I understand your point, but it’s a matter of learning it. Once done, you don’t really mix it, and actually on SEP, there is very limited difference between DME and GPS distance.
If the GI275 is a concern for dual failure, why not get an additional G5 as the backup? Or another totally different brand which has a battery?
In most commercial airliners and smaller planes, backup ADI’s are mostly of a totally different brand than the main cockpit or at least completely isolated from the rest by independent power source.
In our GA planes, we have a lot of issues with that: Most of those only have one pitot. So if that one gets stuffed or iced, no more airspeed. Some EFIS take issue with that, primarily the Aspens pre Max but I hear also others.
However, the most important thing you need to have when the cockpit goes dark ist attitude. Loss of control without attitude indicators is unfortunately a very common thing to occurr, partial panel skills nonwithstanding. The other bit is, if you have 2 ADI’s and one goes bad, the big question is which one is right. At night, in IMC and possibly snowfall which I personally think is the worst distraction you can have visually, that could be fatal.
So from a point of view of redundance:
- EFIS of your choice, doesn’t really matter which one.
- 2ndary ADI either electric with battery or vaccum.
- 3rd ADI battery driven with charge by the airplane.
My own setup is an Aspen, a vaccum ADI and a Dynon D1.
The aspen may fail even due to airspeed loss. The vaccum ADI and the Dynon are not impacted by that. If the vaccum one packs up, I can verify the Aspen ADI via the Dynon. If I have a total electrical failure, both Aspen and Dynon deliver ADI information via battery and the vaccum will run until the engine stops.
Clearly, the Dynon does not have airspeed, but shows GPS Alt and GS. Again, that is better than nothing, but needs consideration. Altitude is relatively benign in that regard but speed must be more or less ignored unless you know your wind very precisely.
The other redundancy bit which many people forget about is COM. I have a YAESO FTA750 which can be connected to the outside com antenna. That thing also features a basic GPS and full ILS display.
As for position backup, I suppose everyone has either an IPAD or other portable GPS on board. Even a mobile can do that job these days. Some apps even have the possibility to display an EFIS of their own, but that requires an AHRS sensor which must be battery driven if it is to serve in case of electrical. Such a setup imho could replace a D1 or similar, but personally I think the D1’s set and forget attitude is really nice in case of cases.
Redundancy is a tricky subject and planning it for an avionics upgrade should include consideration of the various failure scenarios, as suggested by @Mooney_Driver. Given the reliability of most of the modern stuff, portable may be the most economical option and get the job done even if not perfect compared to in-panel redundancy. Just comparing multiple devices vs a single EFIS screen unit oversimplifies a lot. With only one static and pitot system as is the case with almost all SEP, if the system fails for whatever reason all connected devices go u/s at some point in time. Having 1, 2, 3, or 10 GI275’s won’t change the results all that much, even if degradation is limited and gradual due to AHRS, GPS, etc.
chflyer wrote:
chflyer29-Oct-23 12:1853
Redundancy is a tricky subject and planning it for an avionics upgrade should include consideration of the various failure scenarios. Comparing multiple devices vs a single EFIS screen unit oversimplifies a lot. With only one static and pitot system as is the case with almost all SEP, if the system fails for whatever reason all connected devices go u/s at some point in time. Having 1, 2, 3, or 10 GI275’s won’t change the results all that much.
There´s probably a reason why IFR certification only requires 1 pitot tube on SEP´s (operationally: limited to commercial VFR only). I would think that the risk of failure of the single, non icing conditions, single pitot static system is very slim – compared to the risk of a single failure, single instrument (vacuum or electric). in 28 years of flying I´ve seen some failed vacuum driven and electric driven flight instruments, but I have never experience a pitot static system failure (other than in simulators!).
So, multiple displays (with back up possibility), obviously does provide display redundancy – in particular if their function is not related to shared inputs. The back up AI/ADI is a good example.
chflyer wrote:
portable may be the most economical option and get the job done
I totally agree on that – as a practical approach, but then that screws up a nice looking glare shield.. I´ve got a Dynon 2 permanently installed (the airplane came with it) and it´s not pretty, I don´t fly IFR (on my aircraft), but whatever happens, it sits there and I would be comfortable using it unplanned, in addition to the vacuum driven 50 year old ADI!
@Yeager I’ve had a pitot failure this year. The short hose piece going from the pitot tube to the metal tubing inside the wing ripped off. Luckily it happened on ground and was clearly identified prior to making a takeoff.
My interpretation was that it happened because we used the pitot heat a lot. Standard procedure for instrument flight is to switch on pitot heat on departure point. I assume that pitot heat hasn’t been used a lot in the past 30 years on that plane and that this weakened the rubber hose. Additionally it wasn’t actually placed well. It was too long and bent, that was where it came off.
Luckily, we identified it instantly, and repair is plain easy. It is just put over the respective metal connector…
One might consider that regarding pitot failure modes. I’m glad to know that my PFD will continue on GPS speed if the pitot should fail.
johnh wrote:
johnh24-Oct-23 17:1044
It’s pretty good for flying approaches. You just point the end of the syn vis tunnel at the runway and keep it pointed there. No need for anything else. (Only used it for one flight, in a G1000 equipped C182).
There is a reasonably good example of SVS with Flight Path Vector and ILS combination on the youtube link here:
The (FPV) is pointing on the synthetic 3D Runway Symbiology.
What is not very clear, most of the time in the video, is that in the lower center part of Primary Flight Display (PFD) no 1 (left side display) it the lateral deviation indicator (localizer in this approach), and the Glide Slope Indication, is indicated in green (mid/upper/right hand side).
Just as a matter of interest, the Head Up Display (HUD) of course also has the FPV which the pilot will point in real world picture onto the Runways (or any other reference pointing the aircraft).
Peter wrote:
Peter24-Oct-23 21:5948
We did that topic before here. Good Q: what nav system do you use? The ILS instrument, or SV? You can’t really use both…
This would depend on the display technology of course. As seen above, both the instrument navigation indicators and the SVS is displayed simultaneously on the same display. Needless to say, only the instrument navigation indicators are legal for use, the SVS is only for added awareness.
The truth is – the simplest thing is point with the FPV, as soon as your on the established Glide Path Angle (as per the ILS/RNAV/GPS approach flown).
UdoR wrote:
@Yeager I’ve had a pitot failure this year. The short hose piece going from the pitot tube to the metal tubing inside the wing ripped off. Luckily it happened on ground and was clearly identified prior to making a takeoff.
I´ve been away from the light GA world for a couple of decades, but I just don´t recall pitot probes to be a point of failure, as opposed to many other typical IFR systems/instruments. Maybe it´s more common that I recall – but I though they were simple systems with extremely low failure rate.
As you correctly point out, in your failure case, this could be related to an abnormal usage, such as using the pitot heater a lot after decades of not being used.
Yeager wrote:
There´s probably a reason why IFR certification only requires 1 pitot tube on SEP´s
Some jurisdictions require IFR approved RVs to have two pitot tubes
example:
from system architecture standpoint the requirement makes some sense for a “fully” redundant cockpit: PFD is connected to pitot on the left hand site while MFD to the other one
RV14 wrote:
Some jurisdictions require IFR approved RVs to have two pitot tubes
example:
Which jurisdictions would that be? out of curiosity.
