Airport Layout Question...

killbilly

Vocals, Lyrics, Triangle, Washboard, Kittens
I've always assumed that the runway layouts were put down to align with the prevailing winds of the vicinity - for example, most airports in TX have a general north-south alignment because our winds are usually like that.

But I've noticed a couple of fields where they had a crosswind runway with an ILS, and only on that runway. Why is that? Why not install the ILS on the runways most often used?
 

USMCmech

Well-Known Member
Sometimes there isn't enough physical space for the ILS components.

Also, perhaps the winds are out of the other direction when there are low ceilings.
 

Seggy

Well-Known Member
Could literally be a million reasons from noise abatement procedures, terrain for that ILS, setting up approach lights, federal funding for ILS approaches, etc.
 

killbilly

Vocals, Lyrics, Triangle, Washboard, Kittens
Also, perhaps the winds are out of the other direction when there are low ceilings.
This is what I was thinking, but I dunno. Thus the question. Anyone around here familiar with airport planning and construction? Inquiring minds and all that...
 

OldTownPilot

Well-Known Member
Yep, probably do to the "bad weather winds"

In Maine, 99% of the ILS are on southeast facing runways, while 80% of the time you land to the northwest. Its the 20% of the time that when the winds are blowing like that you 'need' the ILS.

Now this 'crosswind' runway that you speak of, is it of similar length to the 'main' runway?
 

mhcasey

Well-Known Member
Bill if you're thinking of San Marcos I think it's because a 17ILS would be bringing guys awfully close to the departure end of AUS.
 

muffinman

Well-Known Member
Bill if you're thinking of San Marcos I think it's because a 17ILS would be bringing guys awfully close to the departure end of AUS.
This is true, Austin approach wont even let you fly the published missed on the chart because it takes you too close to their flow of traffic. Most of the time the turn out is all you follow then they start providing vectors.
 

Scandinavian13

New Member
Sometimes there isn't enough physical space for the ILS components.

Also, perhaps the winds are out of the other direction when there are low ceilings.
More the former than the latter, but it's a consideration.

Obstacle clearance?
Sometimes the case, yes.

Could literally be a million reasons from noise abatement procedures, terrain for that ILS, setting up approach lights, federal funding for ILS approaches, etc.
Exactly. Most of the time, it has to do with meeting the FAA's requirements and there are many. Often, it's an issue of runway length and approach clearance (glide-path gradients). Sometimes, as above, it's related to obstacle clearance - there are several zones for the precision system that must have certain clearances. Outward from the OFZ, there's a conical surface defined by TERPS. It surrounds the runway, ascending on all sides, but the most important sides are the ends, obviously.

This is what it looks like when you plan it all out. Mind you, this is only for a LOC, but it's similar (just a bit more lax).
http://www.leesburgva.gov/Services/airport/LayoutPlan/2007_Layout6.pdf

The airport depicted is JYO, which I didn't work on, but I worked on a few others when I interned with Cambell & Paris. You can actually see the orange lines on the diagram saying "Future 50:1 Approach Surf," which hints at a future ILS. We dropped Leesburg's contract at the end of the term, so I'm not sure whether or not they still plan on it.

If you have any airport planning-related questions, shoot one at me. If I don't know it, I can always forward it on to the guys I worked with.
 

killbilly

Vocals, Lyrics, Triangle, Washboard, Kittens
Bill if you're thinking of San Marcos I think it's because a 17ILS would be bringing guys awfully close to the departure end of AUS.
Actually, it was one of the airports near Waco. I had my car GPS in aviation mode on the drive back from Dallas this week. One of the graphics it shows is the ILS-approach thingy (where the point of the long triangle touches the runway threshold) and I noticed it was only shown on an east-west runway, but not the north-south. Can't remember which one it was, though. Looked a bit on Airnav but didn't find it....
 
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