Bennett Posted July 19, 2012 Report Posted July 19, 2012 I would appreciate some commentary and help here. Been flying IFR approaches (ILS, VOR, VOR-DME, LDA, ADF< Non-Precision GPS overlays, GPS, GPS WAAS (even with "suggested" vertical guidance on some Garmin units), for years, but not yet the new ("almost precision")VPN (LPV) approaches. I was doing just fine until I attended a FAA seminar last night on VPN (LPV)approaches. I guess I may not have been understanding them correctly, or I don't yet understand how to use my equipment in the optimum manner. As I understand it, these approaches are capable of vertical guidance (like an ILS) once past the FAF. Lets take an example. I load the flight plan into the Garmin GTN 750 which includes the chosen VPN approach. (Actually this is quite easy on the GTN 750). After take off, I set the KAP 150 in heading mode with the bug set to take me to the first waypoint of the flight plan. I then engage the Icarus SAM GPSS unit, which as I understand it, converts the GTN 750's digital output to an analog readable by the KAP 150. The aircraft flies the flight plan perfectly, or at least better than I can, and at some point altitude hold is engaged. I am now on the way to the initial approach fix, still with GPSS engaged, and in heading mode on the KAP 150. This combination will fly a hold or procedure turn if it is part of the approach. After the initial approach fix, or inbound towards the FAF, I think I should disengage the GPSS steering, and switch the KAP 150 to approach mode. Questions: Is this the best procedure? Will the KAP 150 track the glideslope to DA? (I have not yet tried this) I have downloaded all the pertinent manuals (GTN 750, Icarus SAM, and KAP 150)and apparently I am missing something here. I'm relatively sure that someone on this forum has the same or similar combinations of avionics, and I sure would appreciate hearing their experiences with VPN (LPV)approaches. Thank you.
fantom Posted July 19, 2012 Report Posted July 19, 2012 The KAP 10 will track the GS well beyond DA, so be careful, Bennett. I have a 530W so can't comment on the 750 GPSS. How many IMC actual, published holds have people been required to fly? Very, very rare in my experience, sort of like back course ILS's.
Bennett Posted July 19, 2012 Author Report Posted July 19, 2012 Fantom, I'm very much aware about the potential dangers of tracking a glideslope past the DA. Same potential problem with an ILS. I really don't have any intention to actually using autopilot tracking below about 700' for a 200'-250' DA. (And I would de-couple the autopilot much higher than that if I were to break out of IMC between 1000' and 2000' - I prefer hand flying the approach in those circumstances, but there are always the potential bad situation in which tracking lower might make sense.) These new VPN (LPV)approaches are quite low, with 250' being the norm, and some down to 200'. At the VPN (LPV)seminar, it was pointed out that you can have a vertical GPS error of 150' before the Garmin units will report loss of vertical guidance - that's scary!. In my previous Mooney I had a KFC 200 autopilot that tracked the ILS beyond what I would be willing to do on a normal approach. Each of these autopilots would be in approach mode for an ILS, (without GPSS steering via the Icarus SAM unit), but I am not sure what is best for a VPN approach. Hence my question.
M016576 Posted July 19, 2012 Report Posted July 19, 2012 Quote: Bennett I would appreciate some commentary and help here. Been flying IFR approaches (ILS, VOR, VOR-DME, LDA, Non-Precision GPS overlays, GPS, GPS WAAS (even with "suggested" vertical guidance on some Garmin units), for years, but not yet the new ("almost precision")VPN approaches. I was doing just fine until I attended a FAA seminar last night on VPN approaches. I guess I may not have been understanding them correctly, or I don't yet understand how to use my equipment in the optimum manner. As I understand it, these approaches are capable of vertical guidance (like an ILS) once past the FAF. Lets take an example. I load the flight plan into the Garmin GTN 750 which includes the chosen VPN approach. (Actually this is quite easy on the GTN 750). After take off, I set the KAP 150 in heading mode with the bug set to take me to the first waypoint of the flight plan. I then engage the Icarus SAM GPSS unit, which as I understand it, converts the GTN 750's digital output to an analog readable by the KAP 150. The aircraft flies the flight plan perfectly, or at least better than I can, and at some point altitude hold is engaged. I am now on the way to the initial approach fix, still with GPSS engaged, and in heading mode on the KAP 150. This combination will fly a hold or procedure turn if it is part of the approach. After the initial approach fix, or inbound towards the FAF, I think I should disengage the GPSS steering, and switch the KAP 150 to approach mode. Questions: Is this the best procedure? Will the KAP 150 track the glideslope to DA? (I have not yet tried this) I have downloaded all the pertinent manuals (GTN 750, Icarus SAM, and KAP 150)and apparently I am missing something here. I'm relatively sure that someone on this forum has the same or similar combinations of avionics, and I sure would appreciate hearing their experiences with VPN approaches. Thank you.
jackn Posted July 19, 2012 Report Posted July 19, 2012 Hi Bennet I have a similar set-up. 430W, Icarus, KFC150. I will disconnect the GPSS Prior to the inbound course or even procedure turn. Since the A/P is already in heading mode, I just use heading bug. Then, I set the inbound course on the HSI, and hit appr mode. A/P will grab it and virtual GS.
Cruiser Posted July 19, 2012 Report Posted July 19, 2012 I believe GPSS is heading information provided by the GPS. The GPS continuously provides computed heading data to the A/P and the heading bug on your HSI is not coupled to the A/P. If you want to use heading info from any other source (than the GPS) then you must disable GPSS steering. IF you are on a GPS approach using the GPS for both lateral and vertical guidance then it really doesn't matter. Good practice and force of habit would be to disable GPSS when on an approach so as to not allow the A/P to continue following heading info from the GPS if a different approach is being used such as ILS or VOR and use the heading bug.
Jeff_S Posted July 19, 2012 Report Posted July 19, 2012 First of all, I've never heard of a "VPN" approach. Did they change the name, or do you mean an "LPV" approach? Or is it something else entirely? I may need an educashun on that one. As to how to fly them, my set-up is different as I have a GNS480 with an S-TEC 55 A/P and GPSS. I would fly the entire approach using GPSS until I'm establshed on the final approach path (outside the FAF). Then I switch the A/P to NAV/APR mode, and that will capture the GS and ride the rails down as far as I let it.
Bennett Posted July 19, 2012 Author Report Posted July 19, 2012 I must be getting dyslectic. The correct terminology is, of course, LPV. We have far too many acronyms for the GPS approaches. Good catch, Jeff. Thank you all for all your replies. The major question I have at this point is whether or not to switch off the Icarus SAM between the IAF and the FAF. Looking at a number of LPV approaches, it would appear that the angular decent (vertical guidance) is sometimes (usually) different between the IAF and the FAF, as opposed to the FAF and the DA. The glideslope may well extend past the IAF outwards, and one could capture that glideslope further out than the IAF, but while the glideslope has some vertical latitude,the IAF is a hard number and cannot be descended below until crossing that fix. A step down to that altitude may be better practice than trying to use the autopilot to follow the FAF/DA glideslope further out. That being the situation, where is the best place to switch off GPSS, and switch to the approach mode on the autopilot (until disengaged at a reasonable altitude)? What puzzles me a bit is the fact that the GTN 750 (like the G1000) puts out a digital signal, while the KAP 150 is set up for an analogue signal. Does the approach setting on the KAP 150 (or KFC 200, for that matter) work better on an analogue basis (Icarus switched off), or maintaining GPSS as a digital signal?
Bennett Posted July 19, 2012 Author Report Posted July 19, 2012 I think Jackn has the most practical answer, and I am sure that this will work. Thank you. I am going to fly a few of these LPV approaches in VFR conditions in the next few weeks (after Oshkosh), using the GPSS steering, or not, as well as the regular approach mode at the FAF, using a step down to the FAF altitude. Three different brands of avionics, with both digital and analogue systems could be a problem, and I want to sort this all out before trying one in actual conditions.
jackn Posted July 19, 2012 Report Posted July 19, 2012 Quote: Bennett I must be getting dyslectic. The correct terminology is, of course, LPV.
Cruiser Posted July 19, 2012 Report Posted July 19, 2012 Bennett, The A/P will not command a descent until the GS needle is "centered" so capturing the GS path outside the FAF works. Remember, there is no GS "signal", it is a GPS calculated data point comparing the planned altitude to the GPS reported altitude. It will follow the approach plan. The GPSS unit converts the digital to analog so the A/P can use it. These old A/Ps were never intended to use GPS data when they were designed. The new all digital A/Ps have roll steering built in.
Bennett Posted July 19, 2012 Author Report Posted July 19, 2012 Quote: Cruiser Bennett, The A/P will not command a descent until the GS needle is "centered" so capturing the GS path outside the FAF works. Remember, there is no GS "signal", it is a GPS calculated data point comparing the planned altitude to the GPS reported altitude. It will follow the approach plan. The GPSS unit converts the digital to analog so the A/P can use it. These old A/Ps were never intended to use GPS data when they were designed. The new all digital A/Ps have roll steering built in.
danb35 Posted July 20, 2012 Report Posted July 20, 2012 As I understand it (and with the caveat that I've never flown with a KAP 150), the glideslope won't arm unless the autopilot is in approach mode, and you can't be in both approach and heading mode at the same time. If that's correct, you'd need to switch from HDG to APP before reaching the FAF. In the GPS approaches I've seen you'd be straight in to the runway by the time you reach the FAF anyway. So, once the needle is centered heading toward the FAF, switch to APP mode.
jlunseth Posted July 20, 2012 Report Posted July 20, 2012 I have flown quite a few LPV's. My setup is similar to yours, 430W, Icarus SAM, and KFC200. You can use the GPSSwith the AP in HDG mode until you are about a half mile outside the FAF. I found that if you wait until the FAF or inside the FAF to switch to APPCH mode, the AP will not always couple to the GS. When you switch to APPCH obviously you will need to have the final approach course dialed in to the HSI, as the AP will no longer be using the GPSS signal for guidance. Be sure to watch the annunciator and make sure that you see GS light up. On the glide slope, be sure to monitor your airspeed and add power if necessary. The AP only knows to pitch up if you fall below the slope, which can be a problem if power is not added in. For whatever reason I have never experienced this during an ILS, but have during LPV's. Also be sure to watch the annunciator and insure that the AP goes from ARMED to CPLD. Can't go into the explanation on this iPad, but if you are very close to the final approach course when you switch to APPCH the AP will not always couple to the approach course. The AP will fly to the DA and lower if you let it. You need to disconnect at or above the DA and hand fly. It is possible, but not recommended, to hit alt. hold to fly the DA. Bear in mind that the GPS will suspend and cease directing the AP when the aircraft arrives at the Missed approach waypoint, usually the runway waypoint. You will need to hand fly the initial missed approach course. In the case of a missed approach proc. that requires a straight ahead climb to an altitude, you should not re-enable the GPS until you have reached that alt. Then you can press CDI on the GPS to re-enable the GPS, also putting the AP in HDG mode and the Icarus in GPSS mode. This will enable the GPS to fly the missed approach including any hold. You will need to handle alt. and power.
Bennett Posted July 23, 2012 Author Report Posted July 23, 2012 "I have flown quite a few LPV's. My setup is similar to yours, 430W, Icarus SAM, and KFC200. You can use the GPSSwith the AP in HDG mode until you are about a half mile outside the FAF. I found that if you wait until the FAF or inside the FAF to switch to AAPCH mode, the AP will not always couple to the GS. When you switch to APPCH obviously you will need to have the final approach course dialed in to the HSI, as the AP will no longer be using the GPSS signal for guidance. Be sure to watch the annunciator and make sure that you see GS light up. On the glide slope, be sure to monitor your airspeed and add power if necessary. The AP only knows to pitch up if you fall below the slope, which can be a problem if power is not added in. For whatever reason I have never experienced this during an ILS, but have during LPV's. Also be sure to watch the annunciator and insure that the AP goes from ARMED to CPLD. Can't go into the explanation on this iPad, but if you are very close to the final approach course when you switch to APPCH the AP will not always couple to the approach course. The AP will fly to the DA and lower if you let it. You need to disconnect at or above the DA and hand fly. It is possible, but not recommended, to hit alt. hold to fly the DA. Bear in mind that the GPS will suspend and cease directing the AP when the aircraft arrives at the Missed approach waypoint, usually the runway waypoint. You will need to hand fly the initial missed approach course. In the case of a missed approach proc. that requires a straight ahead climb to an altitude, you should not re-enable the GPS until you have reached that alt. Then you can press CDI on the GPS to re-enable the GPS, also putting the AP in HDG mode and the Icarus in GPSS mode. This will enable the GPS to fly the missed approach including any hold. You will need to handle alt. and power." . . ................................................................................................................................................................................................ Great advice. Thank you for that information. I will try this out when I return from Oshkosh.
jlunseth Posted July 23, 2012 Report Posted July 23, 2012 I don't have a GTN but I have the manual. I noticed in the manual that not only does the unit suspend at the missed approach waypoint (i.e. "RWY31"), it puts a message up on the screen whether you want to re-enable guidance. I did not find the manual very helpful on just exactly what you should do at this point, but if you take the situation I was talking about earlier, where the missed approach instructions are climb straight ahead to an altitude, then turn to a waypoint, I think I would experiment with just letting that option screen sit there until I get the straight ahead climb to the altitude done. At that point I would elect to re-enable GPS guidance by touching the touch screen button. You will probably need to experiment with that.
flyboy0681 Posted July 28, 2012 Report Posted July 28, 2012 I have an identical setup as Bennett, 750, ICARUS & KAP 150. I'm in the middle of my IR training and haven't flown any coupled approaches yet, but I have spoken to my partner about it, who has flown a few. He says that the KAP has to be in Approach mode because it's taking it's inputs from the HSI and the only way to engage the A/P to track the localizer and glideslope is through approach mode. Since the GPS is feeding the HSI for lateral and vertical guidance, this makes sense. The GPS Steering plays no role in the actual approach except getting you to the final approach course.
Bennett Posted July 28, 2012 Author Report Posted July 28, 2012 Quote: flyboy0681 I have an identical setup as Bennett, 750, ICARUS & KAP 150. I'm in the middle of my IR training and haven't flown any coupled approaches yet, but I have spoken to my partner about it, who has flown a few. He says that the KAP has to be in Approach mode because it's taking it's inputs from the HSI and the only way to engage the A/P to track the localizer and glideslope is through approach mode. Since the GPS is feeding the HSI for lateral and vertical guidance, this makes sense. The GPS Steering plays no role in the actual approach except getting you to the final approach course.
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