G3X to IFR

I've been IFR certified for 15 years now and I never intended to use my RV-4 for serious cross countries, but missions change, and I am now and I'd like to file IFR. The honest reason, Options are safety and I prefer flying any cross-country "in the system". I just find it easier. Also, my G3X has 2-axis A/P and I find simulated "hood" (with a safety pilot in the back) very easy and intuitive with this system.

I can read the regulations just as well as you all, and I know I only have a single gyro in my G3X. I've installed w/serial-coupling an INS-429 (ILS/VOR) which is legit en-route. If I installed a second gyro that should do it good to sign the logbook "capable of IFR" and start filing.

My question is this... Does it make more sense to install the backup battery and second gyro to the G3X or do I install a totally separate display, G5 of D10 and use the essential batter/bus on my ExpBus?

Opinions, experiences and thoughts welcome.

Thanks,

I love the functionality and warm and fuzzy the G5 offers. Not only is it a backup display, it is also a backup gyro- It will feed your G3X should your primary AHRS fail. It's also got an optional battery to last you way too long while you're depending on it. For the price, you cannot beat this as a solution. IMHO.

I’m sure you know, your G3X doesn't actually have any gyroscopes....
Legalese: if you have a relatively new version of Operating Limitations, it will say something like ‘IFR allowed if equipped per FAR 91.205’. If you have a G3X and nav capability ‘appropriate for the flight’ then you meet 91.205 now and may file IFR if the PIC is rated and current.
Real World: the FARs for EAB leave the PIC a lot of discretion when it comes to redundancy and backups (e.g., none are required by law). Some chose to fly ifr where a single failure (power buss, efis, etc) would leave them in a potentially fatal situation if in IMC. Others choose varying degrees of redundancy. If you have 2 attitude sources and they disagree, which is right? Maybe you need 3. Most of us have all-electric airplanes. What if the alternator fails? What if it’s the main battery? These choices are all left to the PIC. For myself, I chose to have 3 independent attitude sources on board, all from different manufacturers, running different (hopefully) software. I have one efis with its own standby battery. I have an iPad with WingX that can shoot a passible approach to at least non-precision minimums. I still just have one engine. It’s up to you to set your risk tolerance.

G5 Backup

BruceMe said:

I've been IFR certified for 15 years now and I never intended to use my RV-4 for serious cross countries, but missions change, and I am now and I'd like to file IFR. The honest reason, Options are safety and I prefer flying any cross-country "in the system". I just find it easier. Also, my G3X has 2-axis A/P and I find simulated "hood" (with a safety pilot in the back) very easy and intuitive with this system.

I can read the regulations just as well as you all, and I know I only have a single gyro in my G3X. I've installed w/serial-coupling an INS-429 (ILS/VOR) which is legit en-route. If I installed a second gyro that should do it good to sign the logbook "capable of IFR" and start filing.

My question is this... Does it make more sense to install the backup battery and second gyro to the G3X or do I install a totally separate display, G5 of D10 and use the essential batter/bus on my ExpBus?

Opinions, experiences and thoughts welcome.

Thanks,

Click to expand...

The G5 can serve as an independent, dissimilar, battery-powered backup attitude source to a G3X system. The independence and dissimilarity between the G5 and GSU 25 lessen the likelihood of a common mode failure between them.

As mentioned, in the rare event that you were to lose a GSU 25, the attitude information from the G5 would be cross-filled over to the GDU. For most aircraft, there is no reason to install more than one GSU 25 ADAHRS and a battery backed G5 backup instrument. With this combination it is extremely unlikely that you will ever find yourself without a primary flight instrument, and the G5 can independently operate the autopilot should the displays not be available.

Thanks,

Justin

g3xpert said:

For most aircraft, there is no reason to install more than one GSU 25 ADAHRS and a battery backed G5 backup instrument.

Click to expand...

Could you expand on the thinking behind this statement? I ask, because it is counter to the view that you need 3 attitude sources, in an IFR machine, so you can tell which one has failed. For example, if you have two and one indicates 20 degrees of bank and the other indicates wings level, which one do you believe? Perhaps the GSU 25 and/or the G5 can self check against GPS or perhaps the compass function is independent of the attitude?

Raiz said:

Could you expand on the thinking behind this statement? I ask, because it is counter to the view that you need 3 attitude sources, in an IFR machine, so you can tell which one has failed. For example, if you have two and one indicates 20 degrees of bank and the other indicates wings level, which one do you believe? Perhaps the GSU 25 and/or the G5 can self check against GPS or perhaps the compass function is independent of the attitude?

Click to expand...

IMO that's what a proper instrument scan and cross check is for.

Back ups, AP, Stratus

Apologize for the large pictures...Imgr newb...

G3X, G5 and Garmin autopilot...the auto pilot ?LVL? button is also a useful check to ?break a tie? since the Garmin autopilot (perhaps many others as well) include solid state attitude reference.

Cross check of heading, altitude, turn indicator etc in my instrument scan is invaluable.

Two examples. Both backed up by Stratus (second/third opinion) attitude reference.




Redundancy to the extreme...777...funds my hobbies...

I agree about the scan and cross check but that only works if the instruments are independent. With steam gauge six-pack, you could always work out which instrument had failed by looking at the set. You have the AI, turn and bank and the DI - all independent instruments that give you information about the roll angle or heading change.

What happens in a glass system? Are there separate sensors for each of these functions or are they integrated, such that a single failure could affect more than one function?

I'm still a fan of dual GSU25's and G5, you can make the MFD display ahrs2 while the PFD is on ahrs 1 and the G5 is source 3.

I also like that the G3X does a comparison between the 2 GSU's and lets you know if they disagree (it does not do that with the G5).

The most common failure mode is definitely losing the data and or power connection to the ADHRS sensor. In this mode, the display will raise a fault and X's all over the visuals effected. We've all see it when we run the GDU disconnected.

This picture looks like that failure exactly (G1000)...
https://www.euroga.org/system/1/user_files/files/000/029/849/29849/4b919de35/large/IMG_0753.JPG

Partial failure modes would be difficult to quantify and the manufacturers would have to chime in.

I have no idea what exactly is in the GSU 25D ADAHRS, but most commercial solid state gyro/accelerometers are one integrated "MEMS" circuit for all 6 axis. The 3-axis magnetometer is typically a separate IC chip on the same board.

Given there are 9-axis of measurement + barometer, there could be internal (software) integrity checks on reasonable values. Like you should only accellerate so fast and the magnetic field should be reasonably close to the gyro derived target heading and pitch.


So... I wouldn't even call this apples to oranges. This is like apples to apes. It's not even similar.

Raiz said:

What happens in a glass system? Are there separate sensors for each of these functions or are they integrated, such that a single failure could affect more than one function?

Click to expand...

The latter. Some time back there was a report here concerning a Dynon system, which uses pitot data to help reach an attitude solution. If it detects a pitot failure, it's suppose to auto-switch to GPS ground speed data. In this case there was a partial pitot blockage, but not enough to auto-switch to GPS. After a few minutes of flying, the airspeed was obviously low - and the horizon displayed by the AI was obviously (he was in VMC) wrong, too.

G5

I went with a G5, total redundancy, built-in emergency power, good integration, should work well. Now I have to find room.