How good is your autopilot ?

[Joe Larussa]

So I'm fairly new to the autopilot scene. I have a Garmin 530 non Waas, HSI and S-tec 60. Shot the ILS today and wasn't blown away by the accuracy. Used the GPS all the way till I was established on final which was amazing. Then switched over to the ILS and it was a bit all over the place on the localizer and glide slope. What kind of accuracy can you expect or does it need some adjustment? Wouldn't say the auto pilot is nailing the what the HSI has to say.

[Danb]

Joe I personally would expect your stec to be rock solid on the ILS.

I have an stec 55x and it is extremely solid and accurate in all configurations.

[carusoam]

Joe, can you mention what your airspeed and ground speed was?  This may come up in the discussion...

Best regards,

-a-

[Piloto]

I have the 530AW coupled to the Century 31 AP. The Century 31 will fly an LPV or an ILS approach all the way down to the numbers, even with crosswinds. The only thing I control is the power to slow down. Very happy with it.

José 

[Joe Larussa]

8 minutes ago, carusoam said:

Joe, can you mention what your airspeed and ground speed was?  This may come up in the discussion...

Best regards,

-a-

Pretty much a no wind evening so airspeed and ground speed was about 100 MPH

[carusoam]

Some things to consider...

From the IR training drawing: One dot on the ILS is measured in feet.

A non-WAAS navigator provides a really smooth and straight line to follow.  (Compared to scalloped patterns of VORs).

How many dots off did your AP go?

From Dan's comment, I would expect centered on the middle dot is normal...

There is a particular approach angle on some ILS receiver antennas that are known to cause some issues from shadowing.

More things that come to mind, while waiting for somebody that knows better than me...

Best regards,

-a-

[Joe Larussa]

9 minutes ago, carusoam said:

Some things to consider...

From the IR training drawing: One dot on the ILS is measured in feet.

A non-WAAS navigator provides a really smooth and straight line to follow.  (Compared to scalloped patterns of VORs).

How many dots off did your AP go?

From Dan's comment, I would expect centered on the middle dot is normal...

There is a particular approach angle on some ILS receiver antennas that are known to cause some issues from shadowing.

More things that come to mind, while waiting for somebody that knows better than me...

Best regards,

-a-

Good things to consider. The few times I've shot the same ILS I have been right of course and off by about a needles width on the HSI. Didn't look at the GPS at the time. I bet if I ride the GPS signal it will plant me on the numbers.

[carusoam]

Unfortunately the non-WAAS GPS doesn't meet vertical guidance requirements...  

The good thing is, you are stepwise going through what works and what is close to working.  The 530 has various internal receivers (GPS,VOR,ILS) with different antennae attached to it.  Could be a cleaning of the various connections or antenna grounds or a check-up by a radio shop familiar with the Big G(?)

In this case, it may be more antenna and receiver than AP.  Consider also comparing the AP's ability to track various courses and compare to the magenta line on the IPad. This is something I did when my plane was new to me.  I found out how scalloped the VOR radials really are and how fabulous my non-WAAS GPS is.

Best regards,

-a-

[rbridges]

I'm sure someone with more expertise can correct me, but IIRC the autopilot follows the course differently with GPS and ILS.  I think it leads to a more direct course for the GPS whereas the HDG function following the localizer is more of a "fly and react/correct" setting.

[carusoam]

RB,

Good point.  The APCH mode is tighter and choppier compared to the NAV mode's smoother and looser control algorithm.

Best regards,

-a-

[M20F]

14 hours ago, Joe Larussa said:

Then switched over to the ILS and it was a bit all over the place on the localizer and glide slope. 

I have an S-Tec 50 and so can only do a localizer which if you get it lined up and then hit approach it works great.  If you are not lined up it will find its way to being lined up but it is a bit jerky in doing so.  Likewise if I hit altitude hold pitched for a 500 FPM climb it will remember I said hold 5000' and work its way to it but it pitches around until speed/pitch/alt/etc. all eventually stabilize.  So in my case if I get the localizer dialed in using heading bug and then hit APP no issues, likewise level and spin the trim wheel a bit and then hit ALT hold no issues.  

[Glenn]

The STEC is rate based and therefore sensitive to yaw.  If you try to help with the rudders, the way many of us learned to make small adjustments on the localizer, you can induce unwanted behavior.  I had the same problem on my first approach after installing my 55X.  The autopilot settled down once I stopped unconsciously  trying to help.

[cliffy]

One item to consider might be what traffic was ahead of you and what kind of traffic was taxiing near the LOC shed. Especially on CAT III ILS approaches (granted its called a "Capture ILS System and not just a regular CAT I) there is usually an ILS Hold line painted on the taxiway well before the end of the adjacent ILS runway, is there one associated with the ILS you were flying? Was there traffic waiting to depart at the end of the runway? Just some other causes of a moving ILS needle that the airplane may try to follow.  

Does it wallow on all ILS approaches?

[Yetti]

Mine is as good as the guy holding the yoke.

[Hank]

10 minutes ago, Yetti said:

Mine is as good as the guy holding the yoke.

Sorry about that! My Brittain units are much better than me . . .