[bigginsking]

So I noticed a while back that "advisory glide slope" disappeared from GPS 17 at KSEE, my home field.

I thought something broke... but after flying recently with an instructor during an IPC I found out that the new LP approaches(that sometimes have lower minima) do not support advisory glideslope, at least the Garmin 430 LP implementation doesn't support advisory glideslope.

Background: For the guys that upgraded to WAAS, it was a pleasant surprise that all the non precision approaches suddenly had glideslope added, this allowed you to easily set up a stabilized approach much like an ILS on any GPS approach as long as you kept in mind that the baro altimeter and horizontal position was the actual guidance for where you belong vertically. You could still "chop and drop" but the 430 would connect the dots and give you "advisory vertical guidance" allowing for the hallowed stabilized approach.

LP came along and the FAA decided that this advisory glideslope business just has to go away. So in 2009 when Garmin implemented the LP approaches in the 430 they deleted the glideslope.

Then in 2011 the FAA recognized their mistake and published AC 90-107 and now allows advisory glideslope.

So I thought I'd see what Garmin's position was on this. The answer is below. I think basically they are saying 430 owners shouldn't hold their breath.

I suspect that more and more LP approaches will be coming online...

Bummer.

Bill
N84WJ, RV-8 915 hrs
rv-8.blogspot.com

Here is the response from Garmin.

Brief description of the problem:
Good Afternoon Sir,

While we understand the FAA's position on using advisory guidance the option to use it while flying a LP approach is limited by software. The advisory circular you quote was published on 2/11/11, while the GNS software that was first compatible with LP approaches dates back to 2009. It wasn't until the last 6 months or so that LP approaches had enough presence to disrupt LNAV+V approaches replacing the +V with lower minimums.

At this point the +V advisory guidance cannot be made available to you until/unless new software is made available for the GPS device that is being used. Garmin is aware of the impact that these changes have made on flying these approaches and will accommodate you as soon as possible. Please be aware that the process required to release new software is a long one and this feature may be some time down the road. I am not in a position to confirm if and or when this feature may be returned to your product. Please stay tuned for potential future S.W. updates for your GNC 430W.

Best Regards,​

 

[aerovin]

LP came along and the FAA decided that this advisory glideslope business just has to go away. So in 2009 when Garmin implemented the LP approaches in the 430 they deleted the glideslope.

I think the comment above does not accurately reflect the technical decisions made when considering making an advisory glidepath available for an instrument approach in an IFR database. My line of work slots right into this, and while this response is completely unofficial, I would suggest the following:

An LP type approach is usually an "LP" and not an "LPV" for a reason: it has an offset final that does not allow a glidepath, and/or there are penetrations by obstacles of the standard obstacle surfaces provided for precision-type approaches (i.e. ILS). The specific situation that raises concerns is when flying below the MDA on the approach, where the pilot is wholly responsible to "see and avoid" obstacles. The pilot is in the visual part of the approach. However, knowingly providing the user with an advisory glidepath that has significant obstacle hazards may not be in the best interest of flight safety, so the FAA has taken a closer look at this and, through the flight inspection process, has been removing vertical descent angles from LP and LNAV approaches where "see and avoid" obstacles clearly penetrate the glidepath. It remains the pilot's responsibility to provide obstacle clearance while operating below the MDA but, whether technically correct or not, perhaps there is some value in removing an advisory glidepath that will take you into a line of trees at night.

With respect to KSEE at San Diego, the approach is both offset to Runway 17 and there are obstacle issues. The RWY 17 VASIs are set at 4 degrees due to obstacles, yet the advisory descent angle is 3 degrees. You cannot land on RWY 17 at night if those VASIs are out of service because of those obstacles. The MDA is nearly 1000' AGL, so there is in excess of three miles on a 3 degree glidepath while operating in the "see and avoid" obstacle environment. I don't have specifics on the situation at KSEE so I can't comment directly, but I would suspect there are reasons if the advisory glideslope is not available.

There are many factors in creating safe instrument approaches and the process is continually evolving but the goal remains the same.

 

[bigginsking]

No Advisory Glide slope on LPs

Thanks for the info Scott.

The nuanced situation of sometimes Advisory GS is appropriate and sometimes not doesn't jive with the answer from Garmin: they do not provide advisory GS on LP, doing so will require a software upgrade.