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.