Maybe I’m crazy. In dealing with the people at S-Tec and my local avionics tech, as we try to get to the bottom of why my autopilot is suddenly off track, a conflict of opinion has arisen.
My contention is that in the nav mode on the S-Tec 55x (would be the same as the 55), non GPSS mode and not in the OBS mode on the Garmin, the yellow heading selector direction does not influence the CDI and therefore the autopilot. In other words, the course is set by the GPS inputs, not the heading selector, Am I correct?
If while in the NAV mode you have VLOC selected in the Garmin, the HSI acts off the VOR freq or ILS/LOC freq you have selected without any input from the GPS. If you’re tracking a VOR just keep adjusting the CDI needle to keep the bar from being deflected(crab for the wind etc).
You don’t adjust the CDI needle. Do you mean you fly the airplane to keep the needle centered ?
The autopilot flies the HSI.
No, it follows the needle from the GPS or VLOC receiver. You just happen to see a needle on the HSI.
If you have GPS mode selected in the Garmin, the HSI will treat the course laid out by the GPS as if were direct to a waypoint,
The HSI is too dumb to treat anything. It’s just a display, Sandel or steam gauge.
however you have to manually turn the CDI heading to the appropriate Direct Track (DTK) heading.
Desired Track. They’re not headings, they are courses / tracks, which is an important distinction when discussing autopilots. Courses are ahead of you and track is behind you in spite of the “DTK” nomenclature, but that’s being nitpicky
Once the CDI needle is on the DTK you don’t need to adjust the HSI again as it will track the direct course laid out by the GPS much like it tracks the LOC in VLOC mode.
So I think the answer is no.
??? We’re not even sure what the original poster is asking. Does his term “heading selector” mean heading bug or course pointer ?
When you want to track the GPS course on the S-Tec 55 in the NAV mode, you have to set the CDI needle to the DTK you want to fly as indicated by the Garmin, it will tell you when to turn the needle. Once you set it, leave it alone until you reach the next waypoint.
This is my understanding of how the S-tec 55 works with the autopilot.
??? these are the same
If someone sees a mistake here, please correct me asap.
Like I said, the terminology will get you. You don’t “set a CDI needle” or “manually turn the CDI heading”, but we understand what you’re trying to say even if its explained poorly.
You set a course pointer on an HSI. If that course pointer setting is sent to a VLOC receiver, it can change the needle deviation seen on the HSI and thus seen by the autopilot. If that course pointer setting is sent to a GPS receiver in auto leg mode, it doesn’t change the needle deviation. If that course pointer setting is sent to a GPS receiver in OBS mode, it can change the needle deviation. The autopilot follows the needle when the autopilot is in nav mode and it uses the HSI course pointer to help it do course intercept and wind correction, which is why you should follow the Garmin’s prompt to set the course pointer to the GPS desired course (DTK).
If you’re off course while navigating with GPS (auto leg mode) and you decide to return to course by engaging nav mode on the autopilot, you need to set that HSI course pointer to the GPS desired course (desired track or DTK) to help the autopilot set up a course intercept.