Airline Pilot Forums

Airline Pilot Forums was designed to be a community where working airline pilots can share ideas and information about the aviation field. In the forum you will find information about major and regional airline carriers, career training, interview and job seeker help, finance, and living the airline pilot lifestyle.




SonicFlyer
03-01-2019, 11:17 PM
https://www.aopa.org/news-and-media/all-news/2019/february/27/more-gps-interference-exercises-planned


PurpleToolBox
04-01-2019, 10:54 PM
https://www.aopa.org/news-and-media/all-news/2019/february/27/more-gps-interference-exercises-planned


I've been GPS jammed. It went on for 18 minutes. Our actual navigation performance grew to a couple of miles (I forget the actual value now). This jamming was not part of an exercise.

rickair7777
04-02-2019, 06:12 AM
I've been GPS jammed. It went on for 18 minutes. Our actual navigation performance grew to a couple of miles (I forget the actual value now). This jamming was not part of an exercise.

Probably not jamming, at least not targeted at you. GPS jamming targeted at you would render it useless. GPS signals are very weak.

It might have been RF inteference, either authorized or unauthorized. Might also have been jamming targeted at something else nearby, depending on where you were when it happened. In the US they issue NOTAMs before they do that.


aviatorhi
04-04-2019, 09:02 PM
Probably not jamming, at least not targeted at you. GPS jamming targeted at you would render it useless. GPS signals are very weak.

It might have been RF inteference, either authorized or unauthorized. Might also have been jamming targeted at something else nearby, depending on where you were when it happened. In the US they issue NOTAMs before they do that.

What he described sounds exactly like GPS jamming where the FMS starts using other means of discerning aircraft position and ANP rapidly rises.

rickair7777
04-05-2019, 07:53 AM
What he described sounds exactly like GPS jamming where the FMS starts using other means of discerning aircraft position and ANP rapidly rises.

The FMS should tell you if GPS is TU. But yes, loss of GPS would result in RNAV via other, less precise means (INS, DME/DME, etc)

aviatorhi
04-06-2019, 07:33 AM
The FMS should tell you if GPS is TU. But yes, loss of GPS would result in RNAV via other, less precise means (INS, DME/DME, etc)

On most Boeings it tells you UNABLE RNP and sometimes it says ATC FAIL. Also your moving map NAV source will change - usually to IRS.

PurpleToolBox
04-12-2019, 04:30 AM
Probably not jamming, at least not targeted at you. GPS jamming targeted at you would render it useless. GPS signals are very weak.

It might have been RF inteference, either authorized or unauthorized. Might also have been jamming targeted at something else nearby, depending on where you were when it happened. In the US they issue NOTAMs before they do that.

What he described sounds exactly like GPS jamming where the FMS starts using other means of discerning aircraft position and ANP rapidly rises.


We were definitely in a area to be jammed. It is an area of known jamming. The company has issues several NOTAMs about it. The problem with our situation was that we were jammed much longer than the company had ever seen before.

The airplane reverted to INERTIAL for navigation, on the POS REF page the GPS position was blank. The RADIO line started tuning DME DME (which it doesn't do unless you lose GPS). We had all sorts of EICAS messages consistent with GPS being lost or jammed (ADS-B OUT L/R, TCAS, TERR POS). The ANP started increasing. I forget the maximum value but it did reach a couple of miles during that short amount of time.

Slowly the GPS signal started to come back and all the messages went away.

It was interesting to watch. Safety reports filed after landing.

galleycafe
04-12-2019, 05:42 AM
I was jammed over southern New Mexico (surprise surprise). Vegas to Lauderdale and GPS never came back. Had to shut the whole plane off for a few minutes in Lauderdale to get it to come back.

Plane Coffee

JohnBurke
04-12-2019, 10:59 AM
What he described sounds exactly like GPS jamming where the FMS starts using other means of discerning aircraft position and ANP rapidly rises.

ANP shouldn't "rapidly rise." If so, then you have bigger problems.

Freight Dawg
04-13-2019, 08:48 AM
The concern over jamming really doesn't apply to us airline guys. We've got plenty of backups. The concern is for the average GA dude. The FAA has been pushing next gen nav, decommissioning VOR's and NDB's and mandating ADS-B. This has pushed most (?) GA guys to use GPS as their primary, or in some cases only, nav. I've personally witnessed probable GPS jamming outside of NOTAMed air space. So if the military is playing nearby is all GA traffic grounded? If a pilot is near the NOTAMed airspace and is accidentally jammed. Is he a primary target only due to his jammed ADS-B transponder? We're going to a single source for nav options. Personally, I feel it's problematic. But who could have seen this coming......

PurpleToolBox
04-17-2019, 11:26 AM
The concern over jamming really doesn't apply to us airline guys. We've got plenty of backups. The concern is for the average GA dude. The FAA has been pushing next gen nav, decommissioning VOR's and NDB's and mandating ADS-B. This has pushed most (?) GA guys to use GPS as their primary, or in some cases only, nav. I've personally witnessed probable GPS jamming outside of NOTAMed air space. So if the military is playing nearby is all GA traffic grounded? If a pilot is near the NOTAMed airspace and is accidentally jammed. Is he a primary target only due to his jammed ADS-B transponder? We're going to a single source for nav options. Personally, I feel it's problematic. But who could have seen this coming......


Sure it is a concern. Backups?

What happens when you lose GPS updating? You revert to inertial and radio updating (I can speak only for 777 and probably most Boeings). Yes, there's still a navigation solution being calculated. However your operations become greatly degraded. You can't fly in RNP4, RNP2, FANS (depending on location), or ADS-B require airspace. You can't fly any procedures that require GPS.

Since writing my first post on the subject above, on my last flight we had GPS jamming indications over Eastern Montana/Western South Dakota. I checked the POS REF page and sure enough we were back to radio updating. It didn't cause any further issues other than some safety paperwork to be filed.

Freight Dawg
04-18-2019, 09:05 AM
Sure it is a concern. Backups?

What happens when you lose GPS updating? You revert to inertial and radio updating (I can speak only for 777 and probably most Boeings). Yes, there's still a navigation solution being calculated. However your operations become greatly degraded. You can't fly in RNP4, RNP2, FANS (depending on location), or ADS-B require airspace. You can't fly any procedures that require GPS.

Since writing my first post on the subject above, on my last flight we had GPS jamming indications over Eastern Montana/Western South Dakota. I checked the POS REF page and sure enough we were back to radio updating. It didn't cause any further issues other than some safety paperwork to be filed.

Please reread my first three sentences. The concern isnít for Boeing guys, itís for light aircraft. Many Cessna, Pipers, etc have very limited backups, if any. Due to the ADS-B mandate, during a GPS outage their position will only be know by primary radar. All transponder, including Mode C, functions will be inoperative.

PurpleToolBox
04-19-2019, 09:52 AM
Please reread my first three sentences. The concern isnít for Boeing guys, itís for light aircraft. Many Cessna, Pipers, etc have very limited backups, if any. Due to the ADS-B mandate, during a GPS outage their position will only be know by primary radar. All transponder, including Mode C, functions will be inoperative.


My point was I don't see it as a concern for just light aircraft.

pangolin
04-19-2019, 09:59 AM
The concern over jamming really doesn't apply to us airline guys. We've got plenty of backups. The concern is for the average GA dude. The FAA has been pushing next gen nav, decommissioning VOR's and NDB's and mandating ADS-B. This has pushed most (?) GA guys to use GPS as their primary, or in some cases only, nav. I've personally witnessed probable GPS jamming outside of NOTAMed air space. So if the military is playing nearby is all GA traffic grounded? If a pilot is near the NOTAMed airspace and is accidentally jammed. Is he a primary target only due to his jammed ADS-B transponder? We're going to a single source for nav options. Personally, I feel it's problematic. But who could have seen this coming......

You are right itís a very important issue considering ADS-B usage for separation.

pangolin
04-19-2019, 10:00 AM
Please reread my first three sentences. The concern isnít for Boeing guys, itís for light aircraft. Many Cessna, Pipers, etc have very limited backups, if any. Due to the ADS-B mandate, during a GPS outage their position will only be know by primary radar. All transponder, including Mode C, functions will be inoperative.

I think you are wrong about mode C being inoperative. When I was in a known jammed area I asked atc if they had our ADS -B and they said no but they still had mode C.

Freight Dawg
04-19-2019, 04:36 PM
My point was I don't see it as a concern for just light aircraft.

My apologies. I misread your post.

Cheers

rickair7777
04-19-2019, 06:01 PM
I think you are wrong about mode C being inoperative. When I was in a known jammed area I asked atc if they had our ADS -B and they said no but they still had mode C.

Depends on the spectrum(s) involved, and the power at your location.

GPS signals are pretty weak, I don't know for sure but strongly suspect that mode C (and other modes) will take more power to jam than GPS. GPS is probably always going to be the weak link in terms of which systems are susceptible to jamming or other interference. That and sat based wifi :rolleyes:

JamesNoBrakes
04-19-2019, 09:12 PM
Please reread my first three sentences. The concern isnít for Boeing guys, itís for light aircraft. Many Cessna, Pipers, etc have very limited backups, if any. Due to the ADS-B mandate, during a GPS outage their position will only be know by primary radar. All transponder, including Mode C, functions will be inoperative.

After 2020, no reason for people to keep mode c transponders in their planes, I assume many will be removed, those that remain probably won't be serviced or ever turned on.

PerfInit
04-20-2019, 05:13 AM
The ďbackupĒ plan is still ground-based navigation, VORís. With NextGen implementation, there is a Minimum Operational Network (VOR MON) that will be maintained. For FMS that revert to DME/DME/IRU updating with the loss of GPS, there will also be aMinimum number of DME stations

rickair7777
04-20-2019, 06:29 AM
The ďbackupĒ plan is still ground-based navigation, VORís. With NextGen implementation, there is a Minimum Operational Network (VOR MON) that will be maintained. For FMS that revert to DME/DME/IRU updating with the loss of GPS, there will also be aMinimum number of DME stations

Yes. They have to maintain a ground-based backup. Every single GPS satellite flies over every single one of our potential antagonists, several of which have asat capability. If so inclined, they could probably splash the entire constellation in a few days.

Singlecoil
04-21-2019, 07:38 AM
If your ANP rapidly rises, the IRUís might have been initialized with a bad position. I donít know about the other Boeings, but on the 737 it displays a ďlast positionĒ. Some pilots were using that to initialize the ADIRUs (and some instructors were teaching that). The problem with doing it that way is the last position shown isnít where you are at the gate, itís where the airplane transitioned to ground mode on the previous flight. If I had to guess, I would say it is where the jet slowed to about 80 knots or so on the previous landing. You can pull out the 10-9 and use the lat/long tick marks in the margin to see it for yourself. For most airports it isnít a big deal, but in LAS or ORD you have just told the IRUís that they are over a mile from where they actually are. Now you lose GPS and suddenly you have an ANP problem. Use GPS position to initialize the IRUís or if that isnít working, use the gate coordinates.

Blackhawk
04-26-2019, 07:34 AM
I had one years ago where the variation would be shifted dramatically. Say from E3 to W30. Your location would be accurate over CPs and destination, but not enroute. Because of this, we would not get a GPS caution as it didn't know there was a problem. Took us a few flights to figure out what was going on.

iPilot
04-26-2019, 03:03 PM
If your ANP rapidly rises, the IRUís might have been initialized with a bad position. I donít know about the other Boeings, but on the 737 it displays a ďlast positionĒ. Some pilots were using that to initialize the ADIRUs (and some instructors were teaching that). The problem with doing it that way is the last position shown isnít where you are at the gate, itís where the airplane transitioned to ground mode on the previous flight. If I had to guess, I would say it is where the jet slowed to about 80 knots or so on the previous landing. You can pull out the 10-9 and use the lat/long tick marks in the margin to see it for yourself. For most airports it isnít a big deal, but in LAS or ORD you have just told the IRUís that they are over a mile from where they actually are. Now you lose GPS and suddenly you have an ANP problem. Use GPS position to initialize the IRUís or if that isnít working, use the gate coordinates.

I believe the FMS automatically updates the IRS with the runway position when you hit the TOGA button on a Boeing. Only concern with putting in exact coordinates for alignment is if your thrust management computer or auto throttles are inop. Otherwise last position or just the airport coordinates works just fine.

Swedish Blender
04-27-2019, 09:50 PM
Only time my GPS has been jammed was at the corner of Iraq, Iran, and Turkey.

Is that a problem?

;)

pangolin
04-28-2019, 01:38 AM
Only time my GPS has been jammed was at the corner of Iraq, Iran, and Turkey.

Is that a problem?

;)

Itís happening in the US frequently.

JohnBurke
04-28-2019, 03:29 AM
If your ANP rapidly rises, the IRUís might have been initialized with a bad position. I donít know about the other Boeings, but on the 737 it displays a ďlast positionĒ. Some pilots were using that to initialize the ADIRUs (and some instructors were teaching that). The problem with doing it that way is the last position shown isnít where you are at the gate, itís where the airplane transitioned to ground mode on the previous flight. If I had to guess, I would say it is where the jet slowed to about 80 knots or so on the previous landing. You can pull out the 10-9 and use the lat/long tick marks in the margin to see it for yourself. For most airports it isnít a big deal, but in LAS or ORD you have just told the IRUís that they are over a mile from where they actually are. Now you lose GPS and suddenly you have an ANP problem. Use GPS position to initialize the IRUís or if that isnít working, use the gate coordinates.

There is absolutely no justification for initializing the IRU without verifying current position. Doing otherwise is poor airmanship.

One should verify what the former residual IRU performance was, if available, before bringing the system up, however, to get an idea of which unit might be the most efficient in the event of a fail down and a need to rely on one without other nav input. Again, just good airmanship to now which unit shows the strongest and most accurate, before starting the flight. I very seldom see anybody do this.

It's a bit like not verifying the fuel upload. I see most look at the fuel indication and if it matches what's wanted, the crew is happy. It seems to be a lost basic that one should look at the previous ending fuel, fuel upload, add them and note any discrepancy that isn't explained by APU burn, etc. Simply things, but important, and should be done every time.

As for jamming issues: while there may come a time when ground based navaids or gone, that time is not today. I've never been an advocate of an all-eggs-in-one-basket approach, and am not today. There are locations, of course, that rely only on RNAV and GPS for approaches, arrivals, departures, etc, but when operating IFR to such locations, good airmanship dictates having options that do use ground based navaids, including alternates in mind. It's been mentioned that these concerns are chiefly for general aviation aircraft. Again, good airmanship dictates having a plan B.

It's possible to paint one's self into a box. Don't do that.

I also fly general aviation, sometimes in aircraft with no nav systems; it's either charts or a handheld GPS (and charts); with loss of GPS, then it's pilotage and dead reckoning.

The latter two still work. If one insists on going IFR, and has only RNAV capability, then we're back to good airmanship, which means having a plan to get to VMC and to fly visually.

Singlecoil
04-28-2019, 10:02 AM
I believe the FMS automatically updates the IRS with the runway position when you hit the TOGA button on a Boeing. Only concern with putting in exact coordinates for alignment is if your thrust management computer or auto throttles are inop. Otherwise last position or just the airport coordinates works just fine.

This is a good discussion. Actually, the TOGA button update only works with when the GPS updating is selected off, which is not common. But the important distinction is that it only updates FMC position, not the IRU position. The only time the IRU's receive a position is when they are in align mode. A lot of people think the GPS's are constantly updating the IRU, but that is not the case. It is critical to put your actual position, either from a GPS sensor or from using the gate coordinates, when you are aligning the IRU's. You can hit the POS button on the NAV display and it will show you where the IRU's think they are. Most of the time, the FMC will ignore the IRU position and use GPS position, but if you are in an area where the GPS's are jammed and there aren't many navaids around (think northwest of Vegas) then the FMC will revert to using IRU position. Hopefully it was aligned correctly and not given a position miles away from where the alignment took place.

aviatorhi
04-28-2019, 12:00 PM
ANP shouldn't "rapidly rise." If so, then you have bigger problems.

Clearly this has never happened to you... while it happens about once every month or two to me.

Rapidly is subjective, but in the span of a few minutes you'll be at a few miles when on inertial only.

rickair7777
04-29-2019, 09:27 AM
Clearly this has never happened to you... while it happens about once every month or two to me.

Rapidly is subjective, but in the span of a few minutes you'll be at a few miles when on inertial only.

It might raise relatively rapidly immediately following GPS loss, but it should quickly settle down at a reasonable (for non-GPS RNAV) value.

If you're oceanic, on INS only, then ANP should very gradually increase over time without GPS. Same for a hypothetical total jamming of all sat and ground based nav over land.

Most of the airplanes we fly used to do RNAV all day long without GPS, and many of them did oceanic with INS only a few decades ago. It shouldn't all just go to poop if you lose GPS.

JohnBurke
04-29-2019, 12:11 PM
Clearly this has never happened to you... while it happens about once every month or two to me.

Rapidly is subjective, but in the span of a few minutes you'll be at a few miles when on inertial only.

Fly better equipment, or learn to properly initialize before you leave the gate.

captjns
04-30-2019, 04:29 AM
Clearly this has never happened to you... while it happens about once every month or two to me.

Rapidly is subjective, but in the span of a few minutes you'll be at a few miles when on inertial only.

GPS jamming NOTAMS, alerts issued by the FAA. GPS anomaly? Yeah consistently near an intersection over the Italian/Swiss boarder. Got they typical RNP message in the FMC/CDU. Came back to life before I had the chance to cancel the message.

Operated across the Pacific with IRSís. Average leg was 10 hours plus. Required to log velocities and distance errors 10 minutes after the parking brake was set. Trying to remember the greatest distance error was about 2 miles. That said No biggy, unless you need to accomplish a LPV approach.

BobZ
04-30-2019, 08:18 AM
Excess iru drift is still tabulated i believe.

PurpleToolBox
05-03-2019, 04:17 PM
Operated across the Pacific with IRSís. Average leg was 10 hours plus. Required to log velocities and distance errors 10 minutes after the parking brake was set. Trying to remember the greatest distance error was about 2 miles. That said No biggy, unless you need to accomplish a LPV approach.


And now we have tighter airspace and stricter required navigational performance requirements. :rolleyes:

aviatorhi
06-14-2019, 05:09 PM
Fly better equipment, or learn to properly initialize before you leave the gate.


Good idea.... but since I already do that do you mind telling the Syrians and Russians to stop jamming the GPS on the Turkey/Iraq border as well? Smartass.


It might raise relatively rapidly immediately following GPS loss, but it should quickly settle down at a reasonable (for non-GPS RNAV) value.

If you're oceanic, on INS only, then ANP should very gradually increase over time without GPS. Same for a hypothetical total jamming of all sat and ground based nav over land.

Look, these are relative concepts... what is rapidly to me might not be the same to you. Typically in a remote area (without ground based NAV) it rapidly gets to about 3-4 NM and then the rate slows down tremendously.

Most of the airplanes we fly used to do RNAV all day long without GPS, and many of them did oceanic with INS only a few decades ago. It shouldn't all just go to poop if you lose GPS.

Yeah, but this isn't 1998, some of the ways ANP is being calculated and implemented (as well as the software) have changed since then. I sure how you wouldn't consider ANP values in the 3-4 range as acceptable for any kind of RNAV based approach in 2019.

JohnBurke
06-15-2019, 02:09 AM
Smartass.


Ah, an intellectual.

Good idea.... but since I already do that do you mind telling the Syrians and Russians to stop jamming the GPS on the Turkey/Iraq border as well?


You tell them. It's a combat zone. Go figure.

If you're already flying better equipment, then it's not really an issue, is it?

ShyGuy
06-15-2019, 10:20 AM
It's a bit like not verifying the fuel upload. I see most look at the fuel indication and if it matches what's wanted, the crew is happy. It seems to be a lost basic that one should look at the previous ending fuel, fuel upload, add them and note any discrepancy that isn't explained by APU burn, etc. Simply things, but important, and should be done every time.

Assuming one has an ability to do that. When I walk on the plane and it's already fueling, I have no way to know what the previous flight's remaining fuel was. If I get on the plane and it hasn't fueled yet, I can see the current FOB is the previous flight arrival fuel. However, after my fueling is done I don't know how many gallons are added. The electronic fuel slip delivered on ACARS only shows the paperwork required FOB.

Before the merger, our own airline delivered fuel slips that showed previous arrival fuel and gallons added and I would do that math just like you said to verify it. It was actually part of the our procedures. Not anymore. I don't see how that can be done now, we just don't get that info anymore. SOPs call to 'only' verify the FOB on the screen.



As for jamming issues: while there may come a time when ground based navaids or gone, that time is not today. I've never been an advocate of an all-eggs-in-one-basket approach, and am not today. There are locations, of course, that rely only on RNAV and GPS for approaches, arrivals, departures, etc, but when operating IFR to such locations, good airmanship dictates having options that do use ground based navaids, including alternates in mind. It's been mentioned that these concerns are chiefly for general aviation aircraft. Again, good airmanship dictates having a plan B.

It's possible to paint one's self into a box. Don't do that.

I also fly general aviation, sometimes in aircraft with no nav systems; it's either charts or a handheld GPS (and charts); with loss of GPS, then it's pilotage and dead reckoning.

The latter two still work. If one insists on going IFR, and has only RNAV capability, then we're back to good airmanship, which means having a plan to get to VMC and to fly visually.

Well stated :)

727C47
06-16-2019, 03:01 AM
There is absolutely no justification for initializing the IRU without verifying current position. Doing otherwise is poor airmanship.

One should verify what the former residual IRU performance was, if available, before bringing the system up, however, to get an idea of which unit might be the most efficient in the event of a fail down and a need to rely on one without other nav input. Again, just good airmanship to now which unit shows the strongest and most accurate, before starting the flight. I very seldom see anybody do this.

It's a bit like not verifying the fuel upload. I see most look at the fuel indication and if it matches what's wanted, the crew is happy. It seems to be a lost basic that one should look at the previous ending fuel, fuel upload, add them and note any discrepancy that isn't explained by APU burn, etc. Simply things, but important, and should be done every time.

As for jamming issues: while there may come a time when ground based navaids or gone, that time is not today. I've never been an advocate of an all-eggs-in-one-basket approach, and am not today. There are locations, of course, that rely only on RNAV and GPS for approaches, arrivals, departures, etc, but when operating IFR to such locations, good airmanship dictates having options that do use ground based navaids, including alternates in mind. It's been mentioned that these concerns are chiefly for general aviation aircraft. Again, good airmanship dictates having a plan B.

It's possible to paint one's self into a box. Don't do that.

I also fly general aviation, sometimes in aircraft with no nav systems; it's either charts or a handheld GPS (and charts); with loss of GPS, then it's pilotage and dead reckoning.

The latter two still work. If one insists on going IFR, and has only RNAV capability, then we're back to good airmanship, which means having a plan to get to VMC and to fly visually.

John, God bless that, I used to fly a Champ with just a whiskey compass and a sectional, GPS was cheating, good on you