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_...
No need for FUD. Loss of Yaw Damper is not something that would endanger an aircraft
My interest was more to the weapons system testing itself.
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.
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.
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...
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
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.
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.
Garmin
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
Damn.
