AirTalk.org Aviation discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Step Down or Track Glide slope on GPS overlay approach          AirTalk.org Forum Index -> Instrument Flight Rules View previous topic :: View next topic   Author Message Mooney Guest Posted: Sat Apr 14, 2007 6:11 am    Post subject: Step Down or Track Glide slope on GPS overlay approach I have just recently acquired a Garmin 430/WAAS for my Mooney 201. In practicing approaches to familiarize myself with the unit, I went up with an instructor to get some advice/tips. I had flown a GPS overlay approach (NDB/GPS Runway 5 KLWM, Lawrence MA) previously in VFR conditions and tracked the vertical guidance provided by the GPS and loved it ... very stable approach and no need to dive/level/dive etc. Then I went up with the instructor and did what I thought was a great approach (also NDP/GPS 5 KLWM) and he was upset I didn't fly it more like the "original" non-precision approach by identifying fixes with cross radials and doing the stepdowns. So that is the question. Which technique should be used and why? If I give up the "track the GPS glideslope" approach I feel I'm giving up the advantage of a very stable/controlled approach configuration and not sure what I'm gaining in return. Comments from the experts?? Final questions: With the WAAS GPS on this approach, can I descend to the lower minimum based on identifying the final stepdown fix if I am just flying the GPS's vertical guidance? Where are the answers to these questions provided? Back to top Robert M. Gary Guest Posted: Sat Apr 14, 2007 6:11 am    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach On Apr 13, 7:26 pm, "Mooney" <ccorm...@comcast.net> wrote: Quote: I have just recently acquired a Garmin 430/WAAS for my Mooney 201. In practicing approaches to familiarize myself with the unit, I went up with an instructor to get some advice/tips. I had flown a GPS overlay approach (NDB/GPS Runway 5 KLWM, Lawrence MA) previously in VFR conditions and tracked the vertical guidance provided by the GPS and loved it ... very stable approach and no need to dive/level/dive etc. Then I went up with the instructor and did what I thought was a great approach (also NDP/GPS 5 KLWM) and he was upset I didn't fly it more like the "original" non-precision approach by identifying fixes with cross radials and doing the stepdowns. So that is the question. Which technique should be used and why? If I give up the "track the GPS glideslope" approach I feel I'm giving up the advantage of a very stable/controlled approach configuration and not sure what I'm gaining in return. Comments from the experts?? Final questions: With the WAAS GPS on this approach, can I descend to the lower minimum based on identifying the final stepdown fix if I am just flying the GPS's vertical guidance? Where are the answers to these questions provided? There is no reason you need to use the minimum altitude unless the altitude on the plate has a bar abouve it (meaning max altitude) -robert Back to top Viperdoc Guest Posted: Sat Apr 14, 2007 6:11 am    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach I have a 530W/430W combo recently, and in fact did some RNAV/GPS approaches tonight. I find it easier to let the autopilot track the GS in LNAV/VNAV approaches rather than dive and drive. It's identical to an ILS- when the DH is reached, then either land or go around. It's probably the same reason why precision approaches with GS are easier to fly than non precision approaches. By the way, tracking the VNAV or LPV glideslope and GPS "localizer" were much smoother than a traditinional ILS or localizer approach. Back to top Ron Rosenfeld Guest Posted: Sun Apr 15, 2007 4:17 pm    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach On 13 Apr 2007 19:26:50 -0700, "Mooney" <ccormsby (AT) comcast (DOT) net> wrote: Quote: I have just recently acquired a Garmin 430/WAAS for my Mooney 201. In practicing approaches to familiarize myself with the unit, I went up with an instructor to get some advice/tips. I had flown a GPS overlay approach (NDB/GPS Runway 5 KLWM, Lawrence MA) previously in VFR conditions and tracked the vertical guidance provided by the GPS and loved it ... very stable approach and no need to dive/level/dive etc. Then I went up with the instructor and did what I thought was a great approach (also NDP/GPS 5 KLWM) and he was upset I didn't fly it more like the "original" non-precision approach by identifying fixes with cross radials and doing the stepdowns. So that is the question. Which technique should be used and why? If I give up the "track the GPS glideslope" approach I feel I'm giving up the advantage of a very stable/controlled approach configuration and not sure what I'm gaining in return. Use the stabilized approach because, as you have discovered, it is easier to fly! Aren't ILS's easier to fly than dive & drive non-precision approaches? Just don't forget to level off at the MDA. "You" cannot treat MDA as a DA without special authorization. Quote: Comments from the experts?? Final questions: With the WAAS GPS on this approach, can I descend to the lower minimum based on identifying the final stepdown fix if I am just flying the GPS's vertical guidance? The requirement to identify KRIED is not dependent on how you are flying the approach. However, if KRIED is in your DB, you can use the GPS to identify it. Quote: Where are the answers to these questions provided? Which question? The issue of stabilized versus D&D approaches is discussed in airline safety material. Rules for flying approaches are in the FAR's and AIM. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) Back to top Ron Rosenfeld Guest Posted: Sun Apr 15, 2007 4:18 pm    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach On 14 Apr 2007 08:16:05 -0700, "paul kgyy" <phkmn2000 (AT) yahoo (DOT) com> wrote: Quote: Sometimes step-downs are to clear obstacles. I haven't tried the 430W yet, but how does the "stabilized approach" deal with this? Is there a variable glideslope? The GP angle can vary by approach. Not all LNAV approaches will have advisory vertical guidance. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) Back to top Ron Rosenfeld Guest Posted: Sun Apr 15, 2007 4:25 pm    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach On 14 Apr 2007 06:04:57 -0700, "Mooney" <ccormsby (AT) comcast (DOT) net> wrote: Quote: I agree that this is easier to just fly the GPS glideslope and my temptation is to just do it that way, but I'm trying to figure out why my instructor is adamant that I use the stepdown process. You'll have to ask him. It may be due to lack of familiarity with the stabilized approach concept, and its advantages. Quote: Can you be confident if you fly the glideslope that you will not violate the minimum altitudes at each stepdown fix? Yes. However, in the words of a former politician, "Trust, but Verify". Quote: If you are below these BUT ON THE GS are you legal or does the GS have no legal status? The GP does not supercede published minimums. Quote: More importantly is there any safety issue of just flying the GS? I've not seen an approach with advisory vertical guidance that violates a stepdown fix. The GP in these instances is, on Jepp charts, represented by a light dashed line, and a GP angle notation. So, if you are using Jepp charts, you can verify this. The only "issue", and it is not unusual in the NE (ME and NH, at least) is that the marginal WAAS coverage occasionally leads to loss of the WAAS-GP signal. So then you'll be flying without the GP signal. Not a big deal if you're ready for it. And, if you are properly set up, you can still continue down to MDA at the same rate, or perhaps slightly faster. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) Back to top Mooney Guest Posted: Sun Apr 15, 2007 7:02 pm    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach I think what we are saying is that even though Jeppesen says the VNAV GS ensures being above the step-down fixes and GARMIN wrote approved software to make sure the GS needle properly indicates the Jeppesen- provided vertical guidance, the pilot needs to explicitly note whether the step-down fixes have been passed and not follow the GS unless it is consistent with these restrictions. So, it is ok to fly the glideslope, but you must perform these checks as the approach progresses. Seems like a good double check yet lets me keep the stablized approach. The other issues of MDA vs DA and the possible advantage of entering VFR earlier if you dive & drive are noted. Thanks to everyone who responded. Back to top Dave Butler Guest Posted: Sun Apr 15, 2007 8:45 pm    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach Mooney wrote: Quote: I think what we are saying is that even though Jeppesen says the VNAV GS ensures being above the step-down fixes and GARMIN wrote approved software to make sure the GS needle properly indicates the Jeppesen- provided vertical guidance, the pilot needs to explicitly note whether the step-down fixes have been passed and not follow the GS unless it is consistent with these restrictions. So, it is ok to fly the glideslope, but you must perform these checks as the approach progresses. Seems like a good double check yet lets me keep the stablized approach. The other issues of MDA vs DA and the possible advantage of entering VFR earlier if you dive & drive are noted. Thanks to everyone who responded. Google for "constant angle non-precision approach" for lots of discussion about the pros and cons. Dave Back to top scott moore Guest Posted: Mon Apr 16, 2007 8:14 pm    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach Stable controlled descent approaches are both easier and safer than stepdown approaches, which was what the airlines found. There is no reason to expect different from light airplanes. I would find an instructor more amenable to new technologies. Mooney wrote: Quote: I have just recently acquired a Garmin 430/WAAS for my Mooney 201. In practicing approaches to familiarize myself with the unit, I went up with an instructor to get some advice/tips. I had flown a GPS overlay approach (NDB/GPS Runway 5 KLWM, Lawrence MA) previously in VFR conditions and tracked the vertical guidance provided by the GPS and loved it ... very stable approach and no need to dive/level/dive etc. Then I went up with the instructor and did what I thought was a great approach (also NDP/GPS 5 KLWM) and he was upset I didn't fly it more like the "original" non-precision approach by identifying fixes with cross radials and doing the stepdowns. So that is the question. Which technique should be used and why? If I give up the "track the GPS glideslope" approach I feel I'm giving up the advantage of a very stable/controlled approach configuration and not sure what I'm gaining in return. Comments from the experts?? Final questions: With the WAAS GPS on this approach, can I descend to the lower minimum based on identifying the final stepdown fix if I am just flying the GPS's vertical guidance? Where are the answers to these questions provided? Back to top Guest Posted: Sat Apr 28, 2007 5:29 pm    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach On Sun, 15 Apr 2007 07:25:50 -0400, Ron Rosenfeld <ronrosenfeld (AT) nospam (DOT) org> wrote: Quote: I've not seen an approach with advisory vertical guidance that violates a stepdown fix. The GP in these instances is, on Jepp charts, represented by a light dashed line, and a GP angle notation. So, if you are using Jepp charts, you can verify this. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) Ron, are you able to provide us with some examples? Stan Back to top Guest Posted: Sun Apr 29, 2007 6:11 am    Post subject: Re: Step Down or Track Glide slope on GPS overlay approach On Sat, 28 Apr 2007 12:29:12 GMT, pstanley55 (AT) hotmail (DOT) com wrote: Quote: On Sun, 15 Apr 2007 07:25:50 -0400, Ron Rosenfeld ronrosenfeld (AT) nospam (DOT) org> wrote: I've not seen an approach with advisory vertical guidance that violates a stepdown fix. The GP in these instances is, on Jepp charts, represented by a light dashed line, and a GP angle notation. So, if you are using Jepp charts, you can verify this. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) Ron, are you able to provide us with some examples? Stan Sorry Ron, I mis read your post. Everyone please disregard. 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