GPS Interference Testing Affecting Biz Jets??????

ARFlyer

ARFlyer

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http://www.avweb.com/avwebflash/news/GPS-Interference-NOTAM-For-Southwest-226365-1.html

AvWeb says this months GPS Testing NOTAM states that Embraer Phenom 300 should completely avoid most of the west coast. FAA is saying the testing can affect the flight control systems of the jet.

What kinda of testing affects aircraft systems beyond the GPS units? Are the GPS systems that important to their basic flight control systems?

Actual NOTAM: https://www.faasafety.gov/files/notices/2016/Jun/CHLK_16-08_GPS_Flight_Advisory.pdf
 
I would imagine that maybe the Phenom 300 avionics rely heavily on the GPS signal to where it won't revert to a non-GPS source when loss of GPS signal occurs when in "GPS" mode for navigation. Other aircraft types use an alternate logic when dealing with loss of GPS signal which doesn't cause flight control dangers.
 
The flight controls are intigrated into the GPS and AHRS system. No GPS, the -300 looks like 6PC trying to fly a non-cirrus; utter confusion ensues and the NTSB is on stand by when he takes off. A 9m jet that can't fly without GPS.
 
There's got to be more to this story about the Phenom 300. But I haven't found anything except reports of this notam.
 
I bet that all new AHRS systems rely on GPS. I don't think a single modern jet has a INS system of yesteryear. So, I expect this could happen to any modern jet. It's just that it happened to fail the GPS 1 and 2 in this particular Phenom, hence the Notam. With failed GPS'es in other modern planes, it might be the same.
 
So, if GPS is lost (say via a $20 GPS jammer from China) what happens? Is the plane uncontrollable?

So they realize how huge a security/safety problem this is? I can't imagine something like this getting through certification.
 
ARFlyer said:
Well that is just kinda dumb. You'd think they design the system to work without GPS. I wonder if they will have to release a fix or just roll with it.
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I see what you did there. :p

But, yeah, this is crazy.
 
dans2992 said:
So, if GPS is lost (say via a $20 GPS jammer from China) what happens? Is the plane uncontrollable?

So they realize how huge a security/safety problem this is? I can't imagine something like this getting through certification.
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So basically someone with basic GPS jammer that one could easily buy or, with limited skill, build would cripple this jet. Seriously WTF.
 
stratobee said:
I bet that all new AHRS systems rely on GPS. I don't think a single modern jet has a INS system of yesteryear. So, I expect this could happen to any modern jet. It's just that it happened to fail the GPS 1 and 2 in this particular Phenom, hence the Notam. With failed GPS'es in other modern planes, it might be the same.
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Nope. I don't think this common at all. Never heard of it until now. You can figure nothing in 121 service would be this way. If it is common I would be very surprised.
 
stratobee said:
I bet that all new AHRS systems rely on GPS. I don't think a single modern jet has a INS system of yesteryear. So, I expect this could happen to any modern jet.
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I'll take that bet. While they might not have what you think of as an inertial navigation system (INS), most 'modern jets' have inertial *measurement* units, or IMUs. Many/Most may use GPS for filtering or solution refinement or use the IMU for refinement of the GPS solution but I doubt you'll find many airplanes that lose stability augmentation and envelope protection without GPS.

Nauga,
self-contained
 
Yep, a very poor design if GPS signal is made to be crucial to AHRS processing. I have designed my own systems (as Apps) and see no reason to couple GPS and AHRS too tightly (though fine as long term cross-check). Also, I see no reason to exclude input from GLONASS and possibly others, since all modern GNSS sensor chips seem to provide support for them.
Still not sure how GPS outages or interference tests affect GLONASS and friends, but it certainly can't hurt to have a completely independent input, esp. when it's available for (nearly) free.
 
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NoHeat said:
Wow!

Does the Phenom 300 fleet use Garmin 1000 and Garmin 3000?

I wonder if Garmin 1000 can have this problem on other planes.
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No. G1000 is not affected by GPS interference unless you are navigating by GPS. It will keep the blue side up just fine. It may show you in the wrong place and come up with some "interesting" flight stats. But the PFD is unaffected except for the CDI.

Having said that, and LPV approach in the clouds wouldn't be much fun, particularly if the interference were intermittent.
 
RotorDude said:
Yep, a very poor design if GPS signal is made to be crucial to AHRS processing. I have designed my own systems (as Apps) and see no reason to couple GPS and AHRS too tightly (though fine as long term cross-check). Also, I see no reason to exclude input from GLONASS and possibly others, since all modern GNSS sensor chips seem to provide support for them.
Still not sure how GPS outages or interference tests affect GLONASS and friends, but it certainly can't hurt to have a completely independent input, esp. when it's available for (nearly) free.
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I had an incident once where the Garmin GPS antenna started de-laminating internally and jammed all GPS receivers onboard. (There was a flaw in this model of antenna - it's somewhat common).

Anyhow, my devices that supported GLONASS still worked, for example a newer (at the time) iPhone. It was interesting.
 
dans2992 said:
I had an incident once where the Garmin GPS antenna started de-laminating internally and jammed all GPS receivers onboard. (There was a flaw in this model of antenna - it's somewhat common).

Anyhow, my devices that supported GLONASS still worked, for example a newer (at the time) iPhone. It was interesting.
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If you had GPS on your iPhone, I assume it wasn't connected to the certified GPS antenna, in which case it should have been able to use normal (non-GLONASS) GPS too. Or am I missing something?
 
RotorDude said:
If you had GPS on your iPhone, I assume it wasn't connected to the certified GPS antenna, in which case it should have been able to use normal (non-GLONASS) GPS too. Or am I missing something?
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The antenna de-lamination somehow caused a signal to be emitted that actively jammed other GPS signals onboard. Even those not fed from that antenna! Yeah, it was bad. Others have experienced the same issue.

Took us weeks to isolate the problem. At first I thought it had to do with that "GPS interference testing" they're always doing.
 
stratobee said:
I bet that all new AHRS systems rely on GPS. I don't think a single modern jet has a INS system of yesteryear. So, I expect this could happen to any modern jet. It's just that it happened to fail the GPS 1 and 2 in this particular Phenom, hence the Notam. With failed GPS'es in other modern planes, it might be the same.
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We have 3 IRSs in our plane. I'd wager it's one of the most advanced biz jet there is. The 1AHRS is only used used for the standby AI.
 
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FORANE said:
There are EFIS manufacturers in the experimental world whose AHARS function independently of GPS. One example is the GRT:
http://www.grtavionics.com/commercialahrs.html
http://www.grtavionics.com/adaptiveahrs.html
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GRT only works without GPS if optional external magnetometer is used to unload the AHARS. Otherwise, GRT depends on GPS just like all other EFIS except Sandia's (which uses software-defined emulated friction to find the vertical). Here's the relevant quote from GRT documentation:

"WARNING: The attitude indication of the Mini-B is dependent upon reception of a reliable GPS signal at all times. // If GPS track information is lost and the Mini is not equipped with the remote magnetometer, the screen will show valid attitude data for 100 seconds with a count-down timer showing the time remaining."

The reason why all EFIS must either use an external signal or drift is known as "Pendulum Fallacy".
 
zaitcev said:
The reason why all EFIS must either use an external signal or drift is known as "Pendulum Fallacy".
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When I analyzed sources of error in FOGs, I found five different terms that contributed to drift. None of them were related to Goddard's rocket. They were things like discreteness/sampling noise, rate noise, and so on. Because all solid state gyros are rate gyros, any source of noise will cause drift analogous to a random walk.
 
zaitcev said:
GRT only works without GPS if optional external magnetometer is used to unload the AHARS. Otherwise, GRT depends on GPS just like all other EFIS except Sandia's (which uses software-defined emulated friction to find the vertical). Here's the relevant quote from GRT documentation:

"WARNING: The attitude indication of the Mini-B is dependent upon reception of a reliable GPS signal at all times. // If GPS track information is lost and the Mini is not equipped with the remote magnetometer, the screen will show valid attitude data for 100 seconds with a count-down timer showing the time remaining."

The reason why all EFIS must either use an external signal or drift is known as "Pendulum Fallacy".
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The GRT Mini uses a different AHARS and is designed for VFR only. The adaptive AHARS has an internal magnetometer and is capable of functioning without GPS or the external magnetometer.
 
MAKG1 said:
When I analyzed sources of error in FOGs, I found five different terms that contributed to drift. None of them were related to Goddard's rocket. They were things like discreteness/sampling noise, rate noise, and so on. Because all solid state gyros are rate gyros, any source of noise will cause drift analogous to a random walk.
Click to expand...

You're thinking about a different problem. Suppose that an airplane was flying straight for 1110 km, then turned 90 degrees left. If AHARS weren't constantly correcting for vertical, the EFIS would then show a 10 degree bank.
 
So, is this an actual problem? Can those airplanes actually crash with no GPS? Or is it an "abundance of caution" thing.
 
zaitcev said:
Suppose that an airplane was flying straight for 1110 km, then turned 90 degrees left. If AHARS weren't constantly correcting for vertical, the EFIS would then show a 10 degree bank.
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You've already said that a GPS is not required for Schuler tuning...so what's the issue? Military IMUs, INSs, and IRUs or whatever (S)AHARS are not solely dependent on GPS for correction - are non-experimental Commercial AHARS (besides those in the EMB-300)? With no alternate means of correction? How is it that my Dynon D-10A has no GPS input but still functions? (hint: it has a magnetometer, like many AHARS) ;-)

RalphInCA said:
So, is this an actual problem? Can those airplanes actually crash with no GPS? Or is it an "abundance of caution" thing.
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If you see the list of things that were lost with dual GPS loss of signal, it's a cascading shopping list of stability augmentation, pilot relief (autopilot) modes, and envelope protection. Losing those systems on most airplanes (can't speak specifically to the Embraer) would not bring it down immediately but would increase the workload to keep it flying, probably by a lot under some conditions. It sounds like a lot of faults tied to a system the manufacturer has no control over, with the subject GPS NOTAMs a case in point.

Nauga,
who knows solar flares always win
 
zaitcev said:
You're thinking about a different problem. Suppose that an airplane was flying straight for 1110 km, then turned 90 degrees left. If AHARS weren't constantly correcting for vertical, the EFIS would then show a 10 degree bank.
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I see the problem, but I don't see the connection to Goddard's rocket. His error was that the feedback turned with the correction, a fatal stability error. This error is related to curvature of the earth.

It could be solved very easily without a GPS with a simple inclinometer and long-duration low pass filter and some outlier rejection. That's essentially how a conventional "iron" AI works. Perhaps augmented by a GPS when available; Kalman filters are not at all new technology.
 
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wow Phenom. Your aircraft enters a degraded mode of flight with the loss of GPS? It is like you are channeling the current generation of new pilots into your fundamental aircraft design. What an embarrassment. I christen you the "hyundai of the sky"…….
 
A lot of this is way over my head, but let me see if I'm getting it. The navigation system in this aircraft is so tightly related to the control surfaces on the airplane that when the navigation "source", GPS, fails or sends erroneos signals, the airplane's aileron's, elevator and rudder begin to behave in an unstable way?
 
luvflyin said:
A lot of this is way over my head, but let me see if I'm getting it. The navigation system in this aircraft is so tightly related to the control surfaces on the airplane that when the navigation "source", GPS, fails or sends erroneos signals, the airplane's aileron's, elevator and rudder begin to behave in an unstable way?
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It does not read that way. It reads like some systems fail or go offline but the surfaces still respond as expected to the inputs they get from the systems that remain functioning. You just appear to lose a lot of stuff intended to make the airplane easier to fly.

Nauga,
and a little pilot relief
 
nauga said:
It does not read that way. It reads like some systems fail or go offline but the surfaces still respond as expected to the inputs they get from the systems that remain functioning. You just appear to lose a lot of stuff intended to make the airplane easier to fly.

Nauga,
and a little pilot relief
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OK. The NOTAM says Phenom 300's should stay away because of "flight stability controls." I guess it's like the Airbus fly by wire thing with the addition of a reliable GPS signal being required for the computer to tell the control surfaces to do the right thing.
 
stratobee said:
They rely on the AHRS and GPS for all autopilot and stability. With that gone, you get autopilot fail, yaw damper fail, ventral rudder fail etc:

http://www.faa.gov/documentLibrary/media/Notice/GENOT_7110_711_EMB-300.pdf
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OK. ATC is being warned to expect speed reductions and Emergency Descents. Hopefully to many of these airplane's aren't in the air all at the same time. This isn't a good system. The whole "aviate, navigate, communicate" thing is getting skewed. Now you need accurate NAV signals to "aviate." Hopefully these Phenom 300's get fixed and whatever idea got it to this point dies.
 
luvflyin said:
OK. The NOTAM says Phenom 300's should stay away because of "flight stability controls." I guess it's like the Airbus fly by wire thing with the addition of a reliable GPS signal being required for the computer to tell the control surfaces to do the right thing.
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Sometimes the terminology gets convoluted but the failure description talked about stability augmentation dropping offline. That doesn't mean it starts providing spurious inputs, it means it turns off and you're left without (e.g.) a yaw damper. It still seems like a pretty weak link to go from GPS fail to stall warning/envelope protection and yaw damper failures. Would be interesting to see the logic path that led to this.

Nauga,
watering the fault tree
 
If we can have GA aircraft with 3 axis autopilots not dependent on GPS, why exactly is there a passenger jet that doesn't have that as a default AP mode?
 
ircphoenix said:
If we can have GA aircraft with 3 axis autopilots not dependent on GPS, why exactly is there a passenger jet that doesn't have that as a default AP mode?
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It's a business jet. So it is GA. Maybe not what you are thinking of, when you say GA, but there's a lot in common, as its avionics are based on Garmin 1000 or 3000.
 
nauga said:
It still seems like a pretty weak link to go from GPS fail to stall warning/envelope protection and yaw damper failures. Would be interesting to see the logic path that led to this.

Nauga,
watering the fault tree
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My only guess is that they just skimped on INS and/or gyro quality to save money, and used precise GPS state vectors (or whatever you engineers call them) to substitute or augment rather than the other way around.
 
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