IFR BC Approach

[Paul Sharp]

Here’s something interesting that others may have already gone through, but it was a new experience for me, and I’m posting it in case it’s helpful for other pilots.

I have a Garmin 430. I am IFR rated and keep current, etc. I had read about practicing with the IFR GPS boxes before using them and have done a lot of practicing with the thing in the years since I had it installed, but usually the more common types of approaches. And it happens that most of the time in the past few years I find myself in VFR conditions.

A couple of months ago I ended up going IFR to Boise. And interestingly, they assigned me the LOC BC 28L approach. Never had one of those ever before except once during initial IFR training years ago, but I plugged it into the Garmin and flew the approach. I found it interesting that the readouts for distance weren’t very intuitive. They are labeled by Jeppesen with waypoint ID’s that don’t necessarily correlate easily with the chart. Fortunately, with radar required and ATC looking over things it went fine. But I had questions in my mind about the approach.

I called Garmin about 4 times since then going over this approach and asking questions about how it works in connection with the GPS. It took that many calls to get clear answers out of their technical support. One guy seemed quite knowledgeable and the other one seemed to have to ask the other one about it. Still it took a while to narrow down the details. If you have your nav tuned to IBOI (the localizer – 111.1) then you might think you’d see DME readouts of IBOI, corresponding to the chart’s stepdown fixes. But not so. Jeppesen has created a waypoint for each stepdown fix and you see the readouts to each as you approach it. And if you don’t know the naming and how the waypoint names correspond to the chart you can be doing more heads-down than is good. True, you can review the approach fixes as soon as you load it, and that’s something I think I’ll be doing more of in the future. But you’d still have to get it fixed in your mind what those identifiers are on this type of approach.

If you select the “vectors” transition, you won’t see some of the fixes loaded, but only from the FAF inward. So that can also be confusing if you don’t connect the dots on what is or isn’t loaded ahead of time. And you can’t practice this one with the downloaded simulator on a PC because the latest database is still too out-of-date to include the fixed on this approach. I think you could practice it on the GPS itself in the aircraft in simulator mode, but that often may not be very practical.

I suspect that other similar approaches are treated in the same manner. It proves to me what has been said about the need to practice with these boxes is very valid. You don’t’ want any guesswork while coasting down the final approach course in the soup. I’ve been flying too many straight-forward ILS approaches lately, I think. Many of the flight instructors I’ve flown with don’t know as much about the box as I do, so you can’t necessarily count on them helping in your reviews or training.

[travis]

Hi,

Just a quick comment... I am an instructor for Bombardier Aerospace in the Lear 45 so I deal with this quite often. The Waypoints are not named by Jepp, they are named by the FAA. With GPS and now WASS the FAA is trying to name all the intersections in the database with 5 letter words (trying to get away from names like "OSI24" OSI is the Woodside VOR and the intersection is @ 24 DME)! As far as the DME is concerned... The map on the GPS (I have a 530 in my Skymaster) is GPS derived in fact there are no true DME receivers in any of the Garmin GPS products. All "DME" in this case is actually GPS calculated distance. In other words there is never a slant range error. All that said, when you are looking at the map the GPS is showing a course and range from point to point (the only thing that GPS knows) instead of a place / bearing / distance. So as you progress through a sequence of waypoints the Garmin will always show distance (different than DME) to the next waypoint. As opposed to the actual DME from the navaid.

Hope that helps a little

_travis

[Paul Sharp]

Yes I knew they were waypoints, etc. But when you look at them, unless you study the identifiers you don't know which is which and hence you can't relate your stepdowns to what's on the chart. I wasn't aware, however, that the FAA had named them. Actually for me it would be nicer if the waypoint names were related to the DME measurements as that makes them easier to identify and correlate to the paper chart. Maybe the chart will eventually come out with the waypoint names on it?

[travis]

So far as I know they are working on naming everything as they go. I think that they are working on replacing the DME oriented fix names first. Also they are buisy (re)building many RNAV (GPS) approaches with and without WASS.

Just so yall know there is a wiff of change on the wind. The old MLS arcing final type approach is (will be) the new flavor. Checkout the RNAV (GPS) Y 28R at KSFO. This is an experimental approach (SFO has many offset parallel approaches 28R&L like the LDA PRM 28R) the biggest part of which is the missed approach segment that is impossible to fly IMC without GPS (no other conventional navaid will provide positive course guidance on an arcing segment.) The new(ish) TAA GPS approaches are the start allowing a "cruise" clearance from an enroute controller taking the approach control out of the system. The next evolution will allow 180 arcs to final on a GPS glide slope (LPV) to CAT I minimums!!! Hot stuff. I hope Garmin can get my box a WASS conversion soon!

Any hoo thats just a fun tidbit form todays Lear 45 class for free for those with two in the middle.

_travis

[gwengler]

I have a KLN94 plus MX20 so this might be slightly different. To get the correct DME reading I go to the INT (intersection) part of the GPS. Only there do I find the DMEs (IBOI in this case). By just calling up IBOI on the intersection page, I get the usual information about distance, bearing, frequency etc. I leave that on the display to get the actual DME distance which corresponds with the chart. That way there is no confusion about which distance is displayed as you had described.
Hope that helps,
Gerd, ATP

[travis]

Agin this is a referance to the GPS database position for the waypoint not an actual DME reading from the ground! But yes on the Garmin there is a nerest page that will give the distance to all the listed waypoints. Aslo on the 530 there is an optional screen on the left under the freq's that will display the ident, radial and distance to a VOR or ident, location and distance form a LOC.

_travis

[Paul Sharp]

Looking at the intersections page is a nice suggestion, I think. Technically, since IFR GPS boxes are legal to substitute for DME, aren't they accurate enough to go by? I can't imagine the FAA saying "You can do this now, but by the way, it isnt accurate enough to use."

[hharney]

Are you sure an IFR Cert GPS is a legal DME? I didn't think so.

[Paul Sharp]

Yes, it is a legal "substitute." (Not just any GPS but a legally-installed, IFR-certified model.)