G5 and Century III (Piper Altimatic IIIC)
- Thread starter jbrrapa
- Start date
thito01
Pre-takeoff checklist
With my Sandel E-HSI, I put it in Loc Norm. It increases the sensitivity per the manual.
I keep mine in heading. Have never tried Loc Norm except when using the ILS.
When you keep the Century in heading mode, does the GPS glidepath automatically couple to the Century at glidepath interercept?
Nope. I guess I should try an RNAV in Loc Norm mode and see if it works. My glideslope coupler is a bit finicky so might have to test it a few times.
thito01
Pre-takeoff checklist
AFAIK, my aircraft does not have a Glide Slope coupler. When I look at the manual, it seems to indicate that the only indication on the panel that one is installed is a "GS Coupled" light, which I don't have (that I know of as it may be incorporated into the Sandel EHSI). This discussion got me to thinking, do I have one and not know it? Is there a simple way to know if one is installed? The controller only has 'Century III'.
Pic here:
http://dinomasters.com/n4306f/IMAG0009.jpg
Tony T.
Pic here:
http://dinomasters.com/n4306f/IMAG0009.jpg
Tony T.
Logbook might tell you. Mine has a light and then I found the box behind the panel where the glovebox originally was.
thito01
Pre-takeoff checklist
Looking at the 337s, I did find a reference to "removed 1C388M and installed IC388-2 Radio Coupler'. Going though the logbooks will take a while. What does the box look like?
Tony T.
Tony T.
AA5Bman
Line Up and Wait
- Joined
- Jun 14, 2009
- Messages
- 822
- Display Name
Display name:
He who ironically no longer flies an AA5B
I'm a little surprised that it works the way you have described it at all. I have a GI275 and Century II which should be the same conceptually, and I don't think mine would work at all in LOC mode to track a GPS course or RNAV approach. Anytime I'm tracking a GPS course with GPSS selected on the GI275, it has to be in heading mode. LOC, OMNI or NAV only work when tracking a CDI course driven by a VOR, at least for me.
When I track a GPS approach with GPS steering on the G5, if the Century AP is in heading mode the AP does not couple onto the GPS glidepath but does couple onto the lateral gudance. If the AP is in loc norm mode on a GPS approach, the AP couples onto the GPS glidepath but does not couple onto the lateral gudance.
AA5Bman
Line Up and Wait
- Joined
- Jun 14, 2009
- Messages
- 822
- Display Name
Display name:
He who ironically no longer flies an AA5B
@jbrrapa It sounds like something is not set up right. Unless there's some reason the AP can't track an RNAV glideslope, I think that's where I'd focus my attention - everything that I have ever read or encountered about the Century is that to get GPSS steering (lateral), that you have to be in heading mode (and I did put a fair amount of research into this when I redid my panel and added all this functionality). This appears to be confirmed true by your post above, at least in terms of the lateral guidance (i.e. that it works in heading mode but not LOC mode to get lateral guidance on a GPS course). Why your AP only couples to a localizer glideslope... dunno. But I think figuring out how to get that to couple to a RNAV glideslope is where I'd focus my attention, not on getting the AP to track a GPS course in LOC mode because I think that part is set up correctly.
My understanding is the AP won't energize the glideslope coupler in any mode except Loc Norm. So having the AP in heading mode for GPSS isn't going to work. But I'm no autopilot expert.
Ryan F.
Cleared for Takeoff
- Joined
- Dec 23, 2016
- Messages
- 1,351
- Display Name
Display name:
Ryan Ferguson 1974
I have an Altimatic III with dual G5s. I can confirm the following...
- If you don't have a glideslope coupler (you'll definitely know if you have one, so if you're not sure, you don't) you will always want to fly RNAV approaches in HDG mode on the autopilot with GPSS enabled.
- If you do have a glideslope coupler, you "may" want to switch the LOC NORM so that the AP will capture both the lateral course and glideslope. There's a caveat to this however.
- Otherwise, just about the only time you'll ever need -- or, at the very least, want -- to use anything other than HDG / GPSS is for an ILS, localizer or localizer back course approach.
The caveat to LOC NORM is that you're utilizing the autopilot in its full analog mode so you'll need to use the heading bug for wind correction, if necessary. You'll also be treated to the full analog experience which means the autopilot will not track as precisely as it would in HDG/GPSS. However, if the autopilot is in reasonably good spec, it will do pretty well. It just won't be as precise as GPSS.
Having recently had my Altimatic III overhauled and a glideslope coupler installed (this was a pretty extensive/expensive ordeal, by the way) when my second G5 was added, I have a couple of thoughts on this.
- If you don't have a glideslope coupler (you'll definitely know if you have one, so if you're not sure, you don't) you will always want to fly RNAV approaches in HDG mode on the autopilot with GPSS enabled.
- If you do have a glideslope coupler, you "may" want to switch the LOC NORM so that the AP will capture both the lateral course and glideslope. There's a caveat to this however.
- Otherwise, just about the only time you'll ever need -- or, at the very least, want -- to use anything other than HDG / GPSS is for an ILS, localizer or localizer back course approach.
The caveat to LOC NORM is that you're utilizing the autopilot in its full analog mode so you'll need to use the heading bug for wind correction, if necessary. You'll also be treated to the full analog experience which means the autopilot will not track as precisely as it would in HDG/GPSS. However, if the autopilot is in reasonably good spec, it will do pretty well. It just won't be as precise as GPSS.
Having recently had my Altimatic III overhauled and a glideslope coupler installed (this was a pretty extensive/expensive ordeal, by the way) when my second G5 was added, I have a couple of thoughts on this.
- Properly installed, the glideslope coupler can be a pretty nice addition to the Altimatic III. Particularly on long flights with approaches to at or near minimums, the GS coupler can mitigate the effects of fatigue on pilot performance.
- Remember, these are really old components. The GS coupler needs to see the AP in "LOC NORM" along with a full scale deflection GS Up signal for 20 seconds prior to capturing the glideslope. This has turned out to be a rather significant consideration because you will find very often you may be vectored onto approaches without enough time for the GS logic to work. Further, you might be taking advantage of HDG/GPSS mode for segments which will allow you to arrive at the GS capture altitude smoothly via VNAV. For these reasons, I don't tend to actually use the GS coupler very much.
- You may also be subject to configuration limitations. In my case I'm restricted to Flaps 15 (rather than 27, which is full flaps) and the pilot's guide recommends that gear be lower right as the glideslope is captured. For my particular aircraft (PA-30) this can present some extra challenges to smoothly flying an approach.
- The big discovery I made was that pitch mode works nearly as well for managing the vertical profile whether it's a VPATH, an LPV approach or an ILS. And if you use PITCH, there's no reason to use LOC NORM for anything other than an ILS or localizer approach, which makes for a nicer approach with no restrictions on GS logic or aircraft configuration.
- Would I go with the GS coupler again? I think so, mainly thinking about issues such as dealing with problems on the aircraft, maybe medical with one of my pax/family members, etc. The AP can be trusted to fly a completely serviceable ILS or, if the logic works, LPV approach. That is very nice functionality to have for a serious IFR machine.
Last edited:
Thanks for your detailed and thouhgtful response.
I have a factory installed glideslope coupler (with green indicator light) with my IIIC. The problem is if I fly a GPS or ILS approach in heading mode with GPSS on, the AP will follow the lateral guidance but will not engage the glideslope coupler. If I fly the same approach in Loc Norm mode with GPSS off, the glideslope coupler will engage but the AP will not follow lateral guidance. Furthermore, the AP will not follow lateral guidance in NAV mode or OMNI mode with or without GPSS.
Ryan F.
Cleared for Takeoff
- Joined
- Dec 23, 2016
- Messages
- 1,351
- Display Name
Display name:
Ryan Ferguson 1974
Got it.
This is the correct behavior and the programmed logic of the unit. The autopilot will only search for vertical guidance to couple to when in LOC NORM mode. This is why you'd need to fly an LPV approach in "LOC NORM" if you wanted the glideslope coupler to engage.
Is the autopilot set up correctly? ROLL, HDG, ALT and PITCH must all be engaged; the radio coupler must be set to LOC NORM; and you must have the heading bug set to the inbound course or near it (in the case of wind correction, the heading bug "helps" the autopilot with the correction.) If this is being done as stated then you may have an issue with your autopilot.
Sounds like a problem with the autopilot. By the way, GPSS on or off won't have any effect on operation if you're not in HDG mode on the autopilot.
Last edited:
If you have a glide slope coupler and when using GPSS and have the approach loaded, once established on the localizer, (the auto pilot should be in ALT mode, all four switches enabled), and then switch from Heading to Loc Norm mode. The Century III will take at least 20 seconds to couple the glide slope. When the Glide Slope Coupler light comes on, the autopilot WILL fly the glide slope. The same is true if you have WAAS on a RNAV WAAS approach. Once established, switch from Heading to Loc Norm mode and when the Glide Slope Coupler light comes on, it will fly the glide slope.
Mongoose Aviator
Line Up and Wait
The heading bug is not for the Altimatic IIIC. Earlier models used the heading bug, but not the IIIC. I think although am not positive that the Century III is very similar to the Altimatic IIIC.
@Bob Ash - Totally Agree. I find operations exactly as you describe with my Altimatic IIIC. Although implied in your post, the glide slope must be intercepted from below which would be normal for a stabilized approach. As you say, there is a minimum 20 second requirement to allow the GS coupler to arm. I plan a minimum of 30 seconds AND 2 nm. (The 2 nm are easier to see where I am then figuring the time and if I blow through 2 nm in less than 30 seconds than I have far bigger problems.) If ATC vectors me too close in to the FAF then I will miss that minimum time requirement and the GS will not couple.
At the FAF during glideslope intercept, I have power reduced and watch for the GS Coupler green indicator light as well as for the aircraft to nose down and follow the glideslope. This thing is so old that I never trust it until I see it happening. Then I still don't trust it but let it do its thing as long as it keeps looking reasonable. It is almost a surprise still every time it works.
And as Bob says, I do not switch over to LOC NORM until established on the approach course (and see lateral guidance on my CDI) and this works for both RNAV and ILS.
Also as Bob says, all four switches must be enabled and LOC NORM must be in place for minimum 20 seconds prior to glideslope intercept. Flipping a switch or turning the dial resets the 20 second minimum timer.
@jbrrapa - Can you post a picture of your Autopilot as well as what year and aircraft it is installed on? There are some differences from one model to another model as referenced in the thread. Exactly which one you have may make a difference in your operation.
Have you tried GPS/RNAV (LPV or LNAV/VNAV) or ILS initially in HDG mode with GPSS on. When established on approach and when you have lateral guidance on CDI, leave GPSS enabled (regardless of whether RNAV or ILS) and now switch to LOC NORM. This should track laterally and when you intercept glideslope then the GS should couple, green light should go on and aircraft should now be continuing to track laterally as well as now tracking glideslope vertically.
Last edited:
I have a 1978 Lance (PA32RT-300T) with Aspen E5, Garmin 530W and Century III Autopilot (the same as an Altimatic IIIC). ILS or RNAV WAAS works exactly the same. On the Garmin 530W I have the approach selected, autopilot engaged (all four buttons engaged) and in Heading mode. On the Aspen E5 it is in GPSS mode (should be the same for the Garmin G5). Once established on the localizer, switch from Heading to Loc Norm (the autopilot needs 20 to 30 seconds to couple to the glide slope), I slow the aircraft to 110 knots and at Glide Slope Intercept, I drop the gear and add 10 degrees of flaps. This will slow the aircraft to 90 knots and fly the glide slope right to the ground if I let it.