Coupled ILS Approaches

I’ve had my SR22 for a little more than three months and have been flying quite a bit (130+ on the Hobbs). Most of my approach clearances have been “visual” and as result it’s been a while since I’ve needed to fly an ILS. Recently, during a vectored approach to final, I tried to couple the 55X to the ILS and was unable to intercept the glideslope. I’m not sure if I set everything up correctly. When I filed, I programmed the 430 from departure to destination. Once airborne I went to HDG/VS during the radar vector climb and, when able, I went to NAV GPSS/ALT to allow the 430 to fly the route at altitude. Approaching my destination I selected PROC, entered the approach (let’s say the ILS 18) and “loaded” waiting for my clearance. I then toggled the localizer frequency on both 430’s (verified the IDs) and waited for my clearance. When I was given radar vectors to the ILS 18 approach, I selected PROC and entered “Activate Approach to Vectors.” I then used HDG and VS/ALT as appropriate as I was vectored to the approach. As I intercepted the localizer both 430’s automatically went to VLOC. The aircraft continued to track the localizer, but I never got a GS indication and when the glideslope bar centered, the aircraft remained at the fixed altitude. I disconnected the 55X and hand flew the approach. I’ve gone over the 55X POH (page 37) which says “to arm the GS capture function…the autopilot must be in NAV/APR/ALT modes.” If I’m being vectored to final, using HDG/ALT, how do I get to this mode? Step by step help appreciated.

Bob Mihocik

There are probably multiple ways handle the vectors to final, but here is one. Since I’m not in the plane, doing this from memory, but I’m 98% sure I’ve got all the steps.

  1. Load the approach

  2. Acitivate the approach as Vectors to Final; swap the VLOC freq to active

  3. Fly the vector with the heading bug on the AP. Autopilot on HDG.

  4. Then press HDG and NAV simultaneously (or press and hold HDG + NAV, press NAV again while holding HDG in for GPSS). The autopilot will fly HDG to intercept final approach course. Set ALT hold if not already on.

  5. At intercept, the autopilot will transition to the inbound heading, the HDG light will go out, and NAV will remain on. Now tracking the GPS inbound.

  6. At FAF, Garmin will swap from GPS to VLOC automatically and the autopilot will swap to APR and GS.

Thats it - I think. Really extremely easy. If the autopilot refuses to couple to the GS, hit ALT once more. Usually happens if high at FAF.

Hope the above is helpful.

I second this request for guidance. I feel comfortable with everything else in the (pre-Avidyne) Cirrus instrumentation, but I’ve never succeeded in using the autopilot to fly a fully coupled ILS. It’s probably been good for me, for practice in hand-flying ILS’s, but I would be grateful for any step-by-step or clues about what the missing ingredient is. JIm F

I spent last week-end practicing coupled approaches to Palomar Carlsbad and Long Beach. I always had to hit the ALT once to get the GS. Once established it tracked the approach very nicely. Doing the LOC D at Gillespie the airplane wandered and did not seem to track well. I am going to practice these some more keep better notes and stay off the controls during the approach and VFR conditions.

Here’s how to fly the coupled approach using vectors to final.

  1. Load the approach with the #1 430
  2. When you begin vectors activate the approach (this is when you are given your first heading with the note “vectors final approach course”). Also be sure you have put the LOC freq in the active box and are in VLOC mode at this time.
  3. Fly with the heading bug and the HDG button on the autopilot.
  4. When you get close to intercept (here’s where the ARNAV, 430 and Sandel are very handy) push the HDG and NAV buttons simultaneously. I tend to do this at the last minute when the controller gives the final intercept heading (e.g. turn right heading 350, intercept the 32 localizer, maintian etc.etc.). At this point the autopilot will show HDG, NAV and APR annunciations (the APR annunciator is automatic with a localizer in the NAV mode). The autopilot will intercept the localizer, the heading light will go out and the aircraft will track inbound.
  5. Glideslope capture will occur automatically if and only if;
    a) you’re capturing the glideslope from below (that is the glideslope is above you and you fly into it), and b) the aircraft is in altitude hold mode. There are parameters in the autopilot manual that explain that you have to be at least 60% below the glideslope for at least 10 seconds for the automatic capture to occur. Assuming that is the case you will see the ALT and GS lights annunciated. When glideslope capture occurs then the ALT light will go out and the glideslope will be tracked.
    I suspect that what’s happening with you is that you’re descending as you intercept the glideslope and under that circumstance auto capture will not occur (you can capture that way by hitting ALT twice at the time the GS centers but it’s not automatic). This problem occurs when for example you’re being vectored at 3,000 feet and the OM altitude is say 2500. The controller may say something like turn left 350 to intercept, 3 from marker, maintain 2500 until established on the localizer, cleared for the approach. What many people do is descend to 2500 during the intercept. It’s better to maintain the 3000 in ALT mode, capture the glideslope and track it down. It’s OK to do that and makes capture much easier.
    Hope I covered that all and that it helps.
    Jerry Seckler


It has been my experience that the most common problem of not getting the magic GS light to come on has to do with the following:

The STEC55 really loves to to intercept the ILS from far below. Every time I have interecepted the ILS with full deflection UP, I eventually get the GS light after intercepting the glideslope.

If the deflection is less than full up when I first lock onto the ILS, its a tossup whether I get the GS light or not on glideslope intercept.



Thanks to your help (especially Jerry Seckler and Bob Price) I found the answer! I finally got out last night (nothing like shooting approaches CAVU / No Moon) and confirmed what it takes to couple on a vectored to final ILS - pressing the NAV and HDG buttons simultaneously while in ALT. Bingo! It works!

FWIW (and maybe someone will get some value from this) I added this as Step 8 on my Instrument Approach Checklist kneeboard card (a long time ago…in my Navy flying days…we created kneeboard cards for everything). If someone wants a downloaded version (Word or Excel) or has questions/comments send me an email at

Instrument Approach Checklist

  1. Radios: #1 w/ ATC #2 w/ ATIS & Tower
    —Get Wx / Winds / Altimeter / Rwy
  2. Select Approach [PROC] Select [ENT] Procedure & Transition
    —“Load” or “Activate” If Cleared for Approach
  3. Activate Approach or Vectors To Final
    —[PROC] Cursor Select [ENT]
  4. Confirm VLOC Frequency in Standby
    —Toggle < V > to Active Verify ID
  5. Descend Checklist – Altimeter / Fuel / Mixture / Flaps / Brakes
    —20" Descend @ 140+ 17" Level @ 120
  6. Review Approach Plate Review Missed Approach
    —Verify FPL Sequence
  7. IAF - Time / Turn / Twist / Throttle / Talk
    —If Hold [OBS] Prior to IAF
    —If Activate Specific Leg [FPL] Cursor Select --D-> --D-> [ENT]
    —If Procedure Turn HSI / CDI - GPS or VLOC (As Needed)
  8. For Coupled ILS - If Vectored to Final
    —Fly w/ HDG & ALT or VS then HDG/NAV together w/ ALT
  9. Fly Approach @ 110 w/ 50% Flaps
    —ILS - 13" 500 FPM Non Prec - 10" 1000 FPM
    —Belts / Mixture / Boost Pump / Brakes / Flaps / Lights / Autopilot
  11. FAF - ILS / LOC - Verify CDI VLOC < C > Call
    #2 CDI Set GPS for B/U Verify DH / MDA
  12. If Missed Approach
    —Power / Attitude / OBS / Flaps / Fly A/C / CDI HSI Set GPS
  13. Next Dest / Approach [PROC] For Same Dest
    —If Programmed [FPL] Page 2 [MENU] Activate
    —If New Dest --D-> Identify [ENT] [ENT]

Bob Mihocik / N762CD
Westlake, OH

I have had to press ALT a second time at intercept to get the “GS” indicator to illuminate and have the airplane start down the glideslope.


This is why you must receive proper instruction in using this equipment. I have been flying coupled approaches for 2 years now in Both a New Piper PA32R and Cirrus. The 430’s are great but without proper instruction on how to use the autopilot you will end up like some others…

  1. The auto pilot needs to be in ALT/ APP/ GS mode when established on the final course.
  2. If you are at the correct altitude prior to reaching the FAF then the Glideslope bar should indicate that the GS is above you.
  3. As you approach the FAF the BAR will come down and GS Capture will occur at approx 1 dot abot.

The airplane will fly the coupled approach and will take you the the Touch down zone with nothing more than minor power adjustments…

Go back to school to learn the correct techniques…



Many thanks. Your post explains why I routinely have to push ALT twice to capture and switch to “GS” mode. I can’t wait to try it using your (i.e., “the proper”) technique.


I’ve flown lots of coupled approaches, and only once have I had to manually arm the glideslope function (due to a bum vector.)

The key is that the S-Tec 55 will not arm GS capture unless a list of stuff is true (APR/ALT mode, etc.) but the kicker is that the GS needle has to be at least 40% deflected up (you have to be below glideslope, as you should be on the intermediate leg before the FAF) or it won’t fly it for you. Sensible safety measure, unless you suddenly find yourself behind the plane in IMC because the avionics aren’t doing what you expect! (I had this happen to me in a Baron, once again with a bum vector, but luckily my evil instructor was present; she just laughed at me as I scrambled and started sweating bullets.)

Thanks for the Checklist!

It would be really if everyone would share check lists, helpful hints etc with other members. Even better if they could be posted in the Stuff or other appropriate section of COPA.

Bob 96SY

Kind of off the theme of the original thread, but I am going into CRQ tomorrow and I noticed that AP couple approaches NA 960 MSL. I am probably getting there after the layer lifts, and usually hand-fly ILS’s anyway, but why this notation?

I don’t know about THAT particular one, but usually it means the ILS gets a “little wiggly” due to terrain, buildings or other things that cause some reflection or irregularities of the signal. That same notation is on one I do fly and that is the ILS into Monterey Ca. Now what I can’t say is why they do that for sure. I suspect they think the automation will over react.

KLVK ILS 25 has a similar NA at 1400’, I think. I fly it lots fully coupled (VFR) and smooth as silk with 55x and DFC100… So who knows what makes them get funky!

From an FAA designer on a public forum:


After we design the procedure, flight inspection will take it for a spin. Generally this note is added after flight inspection has found some anomoly. Then we will add the note to the procedure. Here is criteria proof (from the 8260.19D).

(d) When the rate of reversal in the GS exceeds the tolerances of Order 8200.1, United States Standard Flight Inspection Manual, chapter 15, establish a restriction for autopilot coupled approach 50 ft above the point (MSL) where the out-of-tolerance condition exists. Use:“Chart note: Autopilot coupled approach NA below 540.”


Because of the topgraphy of the airport, the glideslope is unreliable that close to the runway and there is rising terrain underneath the final approach course… The runway is a modest version of a ski jump – just like those aircraft carrier ramps for the Harrier jump jet – the runway dips slightly in the middle and then rises up noticeably. Also, the terrain drops away under the glidepath with the controlling obstacle at 731’ and the last mile or so is below the runway elevation.


Another advantage of WAAS LPV approaches. I had not realized how “choppy” ILS’s are until I started doing LPV’s. I realized that it takes less maneuvering to stay on a LPV than an ILS, which made me realize it was the ILS, not just the “flying” part, that was scalloped!

I’ve noticed that also, first time someone has mentioned it

Thanks for all the response, it was helpful. Made it into CRQ with just a patchy layer on the ILS-24 mostly VMC with no issues. However the en-route portion was a real challenge, 2.3 hours of solid IMC from Southern Utah to San Bernardino, with embedded thunderstorms. I was sure happy to have active radar. Since when does SoCal have thunderstorms? Nice to see a clean radar screen in Threat ID position (TIP), when the NexRad was so ugly. I would not have made this trip with just NexRad. I navigated around any precipitation that showed up at my altitude or higher on active radar even if it were green due to concern of building cumulus. I tried to get a Western vector around the area, but the Military seems to own that area, and ATC could not get permission to pass me through the restricted areas, so I had to skirt the western edge of that large convective Sigmet. Was a pretty smooth trip with only some occasional light rime.