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All glass cockpit redundancy

DA40drvr wrote:

I had to use the GPS moving map, compass, standby AI (separately driven, electrical), standby altimeter to get down

Exactly the point my post was trying to make. The glass cockpits have very complex failure modes and now we see glass even for the backup. MD302 in the TBM 930, probably Garmin G5 next year and then you have the same software/logic running everywhere. There are a lot of inputs to those glass cockpits that can degrade in many different ways while the mechanical instruments just need a source of energy and Newton’s laws.

It is my view that this all glass setup is an order of magnitude less redundant than having a mechanical backup AI. I’m all for glass but not convinced about going all-Garmin-all-solid-state-all-glass even for the backup.

There could be a situation (electrical fire, etc) where you have to switch off all electrical equipment. In my case I use a Dynon D2 (GPS based) battery powered AI + DG. I also have had an altimeter failure at 400ft in the climb, cloudbase 200ft or less. Of course, since I had two altimeters, this was a non-event but it gets your attention.

EBKT

It is my view that this all glass setup is an order of magnitude less redundant than having a mechanical backup AI. I’m all for glass but not convinced about going all-Garmin-all-solid-state-all-glass even for the backup.

I agree, I used to instruct avionics redundancy on the airbuses (loved ATA24 btw) it’s clear that going all electric has its own complexities which can be far more difficult to fully comprehend then a simple mechanical back-up. Take this example for a year I was seeing intermittent failures on my Bo. GPS, EHSI, sometimes the radio even the Autopilot didn’t work 100%. It came down to a loose CB contact producing electrical arcing, which had a cascading effect and a variety of failures….Going all electric would mean to have at least two completely separate electrical generating systems and buses, with bus transfer or isolation capability plus redundancy in primary systems.
This is just the beginning not even talking single pitot, static lines etc..It all comes down to cost. Is this feasible in a GA aircraft?….I lost once the EHSI completely…luckily there was still Skydemon :-) and a full battery on the tablet :-). PS I love my old OAT mechanical Beech probe sticking out my windshield…at least it works correctly and I can see the ice building :-)

EBST

DA40drvr wrote:

If the magnetometer output is intermittent or differs significantly from the GPS direction then you lose the DI and attitude completely – apparently the G1000 decides it cannot work out whether the GPS or the AHRS is correct so it gives you neither. It also takes out the localizer and glideslope display on the PFD (and MFD, if switched to reversionary mode). So a magnetometer failure is a single point of failure (singe engine G1000). All you get is a big red X on the PFD.

I’ve had an (intermittent) magnetometer failure on a G1000 and I did not lose the AI, so it can’t be quite as simple as that. Also, there is no reason why you should lose the CDI and GS indications. Something more must have been going on in your case.

ESKC (Uppsala/Sundbro), Sweden

Agreed, the display shown by DA40drvr is an AHRS failure.

Think of the system when you first power-up. The GPS, in itself, has no idea in which direction the aircraft is pointing until you start moving. Your AHRS and (serviceable) magnetometer will be providing good information before taxi.

Last Edited by Dave_Phillips at 24 Oct 09:54
Fly safely
Various UK. Operate throughout Europe and Middle East, United Kingdom

I’ve always been flying glass (only 10 years flying) and honestly, in a crisis situation, I might get confused with these round gauges. I also expect failure rates are in favor of solid state over mechanical spinning vacuum stuff. As long as there’s no data connection and no source code shared between g3000 and standby, I’m happy to fly all glass.

Last Edited by loco at 24 Oct 09:57
LPFR, Poland

Dave_Phillips wrote:

Agreed, the display shown by DA40drvr is an AHRS failure.

Then the question is what did his second PFD show? G1000 has 2 separate AHRS.

Going off at a very slight tangent on what single component failure can cause total or massive electrical failure, I once had this on the HS125 (BAe125/Hawker).

To cut a long story short, it had a 28v system with two batteries in parallel. To start the engines, the batteries were placed in series to produce 56v. This process was managed by a relay.

We were at about V1 at London Gatwick at Cat I minima when that relay failed. It pumped 56v into everything, including all three inverters and all the backup equipment. Each bit of equipment failed in its own special way in its own time. The rest of the flight, with no radio, no navigation and weather at minima was not fun at all. This was way before the days of GPS, iPads etc. We had nothing, not even a handheld radio.

Shit happens, friends.

EGKB Biggin Hill

I also expect failure rates are in favor of solid state over mechanical spinning vacuum stuff.

Having been in electronics since I was about 6 I am sure that is very true, but it’s a bit like saying the chances of getting terminal cancer after a CT scan is 0.01% i.e. 100 people have died out of 1M scanned. The “problem” is that you might be one of those 100

And in electronics you never know… yesterday I had a UPS delivered; it lasted 1 second (with a 40W load) after the mains input was pulled out to test it. Some smoke came out… The failures of complex electronics are extremely complex; in say a GNS430 you have millions of single points of failure. The DOA (dead on arrival) rate of electronics is atrocious; laptops (across the range) are around 3%, and I don’t expect avionics to be much better, and I have first hand reports from the installer scene of €15k boxes having defective functions e.g. the VHF radio of a GNS/GTN/IFD (especially IFD) box not working when installed.

Also any number of factors might raise the chances dramatically e.g. a wire rubbing against something and wearing through after years. And if it rubs against just the right thing, you get a weird problem somewhere else.

So the debate will never be simple. The failure modes cannot be analysed, beyond the very obvious ones (the ones the software is written to deal with). That’s why one must always have a completely standalone backup for flying the plane in a basic way.

Administrator
Shoreham EGKA, United Kingdom

achimha wrote:

Then the question is what did his second PFD show? G1000 has 2 separate AHRS.

There is only one PFD (MFD can go to PFD in reversionary) and one AHRS (GRS77). There are two GPS, NAV/COM etc.

Last Edited by Dave_Phillips at 24 Oct 10:31
Fly safely
Various UK. Operate throughout Europe and Middle East, United Kingdom
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