8 ms·

Embraer Phenom 300 yaw damper fail due to loss of GPS signal [pdf]

80 points by a-no-n 10y ago

smegel 10y ago
> VENTRAL RUDDER FAIL, YAW DAMPER FAIL, AUTO PILOT FAIL, AND CAS MESSAGES ASSOCIATED WITH UNEXPECTED ROLLING AND YAWING OSCILLATIONS (DUTCH ROLL) AT HIGH AIRSPEEDS Damn.
throwaway_exer 10y ago
I have a commercial rating. The HN title is wrong. What this is saying: 1) If you don't have a yaw damper, then you'll have a rough ride 2) because the autopilot will induce oscillation (dutch roll) after loss of GPS
- JshWright 10y ago
  The HN title is literally the subject of the notice, very slightly paraphrased (abbreviations expanded, etc), so you may want to let the FAA know they got it wrong... I also think you misread the notice. The report is stating the loss of GPS apparently resulted in the subsequent loss of a number of other systems, including the yaw damper.
  - throwaway_exer 10y ago
    I think you're right. The wording about "no yaw damper" would have been clearer as "failed yaw damper" - I guess that's what was meant.
- Filligree 10y ago
  How much oscillation? On a scale from "bumpy ride" to "holy shit my wing's off".
  - JorgeGT 10y ago
    Dutch roll is characterized by a low frequency oscillation, with a period in the order of seconds. So it wouldn't be a "bumpy" ride but a slooow yet continuous, very nauseating oscillation (try to slowly rock forward and backward in your chair).
a-no-n 10y ago
http://forums.jetcareers.com/threads/emb-300-phenom-yaw-damper-fail-due-to-unreliable-or-unavalible-gps-signal.234746/page-2 http://forums.jetcareers.com/threads/emb-300-phenom-yaw-damp...
- a-no-n 10y ago
  Another pilot forum also https://www.pilotsofamerica.com/community/threads/gps-interference-testing-affecting-biz-jets.95388/ https://www.pilotsofamerica.com/community/threads/gps-interf...
  - taspeotis 10y ago
    And on HN: https://news.ycombinator.com/item?id=11856131 https://news.ycombinator.com/item?id=11856131
rsync 10y ago
Translation: we never tested flight with the GPS off.
- raverbashing 10y ago
  Planes are not built by "stuff.js" hackers I'm afraid And it does work without GPS, as this link (which was posted in this page http://forums.jetcareers.com/threads/emb-300-phenom-yaw-damper-fail-due-to-unreliable-or-unavalible-gps-signal.234746/page-2 http://forums.jetcareers.com/threads/emb-300-phenom-yaw-damp... ) shows
mmanfrin 10y ago
Can someone provide context?
- a-no-n 10y ago
  There was a cancelled, very large proposed GPS outage (NOTAM) centered on NAWS China Lake which specifically warned that the EMB-505 Phenom 300 business jet specifically should avoid operating in the Western US during this mysterious GPS outage/jamming test event.[0] Pressure from the AOPA and others likely contributed to the scrubbing of this would-be very large outage.[1] It turns out that the EMB-505 300 lateral stability at high speed is extremely dependent on GPS. Folks on the forums suspect the root cause is related to the Garmin GRS 77/GMU 44 AHRS part of the Garmin Prodigy G3000 package.[2,3] 0. https://www.faasafety.gov/files/notices/2016/Jun/CHLK_16-08_GPS_Flight_Advisory.pdf https://www.faasafety.gov/files/notices/2016/Jun/CHLK_16-08_... 1. http://www.ainonline.com/aviation-news/business-aviation/2016-06-10/aopa-military-scrubs-planned-gps-interference-testing http://www.ainonline.com/aviation-news/business-aviation/201... 2. http://static.garmin.com/pumac/778_InstallationManual.pdf http://static.garmin.com/pumac/778_InstallationManual.pdf 3. http://static.garmin.com/pumac/1152_GRS77_GMU44TroubleshootingReference.pdf http://static.garmin.com/pumac/1152_GRS77_GMU44Troubleshooti...
  - kaffeemitsahne 10y ago
    What would be the purpose of this outage?
    - colechristensen 10y ago
      "China Lake is the United States Navy's largest single landholding, representing 85 percent of the Navy’s land for weapons and armaments research, development, acquisition, testing and evaluation (RDAT&E) use and 38 percent of the Navy’s land holdings worldwide. In total, its two ranges and main site cover more than 1,100,000 acres (4,500 km2), an area larger than the state of Rhode Island."
    - deleted 10y ago
      [deleted]
dfsegoat 10y ago
This is a known issue - and old issue. These jets cannot fly without GPS. When they (the military) knocked out GPS intentionally around China Lake NAS a few months back (for testing aircraft in GPS denied environments) -- all Embraers were told to avoid the area: THIS NOTAM APPLIES TO ALL AIRCRAFT RELYING ON GPS. ADDITIONALLY, DUE TO GPS INTERFERENCE IMPACTS POTENTIALLY AFFECTING EMBRAER PHENOM 300 AIRCRAFT FLIGHT STABILITY CONTROLS, FAA RECOMMENDS EMB PHENOM PILOTS AVOID THE ABOVE TESTING AREA AND CLOSELY MONITOR FLIGHT CONTROL SYSTEMS DUE TO POTENTIAL LOSS OF GPS SIGNAL. https://www.faasafety.gov/files/notices/2016/Jun/CHLK_16-08_GPS_Flight_Advisory.pdf https://www.faasafety.gov/files/notices/2016/Jun/CHLK_16-08_...
- MichaelGG 10y ago
  Do you have any links to the reasoning that would let this kind of system be allowed? It seems rather fragile - GPS can be messed with rather easily.
  - dfsegoat 10y ago
    I have none -- I don't claim to know much more than that about Embraer (or any other type). I found it to be ridiculous as well. My interest was more to the weapons system testing itself.
- raverbashing 10y ago
  > These jets cannot fly without GPS. No need for FUD. Loss of Yaw Damper is not something that would endanger an aircraft
  - dfsegoat 10y ago
    tried to edit it. but why would they mention it so prominently in the NOTAM?
    - raverbashing 10y ago
      I'd say because aviation is risk averse and if a condition will impact a certain type or model of aircraft it is not going to be omitted (the fact that it's a smaller aircraft might imply in having some certification differences as well)
dogma1138 10y ago
How does an aircraft gets certified with out an INS for stability control?
0xcde4c3db 10y ago
Anyone have a sense of what the primary failure is here? Is there some Kalman filter that gets out of whack when an error term can't be calculated, or what?
Animats 10y ago
What a mess. We botched GPS/AHRS integration in our 2005 Grand Challenge vehicle. Seen this type of problem. Here's the problem. You have an Attitude and Heading Reference System (AHRS) with three rate gyros and three accelerometers, plus a magnetometer as a compass. From this information, you want to get aircraft orientation and heading. Integrating the rate gyros gives orientation, but because you're integrating a rate, there's cumulative error over time. The accelerometers give you a down reference. Not always a good one. Some AHRS units will lose their down reference if you fly in a circle for a while, and the accelerometers see a consistent but wrong "down" direction from centrifugal force. So AHRS systems are prone to cumulative error accumulation. You also have a GPS system, which is prone to short-term noise but does not accumulate cumulative error. GPS is position only; there's no orientation info from GPS. (There are some multiple-antenna GPS systems that get orientation, but those are rare) So AHRS/GPS systems try to combine the two using various filters. Those filters embody assumptions about the error properties of each system. Fusion of the two sources provides position information, with the GPS fixes being augmented with short-term info from the AHRS. However, it's possible for GPS position to "jump" due to radio propagation problems. You see this on smartphones all the time. It's not as bad for aircraft, which usually have a clear view of the sky. (It's much harder for ground vehicles, which can't always see enough GPS satellites. We had a lot of trouble with this in 2005.) The important outputs are attitude (pitch, roll, and yaw) which drive the artificial horizon ball (or, today, a graphic which looks like one). There's also heading, which drives the compass. The attitude outputs also drive the aircraft's stability control systems. The AHRS data can be used raw, or combined with GPS data to get not only attitude but position. Usually, the AHRS outputs are used without GPS info to drive the aircraft systems that just need attitude. But the fused AHRS/GPS data is usually better, and dealing with inconstencies between the unaugmented AHRS info and the fused data is a pain. So there's a temptation to use the fused data for everything. Embraer apparently did this. There's an argument for source integration. Air France 447 crashed because they lost airspeed and altitude data when the pitot tubes and static ports froze up. An integrated AHRS/GPS system would have given them accurate info on vertical speed and altitude even without air sensors. So integration isn't fundamentally a bad idea. If you integrate sources, though, you have to deal with sensor conflicts. That's a hard problem. Filters alone will not do it. The integration used by Embraer (who did the avionics, by the way?) apparently doesn't handle GPS failures properly. The AHRS is still there, and that's all you need for aircraft stability. But if the fused outputs are used for stability augmentation, stall warning, and such, apparently they can fail when the GPS data does.

80 points by a-no-n 10y ago

> VENTRAL RUDDER FAIL, YAW DAMPER FAIL, AUTO PILOT FAIL, AND CAS MESSAGES ASSOCIATED WITH UNEXPECTED ROLLING AND YAWING OSCILLATIONS (DUTCH ROLL) AT HIGH AIRSPEEDS Damn.

throwaway_exer 10y ago

I have a commercial rating. The HN title is wrong. What this is saying: 1) If you don't have a yaw damper, then you'll have a rough ride 2) because the autopilot will induce oscillation (dutch roll) after loss of GPS

JshWright 10y ago
The HN title is literally the subject of the notice, very slightly paraphrased (abbreviations expanded, etc), so you may want to let the FAA know they got it wrong... I also think you misread the notice. The report is stating the loss of GPS apparently resulted in the subsequent loss of a number of other systems, including the yaw damper.
- throwaway_exer 10y ago
  I think you're right. The wording about "no yaw damper" would have been clearer as "failed yaw damper" - I guess that's what was meant.
Filligree 10y ago
How much oscillation? On a scale from "bumpy ride" to "holy shit my wing's off".
- JorgeGT 10y ago
  Dutch roll is characterized by a low frequency oscillation, with a period in the order of seconds. So it wouldn't be a "bumpy" ride but a slooow yet continuous, very nauseating oscillation (try to slowly rock forward and backward in your chair).

a-no-n 10y ago

http://forums.jetcareers.com/threads/emb-300-phenom-yaw-damper-fail-due-to-unreliable-or-unavalible-gps-signal.234746/page-2 http://forums.jetcareers.com/threads/emb-300-phenom-yaw-damp...

a-no-n 10y ago
Another pilot forum also https://www.pilotsofamerica.com/community/threads/gps-interference-testing-affecting-biz-jets.95388/ https://www.pilotsofamerica.com/community/threads/gps-interf...
- taspeotis 10y ago
  And on HN: https://news.ycombinator.com/item?id=11856131 https://news.ycombinator.com/item?id=11856131

rsync 10y ago

Translation: we never tested flight with the GPS off.

raverbashing 10y ago
Planes are not built by "stuff.js" hackers I'm afraid And it does work without GPS, as this link (which was posted in this page http://forums.jetcareers.com/threads/emb-300-phenom-yaw-damper-fail-due-to-unreliable-or-unavalible-gps-signal.234746/page-2 http://forums.jetcareers.com/threads/emb-300-phenom-yaw-damp... ) shows

mmanfrin 10y ago

Can someone provide context?

a-no-n 10y ago
There was a cancelled, very large proposed GPS outage (NOTAM) centered on NAWS China Lake which specifically warned that the EMB-505 Phenom 300 business jet specifically should avoid operating in the Western US during this mysterious GPS outage/jamming test event.[0] Pressure from the AOPA and others likely contributed to the scrubbing of this would-be very large outage.[1] It turns out that the EMB-505 300 lateral stability at high speed is extremely dependent on GPS. Folks on the forums suspect the root cause is related to the Garmin GRS 77/GMU 44 AHRS part of the Garmin Prodigy G3000 package.[2,3] 0. https://www.faasafety.gov/files/notices/2016/Jun/CHLK_16-08_GPS_Flight_Advisory.pdf https://www.faasafety.gov/files/notices/2016/Jun/CHLK_16-08_... 1. http://www.ainonline.com/aviation-news/business-aviation/2016-06-10/aopa-military-scrubs-planned-gps-interference-testing http://www.ainonline.com/aviation-news/business-aviation/201... 2. http://static.garmin.com/pumac/778_InstallationManual.pdf http://static.garmin.com/pumac/778_InstallationManual.pdf 3. http://static.garmin.com/pumac/1152_GRS77_GMU44TroubleshootingReference.pdf http://static.garmin.com/pumac/1152_GRS77_GMU44Troubleshooti...
- kaffeemitsahne 10y ago
  What would be the purpose of this outage?
  - colechristensen 10y ago
    "China Lake is the United States Navy's largest single landholding, representing 85 percent of the Navy’s land for weapons and armaments research, development, acquisition, testing and evaluation (RDAT&E) use and 38 percent of the Navy’s land holdings worldwide. In total, its two ranges and main site cover more than 1,100,000 acres (4,500 km2), an area larger than the state of Rhode Island."
  - deleted 10y ago
    [deleted]

dfsegoat 10y ago

This is a known issue - and old issue. These jets cannot fly without GPS. When they (the military) knocked out GPS intentionally around China Lake NAS a few months back (for testing aircraft in GPS denied environments) -- all Embraers were told to avoid the area: THIS NOTAM APPLIES TO ALL AIRCRAFT RELYING ON GPS. ADDITIONALLY, DUE TO GPS INTERFERENCE IMPACTS POTENTIALLY AFFECTING EMBRAER PHENOM 300 AIRCRAFT FLIGHT STABILITY CONTROLS, FAA RECOMMENDS EMB PHENOM PILOTS AVOID THE ABOVE TESTING AREA AND CLOSELY MONITOR FLIGHT CONTROL SYSTEMS DUE TO POTENTIAL LOSS OF GPS SIGNAL. https://www.faasafety.gov/files/notices/2016/Jun/CHLK_16-08_GPS_Flight_Advisory.pdf https://www.faasafety.gov/files/notices/2016/Jun/CHLK_16-08_...

MichaelGG 10y ago
Do you have any links to the reasoning that would let this kind of system be allowed? It seems rather fragile - GPS can be messed with rather easily.
- dfsegoat 10y ago
  I have none -- I don't claim to know much more than that about Embraer (or any other type). I found it to be ridiculous as well. My interest was more to the weapons system testing itself.
raverbashing 10y ago
> These jets cannot fly without GPS. No need for FUD. Loss of Yaw Damper is not something that would endanger an aircraft
- dfsegoat 10y ago
  tried to edit it. but why would they mention it so prominently in the NOTAM?
  - raverbashing 10y ago
    I'd say because aviation is risk averse and if a condition will impact a certain type or model of aircraft it is not going to be omitted (the fact that it's a smaller aircraft might imply in having some certification differences as well)

dogma1138 10y ago

How does an aircraft gets certified with out an INS for stability control?

0xcde4c3db 10y ago

Anyone have a sense of what the primary failure is here? Is there some Kalman filter that gets out of whack when an error term can't be calculated, or what?

Animats 10y ago

What a mess. We botched GPS/AHRS integration in our 2005 Grand Challenge vehicle. Seen this type of problem. Here's the problem. You have an Attitude and Heading Reference System (AHRS) with three rate gyros and three accelerometers, plus a magnetometer as a compass. From this information, you want to get aircraft orientation and heading. Integrating the rate gyros gives orientation, but because you're integrating a rate, there's cumulative error over time. The accelerometers give you a down reference. Not always a good one. Some AHRS units will lose their down reference if you fly in a circle for a while, and the accelerometers see a consistent but wrong "down" direction from centrifugal force. So AHRS systems are prone to cumulative error accumulation. You also have a GPS system, which is prone to short-term noise but does not accumulate cumulative error. GPS is position only; there's no orientation info from GPS. (There are some multiple-antenna GPS systems that get orientation, but those are rare) So AHRS/GPS systems try to combine the two using various filters. Those filters embody assumptions about the error properties of each system. Fusion of the two sources provides position information, with the GPS fixes being augmented with short-term info from the AHRS. However, it's possible for GPS position to "jump" due to radio propagation problems. You see this on smartphones all the time. It's not as bad for aircraft, which usually have a clear view of the sky. (It's much harder for ground vehicles, which can't always see enough GPS satellites. We had a lot of trouble with this in 2005.) The important outputs are attitude (pitch, roll, and yaw) which drive the artificial horizon ball (or, today, a graphic which looks like one). There's also heading, which drives the compass. The attitude outputs also drive the aircraft's stability control systems. The AHRS data can be used raw, or combined with GPS data to get not only attitude but position. Usually, the AHRS outputs are used without GPS info to drive the aircraft systems that just need attitude. But the fused AHRS/GPS data is usually better, and dealing with inconstencies between the unaugmented AHRS info and the fused data is a pain. So there's a temptation to use the fused data for everything. Embraer apparently did this. There's an argument for source integration. Air France 447 crashed because they lost airspeed and altitude data when the pitot tubes and static ports froze up. An integrated AHRS/GPS system would have given them accurate info on vertical speed and altitude even without air sensors. So integration isn't fundamentally a bad idea. If you integrate sources, though, you have to deal with sensor conflicts. That's a hard problem. Filters alone will not do it. The integration used by Embraer (who did the avionics, by the way?) apparently doesn't handle GPS failures properly. The AHRS is still there, and that's all you need for aircraft stability. But if the fused outputs are used for stability augmentation, stall warning, and such, apparently they can fail when the GPS data does.