GPS Spoofing effects on 737

[jadrolinija]

Hi everyone,

As GPS Spoofing became a threat in certain regions recently, I would highly appreciate it you could share your experiences and how did it manifest and what can be expected... I am specifically interested about experience on 737 and to see if it has a threat of IRS corruption and if ANP/RNP figures start going up by the start of spoofing... Additionally, did you have a wrong UTC value on aircraft clock too? In summary, what indications or instrument errors can be expected?
Thank you in advance and best regards
J

[IRRenewal]

The IRS is a standalone system that cannot be corrupted by GPS spoofing or jamming (unless of course the GPS position which you used to initialise the IRS was somehow corrupted, but I assume that is not what you are talking about).

If you do have some form of GPS outage your ANP will start going up. In the cruise this is unlikely to be a major issue as you still have IRS and Radio Position available. Not sure why your are asking about RNP. RNP is dictated by what and where you are flying, not by how good your GPS signal is.

I am sure all this is covered in your FCOM and FCTM

[Fursty Ferret]

GPIRS is vulnerable, though, and given that something as new and shiny as a 787 can be confused by the GPS spoofing and decide that it’s 80 miles off track, a 737 is likely to be affected in a similar way.

Even if you ignore the vulnerability in the GPIRS setup, the FMC is also susceptible to spoofing. There’s a reason the Iranians plonked a DME just inside the border that broadcasts on the same frequency as the one over the hedge in Iraq.

I don’t think you can trust the FCOM here - Boeing swear blind that the 787 can’t be position-spoofed when I’ve had to intervene multiple times in Iraqi airspace to stop it turning towards Iran in LNAV.

[IRRenewal]

GPIRS is vulnerable, though, and given that something as new and shiny as a 787 can be confused by the GPS spoofing and decide that it’s 80 miles off track, a 737 is likely to be affected in a similar way.

No, you cannot affect the IRS position in a 737 with spoofed GPS signals once it is initialised correctly. The question wasn't about the 787.

[FlyingStone]

The newer 737s can have IRUs that get continuous updates directly from GPS (MMR).

[jadrolinija]

The IRS is a standalone system that cannot be corrupted by GPS spoofing or jamming (unless of course the GPS position which you used to initialise the IRS was somehow corrupted, but I assume that is not what you are talking about).

If you do have some form of GPS outage your ANP will start going up. In the cruise this is unlikely to be a major issue as you still have IRS and Radio Position available. Not sure why your are asking about RNP. RNP is dictated by what and where you are flying, not by how good your GPS signal is.

I am sure all this is covered in your FCOM and FCTM

Thank you for the information, I am aware what is RNP, I just mentioned it as I wanted to check if ANP values on Legs page (RNP/ANP) go up when GPS spoofing is experienced. I went through the FCOM already but I was also looking for real life experience of Spoofing to get a feedback how exaclty it looked like and what can be expected if flying in affected region.

Fursty Ferret thank you very much for sharing your experience! It exactly what I was wondering if the same symptoms can be expected (Map shift, ANP value increasement, maybe even spurious PULL Up warnings etc.).

If anyone had experienced GPS Spoofing please feel free to share the experience here... Thank you!

[+TSRA]

If anyone had experienced GPS Spoofing please feel free to share the experience here... Thank you!

I've not seen it myself (yet), but I'm told it is happening during day flights on our network in the area of the US/Mexico border on tracks south of Phoenix, AZ, and east across to the TCS VOR. I'm told it's a very specific area that interestingly does not seem to extend into the San Diego area or when crossing into the Gulf east of Corpus Christi as those are both routes I've flown this past week and didn't see anything. I also did not see it a few weeks ago on two red-eye flights down to Costa Rica, but I'm told it happened on the return flight during the day. It's enough to make me wonder if it's an effect of some border operation - or if I'm having my chain pulled by an epic conspiracy.

The way the last guy I flew with described his experience, they noted the ANP slowly started to increase until they received the UNABLE REQD NAV PERF-RNP message on the FMC and the ND. They asked for appropriate traditional navigation clearances from ATC and then actioned the NNC. He said that just as they were getting to step 2, which has you enable radio updating, the ANP slowly started to come back down. They stopped the checklist and within a few minutes the ANP was back below RNP, and the UNABLE REQD NAV PERF-RNP message disappeared. All told he said it lasted about 5 to 10 minutes from when they first noticed the ANP climbing until it returned to within RNP limits.

[Fursty Ferret]

The newer 737s can have IRUs that get continuous updates directly from GPS (MMR).

IRRenewal See above.

[STBYRUD]

Around where I'm flying this is sadly a daily occurrence, and the symptoms depend somewhat on how long you are in an area of GPS interference. It begins usually with a scratchpad message GPS INVALID L / R, and UTC time being removed from the onside clocks. The ANP will increase somewhat of course, depending on the other enabled update sources. In maybe 5 percent of the cases the spoofing was so successful as to actually show an incorrect time and date on the clocks (and therefore also affect the FMS predictions). If this condition persists for a while, you may get a GPS and GLS light (initially on recall if only one sensor has given up). Around this time the RAAS INOP light illuminated and the TERR POS flag will show on the ND instead of the terrain display. I've had false EGPWS warnings twice in such conditions, once on final approach passing 500ft I received a TOO LOW - TERRAIN alert, and another day during rollout after landing a TERRAIN TERRAIN... Lovely stuff, throws you right back to the 90s with conventional navigation.

[jadrolinija]

+TSRA STBYRUD thank you very much for the information, this kind of info is exactly what I was looking for... It helps to collect experience like this just to know what to expect before flying in that region... Thanks a lot!

[ImbracableCrunk]

Happened frequently in Korea approaching the border. GPS-L or -R invalid message and the ANP would increase. Heading away from the border, the GPS would come back and the ANP would go back to normal.

[flypaddy]

In anticipation of spoofing/jamming on a 737NG flight into Cyprus, we disabled GPS position updating. I expected this to lead to some drift but I was surprised at how quickly the ANP increased. In approximately 45 minutes it reached 7. IRS technology should allow aircraft to cross oceans for hours without external position information and remain within 10 so this seems rather feeble.

I had assumed that the ANP value would not be affected by a bad GPS signal if the GPS updating is turned off. Is this incorrect or is something else at play here?

As a footnote, although the FMC had a large positional uncertainty, it was in fact very accurate in its calculated position on this occasion.

[wiggy]

I’m not current anymore but as I recall it ANP is the level the system will guarantee (as I recall it 95% chance of being in the circle), it’s not an objective measure of how accurately the IRS are actually performing.

As you say they usually do much better. I used to cross the pond regularly with triple INS, IRS pre-GPS days and actually being 10 miles out verses a radio fix you got to the far side would be quite unusual.

[jetpig32]

I've not seen it myself (yet), but I'm told it is happening during day flights on our network in the area of the US/Mexico border on tracks south of Phoenix, AZ, and east across to the TCS VOR. I'm told it's a very specific area that interestingly does not seem to extend into the San Diego area or when crossing into the Gulf east of Corpus Christi as those are both routes I've flown this past week and didn't see anything. I also did not see it a few weeks ago on two red-eye flights down to Costa Rica, but I'm told it happened on the return flight during the day. It's enough to make me wonder if it's an effect of some border operation - or if I'm having my chain pulled by an epic conspiracy.

The way the last guy I flew with described his experience, they noted the ANP slowly started to increase until they received the UNABLE REQD NAV PERF-RNP message on the FMC and the ND. They asked for appropriate traditional navigation clearances from ATC and then actioned the NNC. He said that just as they were getting to step 2, which has you enable radio updating, the ANP slowly started to come back down. They stopped the checklist and within a few minutes the ANP was back below RNP, and the UNABLE REQD NAV PERF-RNP message disappeared. All told he said it lasted about 5 to 10 minutes from when they first noticed the ANP climbing until it returned to within RNP limits.

That area is a known hotspot for GPS jamming and spoofing. The military does it frequently out of White Sands/Alamagordo and will be notam'd by ABQ/LAX/ ARTCC. Usually late night. The other known issue is cartels on the border, both used for stealing semis and spoofing CBP drones. I have had multiple jams, but no spoof yet. All but one were NOTAM. Navy will due the same off coast of California from time to time or at China Lake.

[xetroV]

In anticipation of spoofing/jamming on a 737NG flight into Cyprus, we disabled GPS position updating. I expected this to lead to some drift but I was surprised at how quickly the ANP increased. In approximately 45 minutes it reached 7.
Was that with or without DME updating? Just curious, as I would have been similarly surprised with this rapid increase in ANP.

[Speed_Trim_Fail]

Was that with or without DME updating? Just curious, as I would have been similarly surprised with this rapid increase in ANP.

Likewise, as someone who flew the Classic we found thst when DME/DME updating the ANP was (according the FMS anyway) well below 0.3 with no GPS.

[McBruce]

our airline is having continous terrain terrain pull up warnings in spoofing events, 737, Egypt/Cyprus area. We typically inhibit terrain and turn off gps updating until gps signal clears up.

[MechEngr]

Is it time to use phased array receiver antennas to better reject signals from not-satellites?