quote from the manual

The manual makes it clear that the multiple DME position solution is considered the most accurate, when receiving sufficient DME signals. It seems to make sense to me, as DME and GPS are both calculating position by timing the radio signal, but with GPS, both transmitter and receiver are moving in space, whereas with DME one half of the equipment is in a fixed accurately known position

Pretty funny...first off, no one here is going to know if they are being jammed...as jamming can encompass a variety of tactics. Always a laugh when I come here.

In that case it must be a bizzare coincidence that last night 20 miles south of Incheon, "GPS INVALID" pops up in the CAS window. I have never had this anywhere else.

A few seconds later we got the subsequent CAS message;

"GPS INTEGRITY PRESERVED" ;)

The body of knowledge about GPS jamming is growing quite a bit thanks to the uptick in countries that see themselves as badasses:

1) Jamming is most often directed at the L1 signal, but L2 is sometimes hit as well.

2) Jammers (personal privacy devices and high power military transmitters) use strong "RF chirps" that sweep the whole band and cover up any weak GNSS signals.

3) Actually spoofing a GNSS signal to cause a gross navigation error is difficult, but not impossible, and must be directed at a specific victim. Very expensive - but motivated governments would do it for a valuable target.

4) Aircraft will experience an increase in ANP and have to fall back on DME-DME as the next most accurate navigation method.

Here's a good place to troll for technical info on the subject:
Massive GPS Jamming Attack by North Korea | GPS World

and

GPS World - April 2012

Look to the Russians and Chinese if you want to buy this technology. Cheap devices can cost a hundred USD; high power jammers may run several thousand USD and up.

In US recently military jaming trials
 

About a month or so ago over the mid west US, the military were trialing jaming of gps.

Bloody annoying for a while as the signal went on and off and the associated warnings came and went.

A DME signal has an accuracy that is rated at 3% of distance, with a maximum predictable accuracy of 90 meters. When you have multiple signals, the software can balance them. As the ac is moving, each DME source is being updated. Update rates and distance affect each accuracy level, so that is why multiple are better than one.
The accuracy is also based on the DME itself, as the RNAV system balances the ranges, it has to take into account multi-path errors, looking at signal in space accuracy tolerances along the procedure path. The ANSP is supposed to continuously validate the signals, but that requires a flight validation, so well, there you are, put up a new building and all bets are off. Even then, the ICAO standards are to maintain accuracy at 95%.
In designing procedures, I frequently have to do a DME coverage analysis, which will fry brain cells for sure...
http://operationsbasednavigation.com...E-coverage.jpg
Along with multi-path errors, the RNAV system will identify errors resulting from field strength below min standards.
All of this is why DME/DME accuracy is at best around 90 meters.

Now about that GPS....
in regards to jammers, the hand held units only have very limited ranges, and in reality, are only used to either block the GPS signal from your phone, or the vehicles GPS. There used to be higher powered units, that would be used around public and secure building, that had ranges of up to 300m, but those had significant power requirements.
There are units used by the military, but have very significant power and signal requirements.

What I believe most of you are experiencing, especially with the the messages such GPS L/R INVALID, GPS INTEGRITY PRESERVED, are the result of the HAL of your unit, passing the HAL. Given some of the locations that were talked about, as referencing the RAIM map below, one can also surmise the reason for some of the error messages.
I guess I would have to ask about the process for determining the RAIM prediction for your company as well, and how that information gets to each flight deck. I know that many Operational SOP's require the RAIM prediction along the flightpath, and this will determine if the flight may use RNP, or specifically, which RNP levels can be used.
From the RAIM prediction map, one can always see issues along the equatorial regions in general, but site specific and route prediction is required.

While this was posted on another thread, it is applicable here as well. What I suspect is either you are not looking at the RAIM predictions, and/or dont understand what they mean. In the text when I speak of the Alarm, that is that the unit is returning messages such as GPS INVALID, and can also show certain RNP levels not available.

RAIM is built into the GPS system on the aircraft, and is part of what is balancing all the the different sat connections and detecting faults the pseudorange measurements.
(in regards to Gimpo, this is a GBAS test setup, but GBAS only broadcasts the corrected algorithm, so I have not heard of a GBAS confusing a non GBAS system, and the Airspace around Korea is a difficult one anyways)

When you look at RAIM predictions,they are configured with 3 modes, Fault Detection, FD(5 sats req'd), Fault detection and exclusion, FDE (6 sats req'd), and if Selective Avail, SA is turned on.

For 3D navigation, you need a min of 4 sats, but will have no RAIM fault detection.

The RAIM function that you will see in the box is represented with the HIL number. Depending on your box, and RNP level set, the box will alarm when the HIL number reaches a certain threshold, the HAL, telling you that you horizontal integrity is getting near the limit Horizontal Alarm Limit of the RNP level.
The HIL, HAL, and HPL numbers are some voodo combination of the secret sauce inside each box, and given the potential combinations of algorithms and factors, I have no idea how alarm limits are decided.

As an example, during flight validation testing, with the Smiths box, RNP level 0.3, I had the box alarm at HIL of .51 in a 737, while in a 320,with a Honeywell box on RNP 0.1 it alarmed at .67....

Hope that helps! GPS/WAAS RAIM prediction tools

Depending on the model, variant of the FMS, different things can happen. On the MCDU PROG page, you can see the predictive GPS req'd, estimated, and accur values. Looking at this page can give an explanation of the "PRIMARY LOST" or "GPS UNAVAIL".

The different boxes have different features with a hybridized HIL that estimates when GPS integrity falls below certain limits, creating an 'equivalent' HIL, but for short amounts of time, which differs depending on equipment. Usually the time of the hybrid HIL is linked to the IRU, but most are in the 6 to 7 minute range where the FMS will estimate the time to reach HAL, and therefore the error messages.