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

http://www.faa.gov/documentLibrary/media/Notice/GENOT_7110_711_EMB-300.pdf

by a-no-n • 10 years ago

80 45 10 years ago

smegel• 10 years 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_exer2• 10 years 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

JshWright3• 10 years 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_exer2• 10 years 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• 10 years ago

How much oscillation? On a scale from "bumpy ride" to "holy shit my wing's off".

JorgeGT• 10 years 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-n3• 10 years ago

http://forums.jetcareers.com/threads/emb-300-phenom-yaw-damp...

a-no-n3• 10 years ago

Another pilot forum also https://www.pilotsofamerica.com/community/threads/gps-interf...

taspeotis• 10 years ago

And on HN: https://news.ycombinator.com/item?id=11856131

rsync• 10 years ago

Translation: we never tested flight with the GPS off.

raverbashing6• 10 years 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-damp... ) shows

mmanfrin• 10 years ago

Can someone provide context?

a-no-n3• 10 years 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_...

1. http://www.ainonline.com/aviation-news/business-aviation/201...

2. http://static.garmin.com/pumac/778_InstallationManual.pdf

3. http://static.garmin.com/pumac/1152_GRS77_GMU44Troubleshooti...

kaffeemitsahne• 10 years ago

What would be the purpose of this outage?

JshWright3• 10 years ago

It appears that the Embraer Phenom 300 has GPS so deeply integrated into its "flight control computer" that the loss of GPS results in the loss of a number of important systems, including the system that prevents a common aerodynamic instability, known as "Dutch Roll".

Modern planes aren't flown directly by people. They're flown by computers, with people using the controls in the cockpit to tell the computer what they want the plane to do (there is no direct link between the stick/yoke and the flight surfaces). The computer integrates all the information at its disposal and determines what movements of the flight control systems are necessary to meet the pilot's commands (this is known as fly by wire). In this case, it seems that computer is _really_ dependant on GPS.

jsmthrowaway3• 10 years ago

(there is no direct link between the stick/yoke and the flight surfaces)

Almost true and oft-repeated. There are still means to somewhat control most FBW aircraft in the unlikely event all electrical control is lost; A320 can pitch/yaw with mechanical linkage to stabilizer trim and the rudder, for example (but, to your point, neither involve the sidestick). The flight is very likely headed for an unpleasant end but the intent is to buy time to restore computer control. Landing with trim, rudder, and differential thrust alone is possible (some have landed with less), but it's a big ask for a pilot accustomed to automation.

That scenario aside, when a whole lot of things fail an Airbus can also go into a mode called Direct Law, which basically tells the computer to take a hike and puts the pilot in direct control of surfaces proportional to airspeed (and puts structural integrity in jeopardy, because the computer isn't helping to obey design limits). The aircraft is extremely sensitive in this configuration.

(If you saw Sully recently, one of the reasons he quickly started the APU was to prevent the aircraft from leaving the relative safety of Normal Law in the absence of electrical power. This was described in the report, if I recall, and was one of the more critical decisions made.)

Boeing is entirely different in FBW philosophy from Airbus. A coarse summary might be that Airbus drivers are negotiating with a computer while Boeing drivers are generally flying the airplane. Both have merits and drawbacks and vocal camps.

dfsegoat3• 10 years 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_...

MichaelGG• 10 years 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.

dfsegoat3• 10 years 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.

raverbashing6• 10 years ago

These jets cannot fly without GPS.

No need for FUD. Loss of Yaw Damper is not something that would endanger an aircraft

dfsegoat3• 10 years ago

tried to edit it. but why would they mention it so prominently in the NOTAM?

dogma1138• 10 years ago

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

0xcde4c3db• 10 years 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• 10 years 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.

raverbashing6• 10 years ago

who did the avionics, by the way?

Garmin

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

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