VGSI and ILS glidepath not coincident
 

Does anyone know what this means in the notes section of ils approaches? I've asked many people I fly with, but I've never received the same answer twice. Some clarification would be nice.

The electronic glideslope and the VGSI glideslope are not exactly coincident.
The difference can be fairly small 0.2 angle and/or 3 feet difference in TCH).
Basically it is a caution that you might pop out of the weather right at mins on a Cat I ILS at 200' HAT where your instruments were showing you exactly on glidepath and you see for example slight high on a PAPI 4 bar system.

This might help in the explanation:
http://aeronav.faa.gov/content/aeron...GSI_Angles.pdf

Edit:
From FAA Order 8260.19E Ch 3

It simply means that the ILS and the visual glidepaths are not the same.

vgsi and ils glide path not coincident
 

Thanks for the reply and the reference! I can get on board with that

Now - - - GO FORTH AND EDUCATE! :D

A friend some time ago sent me a link to a thread on another forum.
He had experienced the situation I described above with being on/on flying the ILS but saw someting other on the VGSI.

The guy complained to tower and such but said they weren't interested.
IN fact - it very well may have been designed that way and th note on the chart *should have* allerted them to the fact.

If you experience the same and you see that the PA/VDA angle is more than 0.2 or the TCH's are more than 3' difference and there ISN'T a note - then you should use the POC information in the plates and let your concerns be known (there ARE errors in the plates and another set of eyes (the users) are welcome in finding the errors!):)

Good discussion. A related issue to this is the requirement in the PTS (ATP PTS change 4) with respect to landing within the touchdown zone (+500 / -250) feet from the Aiming Point Markings. This is much tighter criteria than the actual touchdown zone. When the ILS GP and VGSI are not coincident, there exists the potential for the pilot to want to "duck under" the GS and get on that VASI/PAPI as soon as possible.

Taildragger -

I'm curious what answers you were being given.
In the UPS accident thread there were good discussions about VGSI systems, TERPS criteria for different approaches, and advisory vertical descent angles - and there seemed to be a lot of eye opening in that discussion. I'd like to know what the flying public's misperception of the note in this discussion entails.

Why aren't the PAPIs/VASIs synched up to the glideslope then? Is it discussed in the UPS crash thread? I haven't been following that one. Thanks for your wisdom.

I was taught many, many moons ago that the VGSI lights were installed to be compatible with a normal touchdown from the non-precision approach for that particular rwy....while the ILS descent angle is somewhat of a result as to where the hardware can be placed. Way back memory machine thinks the acceptable tch was in the 45-70' range (haven't been able to find the book answer, just the displacement from the rwy which is of no particular use to me)

But the norm is for a 50' tch so majority of vgsi and ils will be consistent--and for those that aren't, flying either should, keep me safe provided I'm close to the field (norms are 4sh for vgsi, and 10 for the glideslope)

Better question is what to do when the VDA angle on a non-precision approach is not consistent with the VGSI (eg see LOC 27 at KSAN).

Most often the reason is due to siting restrictions for one of the systems (GS antenna or VGSIs). Each system has its' own RPI (for the GS) or RRP (for the VGSIs). Again - the difference in calling them coincident is small (0.2 deg or 5' of the respective calcuated TCHs). Very hard to see with the eyeball for most, which is why we get a lot of comments that there is a note on the approach plate but the glidepaths were actually matched up when *Joe* pilot flew it yesterday.