Notam by FAA after the military jammed the GPS signal in southern California. The GPS/AHRS controls autopilot, yaw dampening, ventral fin dampening. stall warning system etc. Bizarre. Sometimes it’s nice to have good old steam..
Notam
Interesting…
How is that it uses the GPS signal for the stall warning system?!
That is IMHO impossible, because everybody knows that GPS signal is sometimes not there.
There is an issue but it is a bit more specific: GPS input is used by Garmin to their AHRS, to deliver a certified primary pitch/roll reference. See multiple threads here on e.g. Aspen or G1000 failure with loss of pitot tube (airdata) or GPS, respectively.
What is true for all GA including bizjets (except for the very top end ones) is that the plane cannot navigate usefully without GPS.
Only INS gets you out of that hole, but that’s pricey – a few hundred k I believe, for certified bizjet products.
Actually it is an interesting question to ask what a G1000 plane would do if there is no GPS when you start up. The G1000 cannot deliver a certified pitch/roll then.
The question is, what is so specific to the Phenom 300 to issue such kind of warning only for that model?
I would presume that a lot more aircraft models use a identical setup for their AHRS drift correction.
The G1000 obviously needs GPS to function “fully”, but it does not need GPS for attitude indication provided that it still has airdata/magnetometer – it needs one of the two available in addition to the AHRS.
Coolhand wrote:
How is that it uses the GPS signal for the stall warning system?!
I would guess GPS is used to check the stall warning inputs (AOA / Airspeed).
Coolhand wrote:
The question is, what is so specific to the Phenom 300 to issue such kind of warning only for that model?
It mentions the tendency for dutch roll, this could be unique to this aircraft. Peter wrote:
Actually it is an interesting question to ask what a G1000 plane would do if there is no GPS when you start up. The G1000 cannot deliver a certified pitch/roll then.
It will give a LOI annunication on startup as well as AHRS GPS annunciation.
Peter your link to the older thread suggested you wouldn’t lose AI/DG PFD functions if you lost GPS on the G1000. Agree you need GPS for FPL and other functions.
Not sure why the Phenom is affected. AoA, ADC, AHRS and yaw damper don’t need GPS surely?
Jesse most swept wing aircraft have the yaw damper on the MEL due to dutch roll, I doubt the Phenom is any hotter in this department than the Lear. YD failure in flight requires a descent to a lower max operating altitude, not sure about an emergency descent as mentioned in the NOTAM.
Jesse wrote:
I would guess GPS is used to check the stall warning inputs (AOA / Airspeed).
How can it do that? It only knows the ground speed. The Phenom 300 uses two “Goodrich Smartprobes” for pitot/static and AoA measurement: http://utcaerospacesystems.com/cap/systems/sisdocuments/Air%20Data%20Products%20and%20Systems/SmartProbe%28R%29%20Air%20Data%20Systems.pdf
I would guess that this problem is caused by a software error (or rather faulty software design) which puts too much emphasis on the GPS data. I wonder how this was not discovered during certification where failure of the GPS receiver of loss of GPS signal must have been considered.
what_next wrote:
How can it do that? It only knows the ground speed. The Phenom 300 uses two “Goodrich Smartprobes” for pitot/static and AoA measurement:
I do not know these probes, nor do I known this aircraft. As they do with other pitot protection systems, it works that the GPS and / or AHRS feels quite some movement for a while, when their is no airspeed. In these cases systems would give a check pitot heat / pitot blocked etc. annunciation.
The loss of GPS (or AHRS) would render this check impossible. This system might be called the stall warning protection system on this aircraft.
All avionics issues are “normal” for a full loss of GPS and could be expected. I think the major issue is that the aircraft no longer flies stable, but tends to yaw and roll.
RobertL18C wrote:
AoA, ADC, AHRS and yaw damper don’t need GPS surely?
Depending on the system design, this dependency is normal for AOA, ADC and AHRS. Not sure on Yaw damper.
RobertL18C wrote:
Jesse most swept wing aircraft have the yaw damper on the MEL due to dutch roll, I doubt the Phenom is any hotter in this department than the Lear.
Sure, but it might be unexpected to the crew, that a loss of GPS will take out the yaw damper. A Learjet might use a different system. Again, I don’t know these aircraft, but can see why systems are designed as such.
It gives the GPS depency topic another kick. We all are quite depended on this technology, and shows that a complete GPS of all GPS units onboard can be a real issue.