# 1. Why does the glide slope guide you down to 0.7NM away from the runway? 2. Best way to circle from 28 to active runway 36?

1. Why does the glide slope guide you down to 0.7NM away from the runway? 2. Best way to circle from 28 to active runway 36? Note parachute jump site takes place on SE corner
• It would be a better idea to separate this into two questions
– Jamiec
Jun 6, 2023 at 20:41
• I agree, and the question about merging a circling approach with VFR traffic is well covered here: aviation.stackexchange.com/questions/99358/… Jun 6, 2023 at 22:33
• Also, consider clarifying why you are asking about 0.7nm, is it because you think that is far enough out that at 313' AGL you ought to be able to press in further, break out, and still make a safe landing? (Because we don't know your background or knowledge level, and the short answer is "because that is the MAP...") Jun 6, 2023 at 22:38
• Note the gray triangle on the profile view is not vertical guidance; it indicates there are no obstacles in the visual segment after you reach the MDA (or DA, as appropriate). Jul 7, 2023 at 15:55

## 1 Answer

First off: it doesn't. The approach has no vertical guidance. Once you've passed JIBDO you can drop all the way to the MDA as quickly as your plane is capable of. Below the MDA there is no guidance at all- you must have sighted the runway environment in order to descend below the MDA.

Also, despite how it is drawn, a constant descent angle of 3.06 degrees from the FAF will get you to the runway at TCH, and won't crash you into the ground 0.7nm short of the runway:

$$\text{VDA} = \tan^{-1}\left(\frac{\text{FAF altitude-TCH-TDZE}}{\text{distance ZURBU to threshold}}\right)= \tan^{-1}\left(\frac{1953~\rm feet}{36464{~\rm feet}}\right)\approx3.06^\circ$$

It's calculated as though you turn directly towards the runway threshold as soon as you cross the FAF. You wouldn't normally fly it that way (certainly not if you're flying it to minimums!), but using the same angle flying all the way to the MAP and then to the threshold still puts you at a TCH of 31 feet. Not underground as the profile view would have you believe!

The final approach course here is 20 degrees offset from the runway. If the final approach course took you directly to the runway threshold, it wouldn't leave you any room to maneuver to align yourself with the runway. So the final approach course has to intercept the extended centerline of the runway with some additional room for maneuvering. In this case, it is set up 4499 feet from the threshold, a little over 0.7nm.

If you pass through the extended centerline of the runway without sighting it, it's unlikely that you are going to, and it would greatly increase the maneuvering required to land safely even if you did. So the missed approach point is set on the extended runway centerline.

• Interesting that the plate states that: "VGSI and descent angles are not coincident" when rwy 28 does not appear to have a VGSI. (According to the rwy info on airnav.com.) @michaelhall
– user22445
Jun 7, 2023 at 0:03
• @757toga I guess they can't be coincident if one doesn't exist! Jun 7, 2023 at 0:04
• The procedure was made in 2014. It’s likely that there was a PAPI then to RWY 28, which is why the procedure form has that note. Or it’s an error. See the procedure’s 8260-3 form here: faa.gov/aero_docs/acifp/NDBR/2016062128729904002-X51-NDBR/… Jun 7, 2023 at 3:21