Folks,
we had a discussion here about the correct way to intercept and capture an ILS on the STEC 55x, as the manual is not very clear on this. As I am still not IR rated again I have not had a chance to play with this but some of my pilots appear unsure of the correct procedure to intercept an ILS with this AP. As I know that some of you have flown with it or still do, maybe you can help me here to clarify how it’s done correctly.
As far as I understand the manual, the procedure is like this:
- On intercept course to the LOC press the NAV button once to arm NAV/APR mode (NOT the APR button).
- The AP should display NAV/APR and ALT at this stage. AP determines by itself it is tracking a LOC? (How?)
- Once established on LOC, the GS will only arm if you are in ALT hold, loc is established and you intercept from full deflection below.
I am particularly interested in the function of the NAV and APR buttons on the AP controller. The way I understand it, the mode the 55x uses to track a localizer both in LOC only or ILS approaches is the NAV mode, with the APR mode only serving (lateral) to make the tolerance smaller for the CDI deflection. The other thing the APR mode does is arm or disarm GS mode.
What does NOT work imho is to just press the APR button to arm both loc and GS.
The manual is very badly written IMHO in that section as it refers to other sections and back instead of step by step declaring how to do it.
Am I correct in this or how does it work in your experience?
I am told that the S-TEC 55x installed in Cirrus airplanes has different functions, which adds to the confusion. That is why I’d primarily like to hear from non-cirrus operators.
In my old TB10, the procedure was this:
APPR and NAV do pretty much the same thing horizontally – APPR is just a bit more aggressive. Enroute I always used GPSS, but many people use APPR mode instead of NAV.
You’re right, the manual is atrocious.
jwoolard wrote:
Once on an intercept heading, press APPR and HDG together to arm approach mode and keep the current heading
That exactly is my quesiton, does that work?
The manual sais: Intercept the Localizer using the LOC procedure which is to use the NAV mode and that in that case the AP will know by itself that it has to arm NAV/APR as a localizer is tuned.
Some of my pilots said that APR / HDG to intecept did not work for them and I wonder whether that is why.
Mooney_Driver wrote:
does that work?
Well, it did for me! I had an Aspen taking data from a GTN650 over ARINC and passing it on to the autopilot using analogue signals via an ACU2.
I’m pretty sure mine had no way of knowing if it was on a localizer. I guess it could tell if it was on an ILS because the ILS valid signal is present.
The STEC is a relatively straightforward autopilot. The buttons pretty much do what you think they should.
Mooney_Driver,
What didn’t work, the AP didn’t capture the localiser, the glideslope, or both?
In the STEC if you’re not established and in approach mode a good 3nm before glideslope intercept, it won’t descend. On the STEC55 that can be solved by pushing the Alt button until ‘GS’ is displayed, but that needs to be done before GS intercept.
denopa wrote:
What didn’t work, the AP didn’t capture the localiser, the glideslope, or both?
Primarily they were talking about loc intercept. The manual sais, you have to use the NAV button for that.
The manual is very badly written there. The description of an ILS approach is as follows:
Execute a straight-in intercept and tracking of a FRONT-INBOUND LOC course (reference section 3.3.3) while holding the approach altitude. NAV-APR and ALT announciations will appear… (Page 3.13)
Section 3.3.3 reads like this with regards to which button to press.
Press the NAV mode selector switch to engage the Navigation – Approach mode. (Page 3.22)
So this would imply that you need to use the NAV mode selector. Funnily, vor a VOR approach it prescribes the APR selector.
As I said, I’d love to try it out but it will be a while before I can.
I have used the STEC55X for 8 years now and done many approaches with it. i wait until I’m told which approach it is, I then load it on the GNS430W. Around this time, usually, I get vectored to final and given a HDG. At this point the autopilot put on HDG to follow the HDG assigned. As I get nearer I activate the approach on the 430, this draws a magenta line of the final approach track on the Map. I stay on the HDG bug as I’m vectored round towards the inbound track. I change now from GPS to VLOC (if an ILS for example) having checked the ILS frequency on the 430. I’m now set to intercept the inbound track which is the point of the question here and usually ATC has cleared me for the procedure by now and allowing me to intercept.
I press ALL 3 buttons on the STEC55X so that HDG NAV and APR are showing. As the aircraft approaches the inbound track still on the HDG bug, it then goes to NAV for a short time intercepting and finally APR as it intercept properly. Works every time for me.
STOLman wrote:
I press ALL 3 buttons on the STEC55X so that HDG NAV and APR are showing. As the aircraft approaches the inbound track still on the HDG bug, it then goes to NAV for a short time intercepting and finally APR as it intercept properly. Works every time for me.
Now that is the kind of information I was looking for. And it makes a lot of sense too.
Very useful. Thanks. I shall try this routine on mine.
