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Final Approach
I am trying to understand a feature of the Sandel 3308 that is only documented in a couple of places, and not very clearly as far as I can tell, which may be because the details are probably somewhat installation-dependent.
As documented, with Auto Slew set to on, the Sandel course pointer automatically rotates to the desired course direction in response to a signal sent by the "nav receiver", which is normally a GPS. As documented (again), this seems to be mostly of use when flying GPS approaches. This is a great convenience as you don't have to carefully note the desired course and manually twist the OBS knob. There is no documentation that I can find about whether auto slew works with VLOC-based approaches, and it definitely doesn't work with VOR approaches. However, I noticed long ago that it DOES indeed work with ILS and LOC (including LOC BC) approaches. It makes sense that it COULD do this once the inbound FAC is the current leg, since the GPS database contains information about the courses of most if not all published legs of the approach, and even displays them when the active flight plan is viewed in XPNDed mode. (However, this begs the question of why it doesn't work with VOR approaches.)
I could have sworn that this use was documented in the Sandel pilot's guide, but it is not (unless I've missed it). Like a fool I have been using this feature and relying on it. Well today I got bit. I was shooting approaches first at DET then at PTK, and picked up my clearance to PTK on the miss. I was first RV'd north then west and only punched in my flight plan once I was generally east of PTK. This I did using Direct - KPTK - Dest, dialed in the ILS 9R, EXEC'd the modified plan, switched the CDI output from GPS to NAV, and ID'd the localizer. I was very close to the FAC and was vectored north toward it, and only turned to join it when very close. It was extremely bright in the clag and my Sandel was a little dim; I fiddled a bit and made sure the brightness was up all the way. Then I noticed something strange. According to the display on the MFD, I was north of the localizer. The CDI showed that I was left of course, confirming (to me) that I had crossed it. So I turned to re-intercept it, only to find the CDI moving the wrong way. What was going on? I quickly checked the localizer ID and that the HSI was receiving the VLOC signal. Of course the problem was that the course pointer was still on a westbound heading (the display was dim enough that it wasn't obvious which end was the pointer) and auto slew was not working. I recovered quickly, manually turned the OBS and intercepted the localizer, but not before ATC called me up and asked if I was having trouble finding it.
So I'm hoping someone here knows more about this feature. This could have been a simple procedural error on my part. One possibility is that I switched the CDI output to NAV too early, before the inbound approach course was the current leg. But I have the feeling that I may have been using and even relying on an undocumented and thus unreliable feature.
As documented, with Auto Slew set to on, the Sandel course pointer automatically rotates to the desired course direction in response to a signal sent by the "nav receiver", which is normally a GPS. As documented (again), this seems to be mostly of use when flying GPS approaches. This is a great convenience as you don't have to carefully note the desired course and manually twist the OBS knob. There is no documentation that I can find about whether auto slew works with VLOC-based approaches, and it definitely doesn't work with VOR approaches. However, I noticed long ago that it DOES indeed work with ILS and LOC (including LOC BC) approaches. It makes sense that it COULD do this once the inbound FAC is the current leg, since the GPS database contains information about the courses of most if not all published legs of the approach, and even displays them when the active flight plan is viewed in XPNDed mode. (However, this begs the question of why it doesn't work with VOR approaches.)
I could have sworn that this use was documented in the Sandel pilot's guide, but it is not (unless I've missed it). Like a fool I have been using this feature and relying on it. Well today I got bit. I was shooting approaches first at DET then at PTK, and picked up my clearance to PTK on the miss. I was first RV'd north then west and only punched in my flight plan once I was generally east of PTK. This I did using Direct - KPTK - Dest, dialed in the ILS 9R, EXEC'd the modified plan, switched the CDI output from GPS to NAV, and ID'd the localizer. I was very close to the FAC and was vectored north toward it, and only turned to join it when very close. It was extremely bright in the clag and my Sandel was a little dim; I fiddled a bit and made sure the brightness was up all the way. Then I noticed something strange. According to the display on the MFD, I was north of the localizer. The CDI showed that I was left of course, confirming (to me) that I had crossed it. So I turned to re-intercept it, only to find the CDI moving the wrong way. What was going on? I quickly checked the localizer ID and that the HSI was receiving the VLOC signal. Of course the problem was that the course pointer was still on a westbound heading (the display was dim enough that it wasn't obvious which end was the pointer) and auto slew was not working. I recovered quickly, manually turned the OBS and intercepted the localizer, but not before ATC called me up and asked if I was having trouble finding it.
So I'm hoping someone here knows more about this feature. This could have been a simple procedural error on my part. One possibility is that I switched the CDI output to NAV too early, before the inbound approach course was the current leg. But I have the feeling that I may have been using and even relying on an undocumented and thus unreliable feature.
