Intercepting an Active Leg
Printed From: Avidyne
Category: Avidyne General
Forum Name: IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM
Forum Description: Topics on Avidyne's IFD 5 Series and IFD 4 Series Touch Screen GPS/NAV/COM
URL: http://forums.avidyne.com/forum_posts.asp?TID=2197
Printed Date: 07 May 2024 at 9:59am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: Intercepting an Active Leg
Posted By: RickHill
Subject: Intercepting an Active Leg
Date Posted: 12 May 2021 at 7:37pm
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I have a 550 paired with Aspen 2000 Pro, and S-Tec autopilot. I've pretty much figured out all the easy stuff, and most of the hard stuff---I hope. So I wanted to simulate a very typical ATC clearance such as fly heading 360 intercept Vxxx on course.
I made the leg I wanted in intercept the active leg, spun the heading bug on the Aspen to 360, allowed the airplane to get established on the heading, and then pressed GPSS. To my surprise, the Avidyne/Aspen/Stec decided that a different heading was appropriate. I was far enough away from the leg to be intercepted so that it was not in some capture mode. It simply turned to its own intercept heading sort of like a Private Pilot. I know that the work-around is to simply stay in heading mode until the CDI comes off the peg, but the behavior---selecting its own intercept---seems unreasonable for a IFR certified navigator.
- I'm pretty sure that the Stec is not at fault; it doesn't pick headings.
- Aspen claims, and I believe them, that in GPSS mode, the navigator is in total charge of the operation.
- Avidyne wants me to speak with my avionics guys and have them speak to support. Before I do that, I thought I'd seek advice here.
Thanks in advance.
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Rick
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Replies:
Posted By: Gring
Date Posted: 12 May 2021 at 9:05pm
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The instruction that you provided is something that I get regularly. When you activate the leg, the magenta line becomes your desired navigation track (DTK) and you have some type of cross track deviation since you are left or right of course by some amount. The question becomes, at what intercept angle does the IFD calculate to intercept the active leg. I don't know the answer to that. However, in practice, I put the autopilot in heading mode since ATC gave you a specific heading to fly (in this case 360), and then arm the GPSS mode (this worked on my 55X with built in GPSS). In an autopilot where GPSS is not integrated, and you have a GPSS module, or in your case GPSS from the Aspen, I don't know what you can do. An alternative, is to use heading mode, and arm the NAV mode on the autopilot (all but the basic STEC autopilots can do this). This will fly the proper intercept course instructed by ATC, and will automatically turn on course once the active leg is intercepted (by switching to NAV mode, or GPSS mode in a 55X).
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Posted By: PA20Pacer
Date Posted: 13 May 2021 at 8:39am
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Hi Rick-
The behavior you describe is what I would expect. Once GPSS is activated, the heading bug setting is ignored in favor of a heading calculated by the navigator to fly the desired flight plan. As you observed, if you wish to fly a leg with the heading selected by the heading bug, the GPSS mode should not be selected.
Regards,
Bob Siegfried, II
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Bob Siegfried, II
Brookeridge Airpark (LL22)
Downers Grove, IL
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Posted By: HenryM
Date Posted: 13 May 2021 at 2:27pm
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I have a simple autopilot, an STEC-30 with GPSS and altitude hold. There's a switch on my panel that selects between HDG and GPS. Whenever I'm flying heading assigned by ATC I stay in HDG mode, and dial the appropriate heading into the DG of my plane. I stay with that until I want to continue following my IFD540 instructions. I'm pretty much with Bob, if you want to fly a heading, stay in HDG mode.
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Posted By: oskrypuch
Date Posted: 15 May 2021 at 2:07pm
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Rick,
Which STEC A/P?The 55x has a HDG -> NAV (or GPSS) intercept mode, works quite nicely.
If that is not available, then what you are seeing, is what you get.
* Orest
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