VGSI and ILS glidepath not coincident
09-20-2013, 08:43 AM
#1
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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.
09-20-2013, 08:55 AM
#2
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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
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
n. VGSI and IAP glidepath angles/vertical descent angles should be coincidental (angles within 0.2 degrees and TCH values within 3 ft). Whenever a published glidepath/ descent angle or TCH is not coincident with the VGSI angle for a runway, use the applicable note below.
09-20-2013, 09:07 AM
#5
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Originally Posted by Taildragger86
Thanks for the reply and the reference! I can get on board with that
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!)
09-20-2013, 11:08 AM
#6
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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.
09-20-2013, 11:14 AM
#7
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Originally Posted by Taildragger86
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.
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.
09-23-2013, 03:13 PM
#8
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Originally Posted by USMCFLYR
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.
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.
09-24-2013, 01:08 PM
#9
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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).
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).
09-27-2013, 07:25 AM
#10
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Originally Posted by block30
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.
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