Approaches at POU

[Jay Alson]

Hi all,

An IFR Approach plate design question for the group.

I'm looking at KPOU and specifically at the VOR-A and the VOR-24.

Both similar approaches, the VOR-A being a circling approach because the descent angle is too much for a traditional straight in approach, and the VOR-24, pretty similar, is a straight in approach with a lower FAF making it a reduced descent angle.

My question is why do we think the minimums are higher on the straight in approach (940 ft) vs lower on the VOR-A circling (760 ft).

Jay

[John O'Shaughnessy [FCM]]

My question is why do we think the minimums are higher on the straight in approach (940 ft) vs lower on the VOR-A circling (760 ft).

Hi Jay - Great to see you at Oshkosh!

I've been going back and forth between those two plates, looking for clues. I notice two things - one, the VOR RWY 24 is noted DME REQUIRED. I also note the missed approaches are different. I also see the VOR 24 doesn't show time for the approach (thus the DME requirement, I guess).

But -- I really don't know! I'm guessing someone closer to the area (Scott?) might have a good idea.

John

[Scott Dyer HPN/NY]

VOR24_Obstacle_Detail.png VOR24_Obstacle_Detail.png

Hi all,

An IFR Approach plate design question for the group.

I'm looking at KPOU and specifically at the VOR-A and the VOR-24.

Both similar approaches, the VOR-A being a circling approach because the descent angle is too much for a traditional straight in approach, and the VOR-24, pretty similar, is a straight in approach with a lower FAF making it a reduced descent angle.

My question is why do we think the minimums are higher on the straight in approach (940 ft) vs lower on the VOR-A circling (760 ft).

Jay

Jay -- Beats me. I saw this inquiry this morning and was hoping some bright idea would come to my head....no such luck. I've looked at the source documents for each approach (the Form 8260s), which don't help me. I've sent an email to Wally Roberts to ask for his input, I'll let you know what he says.

There is a 621' obstacle just west of the VOR on the VOR24 chart (detail below), and that obstacle isn't present on the VOR-A chart. I wonder if that factors in?

Scott

[Jay Alson]

John - great to see you at OSH too! Thanks so much for the hospitality for my friends and me! What a great time.

Same! I'm puzzled too on that one.

Jay

[Jay Alson]

Thanks Scott! I'll do some more digging and see what I come up with.

[Scott Dyer HPN/NY]

Thanks Scott! I'll do some more digging and see what I come up with.

Jay -- As I mentioned last night, Wally couldn't say what the controlling obstacle was for either approach, which would drive the MDAs. I'm suspicious of the "new" obstacle on the VOR24 being the culprit.

[Jay Alson]

Thanks, Scott. Same here. It's odd that they're in one and not the other. I tried to look on Foreflight near POU (not the approaches) for obstacles but it's not really clear where those are.

It also could be because of the missed approach procedures (the VOR 24 is a climbing right turn immediately from the MDA of 940 whereas the VOR-A is a straight climb to 1500 then a right turn). Also maybe it has to do with the holds too. It seems the VOR 24 holding procedure gets you out of the way for someone else to potentially shoot the approach whereas the VOR-A puts you right over IGN. Not sure.



Below are a few theories from a friend/CFI (John - this is from my friend Dan who you met at OSH)

'A few theories:
(1) It has to do with the missed approach procedures being different and obstacle clearance during the missed approach segment. Now why are the missed approaches different? I don’t know for sure.

(2) Maybe straight in approaches are required to have a decent angle of no more than some value. In order to meet that requirement, the VOR RWY 24 approach uses 1400 as the altitude at the final approach fix, but this brings obstacles along the final approach course into the required protected volume and requires that they give a higher MDA. Not the best theory because you could immediately descend to the MDA right after crossing the FAF on either approach. So if there are obstacles there, why aren’t they problematic in both approaches?

(3) Same as above but the lowest they can go over IGN is 1400 but then using the max decent angle, they get an MDA that’s higher. I don’t think it’s this one because the descent angle is 3.41 degrees, which seems like a weird number to be the max angle.

(4) The only other difference is that the missed approach point is timed on the VOR-A vs. identified based on a DME fix on the VOR RWY 24. But I don’t see why a less precise method of identifying the MAP would result in lower minimums.'