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Hello.

I have a question about 'GS' in my RNAV(GPS) Approach Chart.

Usually, (Including PAPI, VASI whatever...) Normal Glide Descent Angle means 3.00 degree.

but some 'GS' says 3.07, 3.04, 3.09 even 7.75 in KSBS airport. (Picture above)

In this case, What does mean 'GS' exact ?

As far as I know, it's 'GS' means draw an imaginary line extend from Touch-Down Foot marker (1,000ft marker) to FAF for Non-Precision Approach. (Even do I Step-Down Approach ? I also wonder.)

but someone says, it's a line extend from 1,000ft marker to VDP,

and another one says, it's a Normal Descent Rate when PAPI indicates 2white-2red. (Exact Center-line of PAPI Glide Slope. I know approximately 0.4 of marginal has exist on PAPI for 2White-2Red (2.81-3.19)

If the last one's word is true, an airport have a 7.75 GS, like a KSBS Airport, then the PAPI of KSBS airport indicates 2white-2red when I follow the 7.75 GS ?

Waiting for your answers. Thank you.

BEST

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Are you asking about the specific term 'GS'? I don't see that on the chart in your question.

The angle symbol and the 7.75 are explained as a Visual Descent Angle in the Chart Users Guide.

A VDA and TCH may be published on non-precision approaches. For Copter approach procedures, a Heliport Crossing Height (HCH) will be depicted in place of the TCH. The VDA is strictly advisory and provides a means to establish a stabilized descent to the MDA.

VDA image

So it is an aid for maintaining a stabilized approach that should put you at the MDA at the correct point.

If the last one's word is true, an airport have a 7.75 GS, like a KSBS Airport, then the PAPI of KSBS airport indicates 2white-2red when I follow the 7.75 GS ?

No. In fact it's called out on the chart: "VGSI (Visual Glide Slope Indicator) and descent angles not coincident". So they do not match. You can look in the chart supplement for the airport and see what the actual angle is. For KSBS runway 32, the Glide Angle (GA) is 4 degrees.

RWY 14–32: H4452X100 (ASPH–GRVD) S–50, D–60 HIRL

RWY 14: Rgt tfc.

RWY 32: REIL. PAPI(P2L)—GA 4.0º TCH 40´. Thld dsplcd 600´.

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  • $\begingroup$ So GS basically stands for "Glide Slope" in this context? $\endgroup$ – user12007 Mar 14 '19 at 7:17
  • $\begingroup$ GOT IT !! and I might be little confused about 'GS' and 'VDA' in context....... and.... yes, yes, you're right. The words which I used 'GS' in context, was 'VDA' actually. Thanks :D. And I have a one more question. can you let me know 'VGSI and descent angles not coincident' ? As far as I know, All PAPI of USA indicates 2W2R on 3.0 degree path. but as you know, For KSBS R32 says 'GA' is 4 degree. Then In this case, If I descent with 4.0 Degree, the VGSI Indicates 2W2R in lieu of 4W? or just 4W?..... Then How can I find I'm on gilde path(4.0) or not ? $\endgroup$ – JAMES WON Mar 14 '19 at 8:42
  • $\begingroup$ 3 Degrees is nominal for PAPI, not required. For obstacle clearance, it may go up to 4 degrees. See faa.gov/documentLibrary/media/Order/… Page 5-7, note 1 $\endgroup$ – BowlOfRed Mar 14 '19 at 16:01

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