GFC500 Update

[gsxrpilot]

I'm never been crazy about the requirement to have a G5 to go with the GFC500. I realize another option is the G3X, but I think it still has to have a backup AI of some sort.  I like the revisionary option of the Aspens. I don't have to have any screen that is there solely as a backup. But rather I have screens that are all useful, but can become an emergency back up when needed.

 

[donkaye]

7 hours ago, LANCECASPER said:

I still don't like the limitation of having to have a valid GPS signal to do a coupled approach of any kind in the GFC500. If there's a GPS outage it would be nice to fly a coupled ILS.

In the past 7 months of having the GFC 500, there has never been a time that an ILS has not been possible.

[LANCECASPER]

37 minutes ago, donkaye said:

In the past 7 months of having the GFC 500, there has never been a time that an ILS has not been possible.

Last Friday (1/24) there were GPS outages all over Texas.

 

[PT20J]

5 hours ago, gsxrpilot said:

I'm never been crazy about the requirement to have a G5 to go with the GFC500. I realize another option is the G3X, but I think it still has to have a backup AI of some sort.  I like the revisionary option of the Aspens. I don't have to have any screen that is there solely as a backup. But rather I have screens that are all useful, but can become an emergency back up when needed.

 

I worry that more and more equipment is dependent on GPS in one way or another and GPS is vulnerable to jamming by various means. I posted a link in another thread about an incident where GPS jamming caused an upset in a business jet when the GPS-aided AHRS went nuts and affected the yaw damper. 
 

Skip

[Bob - S50]

I've flown during a potential GPS outage in my area and did not notice any degradation in performance.  However...

Even with a GPS outage, you can still fly an ILS, you just can't couple the autopilot.  What I'm not sure about is whether or not the flight director would still work without the GPS.

But to your point, that is one reason we keep the KNS80 in our plane.  VOR/LOC/GS/DME.

[Ragsf15e]

9 hours ago, PT20J said:

I worry that more and more equipment is dependent on GPS in one way or another and GPS is vulnerable to jamming by various means. I posted a link in another thread about an incident where GPS jamming caused an upset in a business jet when the GPS-aided AHRS went nuts and affected the yaw damper. 
 

Skip

I think it’s really important for people to keep their hand flying skills strong while realizing that managing an autopilot during typical ifr flight is probably the safest way to operate.  In the very rare circumstance where you have a gps outage over an ifr field at altitudes that affect your autopilot, it’s time to use the hand flying skills.  That should not be the end of the world or even cause a second thought.  If it does, you probably shouldn’t be flying ifr... I use the autopilot all day long, but if I will crash the plane without it, I probably need to rethink my plan.

Has anyone actually had a gps outage in the terminal area/altitude of an ils equipped airport?  Outage areas expand with altitude, so that would mean the jamming is very close to the airfield.

[LANCECASPER]

12 hours ago, Ragsf15e said:

I think it’s really important for people to keep their hand flying skills strong while realizing that managing an autopilot during typical ifr flight is probably the safest way to operate.  In the very rare circumstance where you have a gps outage over an ifr field at altitudes that affect your autopilot, it’s time to use the hand flying skills.  That should not be the end of the world or even cause a second thought.  If it does, you probably shouldn’t be flying ifr... I use the autopilot all day long, but if I will crash the plane without it, I probably need to rethink my plan.

Has anyone actually had a gps outage in the terminal area/altitude of an ils equipped airport?  Outage areas expand with altitude, so that would mean the jamming is very close to the airfield.

I agree with all of that, but that has to do with pilot skills which should be kept continually sharp.

However, to build a GPS-required-for-a-coupled-ILS-approach into the autopilot seems like a design flaw or shortfall of the GFC500 to me, since that is not a limitation of the GFC600. It makes me wonder what other shortcomings it has.

[Emmet]

... or it might make adaption and certification for different airframes a lot easier and helps keep system costs down ...

As always with engineering it all depends on which parameters you are optimizing for and there are always tradeoffs - not necessarily design flaws ..

I have compared tracks of approaches from KFC150 KFC200 and the GFC500 and the GFC is way ahead.

[LANCECASPER]

2 hours ago, Emmet said:

... or it might make adaption and certification for different airframes a lot easier and helps keep system costs down ...

As always with engineering it all depends on which parameters you are optimizing for and there are always tradeoffs - not necessarily design flaws ..

I have compared tracks of approaches from KFC150 KFC200 and the GFC500 and the GFC is way ahead.

No doubt, if you got a good installation from an experienced shop, a new installation of a digital autopilot is going to follow a track very closely. 

However, a good installation of GPS Steering on a legacy autopilot like a KFC 150 or KFC200 will sharpen the track up a lot for a fraction of the price of a new autopilot. The key with the legacy autopilots is to only let a shop that really knows those units touch them. People that don't know them well can really mess things up.  Make sure they align the autopilot with the attitude source with a King break-out box.

[donkaye]

4 hours ago, LANCECASPER said:

However, a good installation of GPS Steering on a legacy autopilot like a KFC 150 or KFC200 will sharpen the track up a lot for a fraction of the price of a new autopilot. The key with the legacy autopilots is to only let a shop that really knows those units touch them. People that don't know them well can really mess things up.  Make sure they align the autopilot with the attitude source with a King break-out box.

I had a new "transitioning to a Bravo" student yesterday whose KFC 150 autopilot with the KAS 297 altitude preselect was oscillating down descents in a "bumping" kind of way, similar to some KFC 200 autopilots that I have flown that oscillate in a "bumping" fashion when in level flight.  He was going to take it to an autopilot shop to get it fixed for probably beaucoup AMUs.  Having apparently solved my oscillating descents on the GFC 500 by lubing the yoke and elevator finings, I decided to try that on his airplane.  Well, what do you know, the oscillations stopped.  In hindsight, this all makes sense.  Resistance to movement of the servos, however slight, can cause undesirable effects.  Now I'm wondering if my wing rock in my old KFC 150 could have been stopped with a little lubrication of the aileron linkages and yoke?

[donkaye]

Say what you may about the new generation of autopilots, having the LVL button and envelope protection is a major improvement over the legacy autopilots.  As the technology races ahead, I wouldn't be surprised to see the one button auto landing available for our airplanes in the next 10 years.

Yes, I wasn't happy that the GFC 500 had GPS aiding for an ILS approach, but that has turned out to be a non issue so far, and the benefits of this autopilot far, far outweigh the negatives.  I personally even like the G5 as a backup.  

[PT20J]

7 hours ago, donkaye said:

I had a new "transitioning to a Bravo" student yesterday whose KFC 150 autopilot with the KAS 297 altitude preselect was oscillating down descents in a "bumping" kind of way, similar to some KFC 200 autopilots that I have flown that oscillate in a "bumping" fashion when in level flight.  He was going to take it to an autopilot shop to get it fixed for probably beaucoup AMUs.  Having apparently solved my oscillating descents on the GFC 500 by lubing the yoke and elevator finings, I decided to try that on his airplane.  Well, what do you know, the oscillations stopped.  In hindsight, this all makes sense.  Resistance to movement of the servos, however slight, can cause undesirable effects.  Now I'm wondering if my wing rock in my old KFC 150 could have been stopped with a little lubrication of the aileron linkages and yoke?

Excellent point, Don. The Mooney control system has an abundance of rod ends that are supposed to be lubricated with Triflow annually. The aileron control tubes pass through guide blocks that should be inspected and lubricated annually. Control column shafts pass through blocks that can add fiction, and a little silicone lube is good here from time to time. The elevator trim system has a lot of different lubrication points. Often pilots think their trim servo is bad because it can no longer overcome the friction of a poorly maintained trim system. All the lubrication details are in the service manual. It is important to do a control check before each flight and note excessive friction in any system — including manually checking the elevator trim.

No pilot enjoys flying an airplane that has excessive control breakout force due to friction, and the autopilot also doesn’t perform well in that situation. Also, poorly lubricated control system components wear and create slop that manifests as a dead zone. Autopilots don’t like that much, either.

Skip

[gsxrpilot]

What lube should be used on the yoke shaft?

[Ragsf15e]

20 hours ago, LANCECASPER said:

I agree with all of that, but that has to do with pilot skills which should be kept continually sharp.

However, to build a GPS-required-for-a-coupled-ILS-approach into the autopilot seems like a design flaw or shortfall of the GFC500 to me, since that is not a limitation of the GFC600. It makes me wonder what other shortcomings it has.

Price.

[MIm20c]

1 hour ago, gsxrpilot said:

What lube should be used on the yoke shaft?

I use the squeeze bottle tri flow. Works well but does need to be reapplied every 6 months or so to keep it really slick. 

[PT20J]

22 hours ago, LANCECASPER said:

However, to build a GPS-required-for-a-coupled-ILS-approach into the autopilot seems like a design flaw or shortfall of the GFC500 to me, since that is not a limitation of the GFC600. It makes me wonder what other shortcomings it has.

I think it's a function of the AHRS. The low cost AHRS that are showing up in everything from portable devices to transponders as well as, of course, flight instruments depend on GPS to control drift. Without a valid GPS signal, the MEMS sensors will start to drift off in a few minutes.

[EricJ]

8 hours ago, PT20J said:

I think it's a function of the AHRS. The low cost AHRS that are showing up in everything from portable devices to transponders as well as, of course, flight instruments depend on GPS to control drift. Without a valid GPS signal, the MEMS sensors will start to drift off in a few minutes.

I don't think that's completely true.   The $15 AHRS that you can buy for a Stratux does pretty well without a GPS input.   I haven't done any very long-term tests, but I've not seen it lose track of attitude in a noticeable way.   I've used the gyros in an old phone to drive an attitude indicator app without gps and it did fine.

I don't know what drives the "need" (if there is one) to connect GPS to an attitude reference, since position and attitude are independent.   In the past I've been on projects where GPS was used to update accelerometer-derived position estimates, because those will accumulate drift over time, but you don't need that to fly an ILS.  

[Bob - S50]

I look at it this way.

How many times have I lost my GPS signal (zero)?  What is the likelihood I will (pretty slim to almost nil)?  In the unlikely event that happens am I willing to take the chance that I might actually have to hand fly an approach (oh the horrors) in exchange for saving several thousand dollars (yes)?

The most likely scenario under which I'll lose my GPS signal is that my GTN650 decides to pack it in.  If that's the case I've also lost my #1 ILS anyway so I'll be hand flying off my KNS80 displayed on a CDI.

Life is full of risks.  I find this one to be acceptable.

Edited February 3, 2020 by Bob - S50

[PT20J]

2 hours ago, EricJ said:

I don't think that's completely true.   The $15 AHRS that you can buy for a Stratux does pretty well without a GPS input.   I haven't done any very long-term tests, but I've not seen it lose track of attitude in a noticeable way.   I've used the gyros in an old phone to drive an attitude indicator app without gps and it did fine.

I don't know what drives the "need" (if there is one) to connect GPS to an attitude reference, since position and attitude are independent.   In the past I've been on projects where GPS was used to update accelerometer-derived position estimates, because those will accumulate drift over time, but you don't need that to fly an ILS.  

You may well be right. I just note that more and more avionics seem to be dependent on GPS in one way or another. I don’t lose a lot of sleep over it, but it clearly is a single point of failure for a lot of stuff. Apparently, the FAA is concerned enough to keep a skeleton VOR network in place and maintain airports with non-GPS instrument approaches.

https://www.faa.gov/air_traffic/flight_info/aeronav/acf/media/Presentations/18-02-VOR-MON-Status-Update-EEtienne.pdf

So, I still maintain MON capability with a KX165 connected to a dedicated nav/ILS indicator and a DME. So, if GPS is unavailable, or the GNS430W tanks, or the PFD goes dark I can get down the old fashioned way.

Skip

[Ragsf15e]

On 2/1/2020 at 9:48 PM, LANCECASPER said:

I agree with all of that, but that has to do with pilot skills which should be kept continually sharp.

However, to build a GPS-required-for-a-coupled-ILS-approach into the autopilot seems like a design flaw or shortfall of the GFC500 to me, since that is not a limitation of the GFC600. It makes me wonder what other shortcomings it has.

I think this has everything to do with the g5 and not really the gfc500.  The g5 controls the gfc and is the brains.  The g5 also requires gps to aid the attitude solution.  It doesn’t go “red x” or totally fail attitude without gps, but it is slightly degraded.  The old aspens used pitot/static to aid attitude solution and they did “red x” with a clogged pitot.  Anyway, I doubt they could certify a precision approach capability with even a slightly degraded attitude solution which the g5 has without gps.

Maybe when the -275 can control a gfc500 it won’t have that gps requirement for an ils?  Anyone know what a -275 uses to aid it’s ahrs attitude solution?  

What about the gfc600... does it have its own ahrs or use input from a g500?  What kind of aiding if any does it’s attitude solution use?

[LANCECASPER]

17 minutes ago, Ragsf15e said:

I think this has everything to do with the g5 and not really the gfc500.  The g5 controls the gfc and is the brains.  The g5 also requires gps to aid the attitude solution.  It doesn’t go “red x” or totally fail attitude without gps, but it is slightly degraded.  The old aspens used pitot/static to aid attitude solution and they did “red x” with a clogged pitot.  Anyway, I doubt they could certify a precision approach capability with even a slightly degraded attitude solution which the g5 has without gps.

Maybe when the -275 can control a gfc500 it won’t have that gps requirement for an ils?  Anyone know what a -275 uses to aid it’s ahrs attitude solution?  

What about the gfc600... does it have its own ahrs or use input from a g500?  What kind of aiding if any does it’s attitude solution use?

It can use a variety of inputs. 

http://static.garmin.com/pumac/190-01488-00_B.pdf

[Ragsf15e]

19 minutes ago, LANCECASPER said:

It can use a variety of inputs. 

http://static.garmin.com/pumac/190-01488-00_B.pdf

No doubt, but the important part is where it gets its attitude solution... the gfc600 has its own attitude source in the controller.

From the gfc600 manual “The GMC 605 contains internal sensors which calculate the aircraft attitude, allowing the GFC 600 to operate without relying on any external source of attitude. Flight Director mode logic as well as some autopilot management functions are performed within the GMC 605 main processor.”

[LANCECASPER]

1 minute ago, Ragsf15e said:

No doubt, but the important part is where it gets its attitude solution... the gfc600 has its own attitude source in the controller.

From the gfc600 manual “The GMC 605 contains internal sensors which calculate the aircraft attitude, allowing the GFC 600 to operate without relying on any external source of attitude. Flight Director mode logic as well as some autopilot management functions are performed within the GMC 605 main processor.”

Yes!  By the time you add all of the options to the GFC500 including the needed G5 it's not that much more for the GFC600, a much more sophisticated autopilot with more robust servos.

Now if only they would add Mooney to the AML.

[Ragsf15e]

Just now, LANCECASPER said:

Yes!  By the time you add all of the options to the GFC500 including the needed G5 it's not that much more for the GFC600, a much more sophisticated autopilot with more robust servos.

I guess I just don’t see any issues with either of them.  There will always be tradeoffs or have we found the perfect airplane or avionics?  I use to fly the F-15E with 50,000lbs of thrust.  It was awesome, but could sometimes be a “pig” at heavy weights or high altitude, so they upgraded the engines to give another 5,000lbs each.  You know what, the pilots said it was awesome, but it would be even better with even more thrust!  We will never settle for what is available, we’ll want more.

I would be happy to have a gfc500 and I think they did pretty good with the cost vs capability tradeoff.  If you want to wait for the gfc 600 to be certified for us (if ever) and pay a little more for a little more capability, that’s your decision, but I guarantee even the gfc600 made tradeoffs, so there’s probably something there we could find to complain about.

[LANCECASPER]

I am not looking for something to complain about. If I didn't have an autopilot I may consider a GFC500 , but taking out an autopilot that is able to fly a coupled ILS without GPS and then spending that much money and not being able to fly a coupled ILS during a GPS outage would be a step backwards in capability for me so I wouldn't even consider it - a complete non-starter. If the GFC600 is approved someday for Mooney it would be nice to have envelope protection and a true digital autopilot with internal AHRS (very close to the GFC700) and I would carefully consider it.

There was a thread about this awhile back on Beechtalk and sadly many people who had already spent the money and installed a GFC500 didn't even realize that it had that limitation. It was a complete surprise to them. It would be nice to know that limitation before you attempted it in IMC during an already disconcerting GPS outage.