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Posted
11 hours ago, M016576 said:

Really?  Or is it an input from a GPS that the GFC couples too... and the pilot sets the input.  On a 430W, from what I remember, you can load the gps with an ils approach... but it’s only for advisory- or you can switch it over to the actual approach (nav) and fly it the legal way.

seems silly that garmin would have its autopilot only able to couple to a GPS signal.. or worse- use a nav input that isn’t the primary nav input being flown (couple to gps when ils/nav is selected as primary).

Disclaimer- I don’t own any garmin stuff.

On the 530W, you get a big warning window saying "GPS for advisory only" if you haven't switched the ILS to the correct active frequency.  If you have, it will automatically switch from GPS to ILS when you come onto the approach course somewhere outside the GS intercept point.  IIRC, if at that point you switch to GPS (or never set the ILS on frequency), you only get LOC guidance, but no GS--the GPS hasn't done the LPV checks and so will not give you vertical guidance.

I don't understand how the GFC could use GPS guidance for an ILS approach, since the only way you would get vertical guidance is if the GPS source in question knew to do the LPV check sometime during the approach.

  • Like 2
Posted

Pure speculation on my part:
It doesn’t use it to fly the approach, it uses it to briefly maintain proper descent until error GS returns.
We really need Garmin to explain how they are using GPS .


Tom

Posted (edited)
9 hours ago, ArtVandelay said:

Pure speculation on my part:
It doesn’t use it to fly the approach, it uses it to briefly maintain proper descent until error GS returns.
We really need Garmin to explain how they are using GPS .


Tom

I think so- if that’s accurate... because it’s completely illegal by FAA standards to “fly” an ILS approach without any ILS reception!

im willing to bet it’s a misunderstanding of some sort though- I’d doubt a system could be certified that would claim to be shooting one type of approach, when in reality it’s shooting something else.  Stranger things have happened though...

Edited by M016576
Posted

One thing for sure...

1) There are many errors in each nav system that are being checked by the box or by the pilot...

2) You can’t check one system (raim check) Then fly the ground based ILS signal... that could leave you empty handed...

3) You can’t check the ILS viability (listen for the ILS specific audio) then assume the raim is good.... still empty handed...

4) if you are using GPS signals to navigate, make sure the raim is good...

5) if you are using ILS signals to navigate, make sure the ILS signal is good...

6) if you don’t know which one you are using... get some time with the manuals... or a CFII.... you decide.  :)

7) there isn’t a way for a nav box supplier to hide what source is being used to navigate. A simple outage could lead to a simple disaster....

I like the GPS signals... they are much straighter than VOR’s scallop shaped signals... either one can suffer having altered signals because of interesting local terrain...  ILSs have interesting multiple solutions based on wave length issues... you need to be really far off to have the other/alternative GS look right....

PP thoughts only, not a CFII...

Best regards,

-a-

Posted

Here is a quote from a Garmin rep on the Beechtalk forum about why you need the GPS to have the autopilot fly the ILS/LOC or VOR approach.  Please note, you can still hand fly the approach or, as noted, use other AP modes to fly the approach.  It just won't be coupled.

"The GFC 500 does support coupling to VOR/LOC/ILS ground based navigation sources, but it uses GPS data to improve autopilot performance.

This was posted back in September on another thread, but probably worth repeating.

The GFC 500 uses GPS data to significantly improve the often unruly signals received from ground based short range navigation systems. This is actually quite common for high performance autopilot systems.

A GFC 500 autopilot improving its VOR/LOC/ILS navigation guidance with GPS data will fly the aircraft with accuracy unheard of without this improvement.

Autopilots like the Garmin GFC 600 and GFC 700 are capable of flying coupled short range navigation even in the absence of GPS data, but performance is reduced and the complexity of tuning the autopilot system to be able to fly well using just the ground based navigation signal is extremely complex, often aircraft specific, and always time consuming.

In an effort to keep the GFC 500 autopilot performance consistently high, as well as affordable, and recognizing that GPS outages are almost always planned, and almost never affect approaches flown at airports, the GFC 500 requires GPS to couple to ground based navigation sources.

Keep in mind that even though you can't couple to VOR/LOC/ILS without GPS, you still have VOR/LOC/ILS green needles to fly with and perfectly good lateral/vertical autopilot modes that are not dependent on GPS.

As explained in the AFMS, in the unlikely event that GPS is lost, you may re-engage the autopilot in HDG (laterally) and PIT, ALT, or VS modes (vertically) to continue to fly the green needles in the absence of GPS. As soon as you fly out of the affected area, you can push the NAV button and re-engage with full capabilities."

  • Like 1
Posted

As as observed before, it sounds like their autopilot isn't good enough to fly without GPS guidance, which isn't confidence-inspiring to me.   So many other companies got GA autopilots to fly approaches with analog computers that I'm pretty puzzled how they lost that recipe.

I've done a lot of digital control system coding...which is typically just applying digital methods to analog control models.  It really sounds like they're admitting that they don't know how to do that.

 

Posted

Eric,  you have me thinking...  got any analog noises that you can’t eliminate from entering in your control system digital conversions?

 

Follow this logic... the digital world improving the already good enough analog world...

 

Sounds like...

A bunch of analog pilots... Discussing digital solutions... supported by some real digital guys... :)

 

When the equipment provider has added a digital solution on top of an analog  challenge... kind of combined a digital solution where the analog device has known challenges/deficiencies...  (they are known in some cases because the IAP says clearly that coupled approaches are not allowed...) :)

 

Looks like...

The equipment provider fails to deliver what it is they are actually doing. (As if mystery will sell the product better, a real marketing sales type challenge)

The analog pilot that believes everything on the ILS path is perfect all the time. Won’t recognize the technical control issues that are being solved by this digital solution to an old analog problem...

 

Could have been...

old APs reacted so slowly... the analog anomaly on the glide path appeared to get ignored.... as it would actively get ignored by a pilot hand flying the plane...

New APs have the ability to react pretty quickly... a real problem when analog guidance has some real noise in the glide slope.

 

Might be...

With digital brains, the nav box can filter out anything that isn’t the intended straight line... (not too complex?)

 

The new microchips being delivered for AI and complex grapghics solutions are a combination of analog and digital.... (much more complex?)

For examples of driverless car technology today... Nvidea is building some pretty impressive chips... (Buy The chips, not the stock lately :))

 

For big G to explain this at the level that reaches every pilot, is quite a challenge...

 

To benefit from this logic... one would need to have an ILS coupled approach system... and use it often, to many different airports, around the country... to see how big a challenge this really is, or isn’t....

 

To See an example of a similar situation check out the development work the Cies guys had to do to smooth out the data being delivered from the analog, fuel level floats, through the digital, sender, to the digital instrument in the panel... smoothing the very noisy data caused by the real fuel sloshing in the tanks...

The digital overlay to a good float system improved the data from being off by a couple of gallons to being within tenths of a gallon... while in turbulence...

Nice to have on most days... a real have to have when things aren’t going so well...

 

Eric, got any a big noises in your control systems? Like A big mountain in your way?  :)

My control system experience has been pretty noise free... temperature control and motor speeds... any noises got filtered out before they got to the controls...

 

Pp thoughts only, thinking out loud, not a controls technician, engineer, or sales guy...

Best regards,

-a-

 

Posted
2 hours ago, EricJ said:

As as observed before, it sounds like their autopilot isn't good enough to fly without GPS guidance, which isn't confidence-inspiring to me.   So many other companies got GA autopilots to fly approaches with analog computers that I'm pretty puzzled how they lost that recipe.

I've done a lot of digital control system coding...which is typically just applying digital methods to analog control models.  It really sounds like they're admitting that they don't know how to do that.

 

That's not what he said.  To me it sounded like he said that without GPS smoothing, the autopilot would be yanking and banking to follow a less than perfect ILS.  He also said they do build two that don't need the GPS (600 and 700) but they won't do as well as the 500 with GPS aiding.  He then went on to say that they calculated the risks and determined that most of us CSOB's would rather get a great autopilot for half the cost and live with the limitations.  I agree.

I wish people would stop bad-mouthing the GFC500.  IF YOU DON'T LIKE IT DON'T BUY IT.

Of the new autopilots (TT, Trio, Garmin):

Garmin is the ONLY one that can fly the ILS.

Garmin is the ONLY one that is certified to fly a coupled approach.

Dynon says you can fly an ILS, but who knows when that will be available and it costs just as much or more than the Garmin.

If you prefer an old STEC or King, then by all means get one.  As for me, for half the cost, I'll take the Garmin.  And for what it's worth, our KFC200 would frequently S turn down final so it wasn't exactly perfect either.

  • Like 1
Posted
2 hours ago, carusoam said:

Eric,  you have me thinking...  got any analog noises that you can’t eliminate from entering in your control system digital conversions?

 

Follow this logic... the digital world improving the already good enough analog world...

 

That was kinda my point, that a digital implementation should be *at least* as good as an analog implementation.   When they have to explain that their digital implementation has to be aided by GPS or it isn't good enough, I think that's a step backwards in implementation.   IMHO a ball got dropped somewhere.

 

8 minutes ago, Bob - S50 said:

That's not what he said.  To me it sounded like he said that without GPS smoothing, the autopilot would be yanking and banking to follow a less than perfect ILS.  He also said they do build two that don't need the GPS (600 and 700) but they won't do as well as the 500 with GPS aiding.  He then went on to say that they calculated the risks and determined that most of us CSOB's would rather get a great autopilot for half the cost and live with the limitations.  I agree.

That's what I took it to mean he said as well.   My analog Century III doesn't "yank and bank", if I understand what you mean, on a less than perfect ILS, because the control loops are engineered into the aircraft system to not do that.   You can do the same with a digital implementation, and you should be able to do it at least as well as the analog implementation with the same inputs.   I'm puzzled as to why they can't do it, but perhaps the most obvious explanations may be that they don't know how to do it effectively or that their hardware is incapable.   This reduces my confidence in their system so that I am inclined to follow your advice and not purchase one, even though I'm in the market and it would otherwise be an obvious candidate.

There's certainly nothing wrong with using GPS data, when available, to augment an ILS or LOC approach, and it is the obvious thing to do when you can.   It should definitely improve performance and safety in the presence of a faulty ILS/LOC system when done properly.   But when the GPS is not available I don't know why the system shouldn't just revert to being the usual ILS/LOC approach autopilot navigator.   Not being able to do that seems fishy to me, especially when loss of GPS is a real consideration.

  • Like 1
Posted

Sorry I lost my temper and yelled.

It's good to know the limitations of each system so we can make an informed decision.  It's another to call it a bad system because of those limitations.

It's good to know that:

Garmin:  You need a GPS signal to fly a coupled ILS/LOC/VOR approach.  That the only time you can have the autopilot engaged below 800' AGL is during a coupled approach.  That the basic minimal system (1 G5/GMU11/GAD29 and two servos) will cost about $10,000 + install.

TT:  That you cannot engage the autopilot below 700(?) AGL.  That it is capable of, but cannot legally fly a coupled GPS approach.  That it is not capable of flying an ILS/LOC/VOR approach, legally or not.  That it does not offer a yaw servo or trim servo.  That it does not offer a flight director.  That it cannot do VNAV.  That you can have this for half the cost of the Garmin, about $5000 + install because you can use it with any ADI/HSI you want or already have.   If you want the G5 for an ADI then the cost difference drops to about $2000.

Trio:  That it has essentially the same limitations as the TT and for about the same cost.

They probably all work great as long as you can live with the limitations.  We all need to be informed and RTFM.

Posted
35 minutes ago, Bob - S50 said:

 

They probably all work great as long as you can live with the limitations.  We all need to be informed and RTFM.

And if you can't then you can go to an STEC or King starting at about 20k(Since all signs point to the GFC600 not coming to Mooneys). This is the first time in certified aviation that we're really starting to see autopilot options other than what the aircraft was originally certified with, presumably because the low cost options are doing things like GPS aiding so they don't have a multi year certification with each airframe and make their money back by bundling the AP with the aircraft. Up until a few years ago the only aftermarket option was usually the STEC line at some stunning prices.

Posted

My STEC scallops a lot when tracking a localizer.  I think the GFC500 autopilot using GPS to smooth the signal tracking is a brilliant solution that doesn't cost $30K.

Posted

Interesting how increased capability and safety is a no-go for some.  I can tell you that in the Beech 400 I fly, coupled, the A/P will fly a LNAV/VNAV(plane is not LPV certified) like it is on rails.  Coupling the ILS/LOC all depends on the airfield and the conditions of flight.  Sometimes it is spot on, others especially with wind/turbulence it is OK.  I would never couple a VOR or TAC, the A/P hunts and over corrects.  I can out fly the A/P on every approach accept on the RNAV.

So with the GFC500, I CAN fly any approach in the book and I MAY have to hand fly, but only if GPS is down.  Oh the horrors.

  • Like 2
Posted
My STEC scallops a lot when tracking a localizer.  I think the GFC500 autopilot using GPS to smooth the signal tracking is a brilliant solution that doesn't cost $30K.


Andy, curious which STEC you have (I have an STEC 60-2). I have never seen much scalloping with a localizer but will say that the localizer is less stable than an RNAV approach. I agree the GFC 500 is probably smoothing the localizer. Probably adding in wind corrections.

Here is a short video with me tracking the localizer while executing a coupled RNAV approach (the ILS is on the right hand HSI). I wish I recorded the coupled ILS approach I flew right after this approach. There was a little more course correction due to the winds aloft but you can see the ILS is rock solid on this approach. I do not believe the STECs use any GPS information when flying a localizer approach.




Sent from my iPad using Tapatalk Pro
  • Like 1
Posted

If you overlayed a RNav approach with the same mins over and ILS, and the plane flew both (perfectly) would their track (and angle) be identical?  

I am not talking about an offset ILS, but a standard one.

Posted

Chris- I have an STEC 50.  My first M20C had an STEC30, my Piper Aztec also had an STEC 50.  They were all very comparable to my current one, which was just at the factory for overhaul about a year ago. The 30 and the 50 are really less expensive versions of the 60-2 and have no vertical modes other than altitude hold.

In perfect conditions with no wind and a strong localizer signal it does really well.  Anything other than that and it hunts 5° left and right, even in APPR mode.  Of course it's worse tracking a VOR signal far from the station.

  • Like 1
Posted

I remember a couple of shops telling me that the 60 series was the best of the units available for GA. Said it was even better than the 55 series. Have flown in planes with the 55 series and I tend to agree.

I am curious to see how the 3100 compares to the GFC series as well as other offerings.


Sent from my iPhone using Tapatalk Pro

Posted (edited)
4 hours ago, Bryan said:

If you overlayed a RNav approach with the same mins over and ILS, and the plane flew both (perfectly) would their track (and angle) be identical?  

I am not talking about an offset ILS, but a standard one.

Depends on the approach, but I wouldn't count on it.    The LPV approach to Rwy 5 at KCGZ was recently changed to better align with the ILS approach to the same runway.   This helps "the stack", the training holding procedure at the Stanfield (TFD) VOR so that managing the holding altitudes was easier and safer.   Previously the approach entry altitudes were different, so people would exit "the stack" at different altitudes to enter the approach.   This made it a little tricky sometimes to sort out when people exited the stack.   Now with the profiles the same for either approach it is more straightforward.

So the procedures don't necessarily align.   This one was changed because of the large amount of traffic cycling through the stack every day.

Edited by EricJ
  • 3 years later...
Posted

On this week's episode of Opposing Bases (ATC/Pilot podcast), one of the hosts claimed that in 5 years we will be treating ILS equipment like we treat VORs (and NDBs and four course ranges): as historical equipment. Expensive and complex to maintain. 

 

Posted
1 hour ago, rbp said:

On this week's episode of Opposing Bases (ATC/Pilot podcast), one of the hosts claimed that in 5 years we will be treating ILS equipment like we treat VORs (and NDBs and four course ranges): as historical equipment. Expensive and complex to maintain. 

 

I would not be surprised. 

Posted
On 2/3/2019 at 7:46 AM, kpaul said:

couple a VOR or TAC, the A/P hunts and over corrects

my KFC225 flies like its on rails, no matter the approach

Posted
4 minutes ago, rbp said:

speaking of digital -- it seems that Canada wants to move away from magnetic to true headings.  the magenta line doesn't care! 

https://www.navcanada.ca/en/news/blog/switching-to-true-pulling-away-from-magnetic-north.aspx

Admittedly, the fact that they have the magnetic north pole in their country is a pretty reasonable argument, but I'm pretty sure the rest of the world might not agree.  Except maybe people in Antarctica?

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