You lost me on the grammar there – are there some words missing?
Two commas actually. Has Jan stolen your login?
Latin and words like fetish don’t really strengthen your arguments tomjnx. I am personally just interested in better understanding how these systems (and G1000 in particular) have been implemented in practice, and the design philosophy that was applied, so that I can fly them more safely and so that I can establish an appropriate balance of trust/cynicism in what they are showing me.
In my opinion, the problem with telling the pilot “this information might be wrong, figure out for yourself whether it’s OK or not”, is the human factors element. Your average pilot may not diagnose correctly, or may take too long to do so while in the meantime following false information. And that’s even assuming they notice the flag or warning. OTOH, if you say “sorry, I can’t give you attitude information, use the standby AI”, there is no pilot interpretation needed and the correct course of action if 100% clear.
That said I can understand your philosophy that “you can never have too much information” and that it may be useful to see the suspect attitude indication if you really need to, and are trained to use/ignore it appropriately.
9 gyro/accel/mag sensors is three angular rates that have to be integrated plus two vectors, one of which is known to be wrong during turns and must be ignored short term, so it doesn’t give the redundancy that “3 unknowns vs 9 measurements” suggests. I’m sure that Garmin wouldn’t have introduced the extra redundancy of ADC/GPS data if they were 100% confident that the other 9 sensors were sufficient on their own?
Two commas actually. Has Jan stolen your login?
The majority of EuroGA participants are non-UK and it may be easier to get the meaning across if one writes more text, preferably divided into some paragraphs. But I could not work out that sentence despite having lived in the UK since 1969.
Maybe we should charge a membership fee? 
ortac wrote:
Your average pilot may not diagnose correctly
If you distrust the “average pilot” to not interpret a flag correctly, you may as well get rid of pilots altogether. The only value IMO a human adds is the capability to cope with unforeseen circumstances.
ortac wrote:
one of which is known to be wrong during turns and must be ignored short term
It’s not wrong, it’s just the addition of the gravity vector with the acceleration vector.
And you propose to use IAS instead, which is (together with heading) a 2D vector which has no relationship the position or attitude of the aircraft in space. How exactly is this any better? (ok, in a supersonic fighter jet you can probably ignore wind most of the time, while the magnitude of the acceleration vector may well be more than g, but in a SEP or MEP it’s usually the other way round).
ortac wrote:
I’m sure that Garmin wouldn’t have introduced the extra redundancy of ADC/GPS data if they were 100% confident
Do you believe in proof by authority?
tomjnx wrote:
But again, I’m not per se against comparing data and presenting a figure of merit, but I’m very much against this figure of merit being used to hide information.
Wasn’t one of the criticisms related to AF447 that the PFD continued to show information even though the system identified it as unreliable? And the poor sap followed it instead of identifying the issue and performing the relevant SOP. I think they did some digging in this and found that other crews that encountered similar situations were slow to react. It might be a sign of a more sophisticated system but a big red X will certainly wake you up.
Peter wrote:
But I could not work out that sentence despite having lived in the UK since 1969.
If you have dual AHRS/ ADC installation, you can choose which your PFD uses. Typically the “left” (number one) unit will drive the left PFD and the “right” (number two) unit will drive the right PFD. If you have just one PFD, the second unit will be a backup (what else). Not sure how it would work with just one display (no MFD).
Peter wrote:
But I could not work out that sentence despite having lived in the UK since 1969.
The post was 100% clear to me 
Does this mean my English improves with each EuroGA usage?
Wasn’t one of the criticisms related to AF447 that the PFD continued to show information even though the system identified it as unreliable? And the poor sap followed it instead of identifying the issue and performing the relevant SOP. I think they did some digging in this and found that other crews that encountered similar situations were slow to react. It might be a sign of a more sophisticated system but a big red X will certainly wake you up.
However, the much bigger thing was IMHO that if those guys knew anything about the specific aircraft systems, they would have known that the pitch indication doesn’t need the pitot tubes (so “unreliable airspeed” was not relevant to the pitch indication) and pitch+power=speed so you can carry on. The problem is that most airline pilots don’t have that depth of avionics knowledge, and GA “glass” pilots have even less, on average.
Obviously many other factors came into play with AF447…
Does this mean my English improves with each EuroGA usage?
With the amount of time I spend on here, my English should be infinitely good
Peter wrote:
However, the much bigger thing was IMHO that if those guys knew anything about the specific aircraft systems, they would have known that the pitch indication doesn’t need the pitot tubes (so “unreliable airspeed” was not relevant to the pitch indication) and pitch+power=speed so you can carry on. The problem is that most airline pilots don’t have that depth of avionics knowledge, and GA “glass” pilots have even less, on average.
Well, frankly, which GA pilot would have pitched the nose up despite a horriffic sinkrate and the horizon showing a horriffic pitch up? What these guys were missing were the basic flying skills you normally learn before your first solo.
Clearly, some of the system logic of the A330 did not help, but the actual failure of the pitot lasted very shortly. It however got them and the system so badly confused that neither managed to recover in time to reckognize what the hell went on. 3 airline pilots do not reckognize a stall, are more afraid of overspeed than (obviously) falling out of the sky? Sorry.
I think AF447 had finally hit home with Airbus and their ideas about flight training. Maybe also about how such systems should work. there is NO need to include IAS into a pitch reference system and fail the same if IAS fails. that is one of the things I also don’t like about the Aspen and why I carry 2 extra horizons.
@Peter If you fail to notice the indication is unreliable, understanding of the system won’t help. They simply were not trained in high altitude, well, anything. IIRC they didn’t train loss of airspeed at high altitude, they didn’t train stall at high altitude, they didn’t train flying in alternate law at high altitude. At first, they didn’t know they lost airspeed and were in alternate law. And I think they didn’t trust inertial reference (attitude indication, etc.) later on either. SOP was pitch & power (with several settings for different altitudes, weights and configurations and there is simplified emergency procedure with just a few of them) and some housekeeping (making sure FD, auto-thrust, etc. are off, IIRC). Cruise really isn’t main focus of training.
I think review of similar incidents showed that other crews didn’t apply the SOP, some of them because they didn’t think it applied (either they didn’t consider the speed unreliable, just wrong, and/ or they didn’t perceive danger because they were up high) – all sort of funny business happened as a result. Also there was tendency to ignore stall warning in this situation. As I recall.
@Mooney_Driver We may never know why the PF continued to pitch up. He probably started because he was chasing an altitude loss, at least partly virtual because of the loss of air speed, which he didn’t know at the time that he lost, and attitude indication was affected by the turbulence I think at the time, it showed less pitch, so it might have look as if the plane pitched down a bit and lost some altitude, all the while trying to keep wings level as the turbulence was rolling the plane. There are plenty of possibilities. I just know it’s not a nice place to be – being truly confused, thrown into unexpected situation knowing you could soon die if you can’t figure it out. IIRC he wanted to climb before A/P disconnected (weather avoidance) and he was worried about overspeed. The first stall warning came in, I think, before they realized they were in alternate law, it might have been perceived as something that shouldn’t be happening, that doesn’t make sense. Brain has only limited capacity. I can understand how he might not have been able to process more information. Critical there was that it all happened very quickly. He was hamfisted with the stick when he tried to control the plane in turbulence. And the PNF went on to diagnose the issue instead of monitoring. And they failed as a crew. PNF repeatedly told PF to descend. He never did that, even though he acknowledged it.
