# How is a prevailing wind/average temperature study conducted to determine the runway direction and length for an airport?

A popular airport near me (KMYF) has two parallel runways, 28/10 R/L and a crosswind runway, 5/23. Almost always, 28R/L is in use. I'm sure they knew that there was generally a sea breeze in the area, and the wind typically will be right down the runway or within 10-20 degrees of centerline.

I'm sure they do prevailing wind study for the area, and my questions are about the study: What are the specifications for the study? Does the study vary in length depending on location? Is there a standard study battery of tests that they use, and do they test things like average temperature during the study to determine runway length (to maximize utility during high density altitude operations)?

• it will also depend on available flight-paths around existing infrastructure Jan 28, 2014 at 15:20
• Oops! KMYF has runways 28/10, not 27/10. Jan 29, 2014 at 16:34
• @ratchetfreak good point. What gets priority? I mean if they do a prevailing wind study and figure out that it's best to have 28/10, but that traffic pattern puts it into terrain or other hazards, would they switch the runway, or would they look for a new location? I guess my question is, what is all involved in the study? I'd imagine the first thing is looking at existing infrastructure, then figuring out the directions and lengths? I'm interested in a high-level overview of the whole process. Jan 29, 2014 at 19:21

Basically you start by figuring out what kind of aircraft you want to operate at the airport, and establishing some basic wind limits (specifically, the maximum crosswind and tailwind components you want to deal with).

Then you call up NOAA's "National Climate Data Center", tell them where you're looking to build your airport, and see if they can have wind data for the location you're looking to build on.

If NOAA doesn't have data you have a couple of other options -- another nearby airport's wind analysis can be used (if the topography doesn't vary that much and the wind analysis is "recent"), or you may have to perform a wind survey which basically means placing a anemometers on the site to record the wind speed and direction for a year.

Armed with collected wind data you tally up the number of observations in given wind speed ranges and mark them down on a "wind rose".
You then place your runway(s) on the wind rose so that they're aligned with the prevailing winds and determine your "wind coverage" - the amount of time the winds at your site are within your crosswind and tailwind limits.

The advisory circular I linked to shows you how to do this by hand, but there's also software to do this which is how most folks do it. The FAA even has a handy web form which will generate the wind rose and runway/crosswind limit bars for you.

Note that this is just the wind part. As you've alluded to there are a number of other considerations, like terrain: If the prevailing winds favor runway 36, but runway 36 points right at a mountain a mile from the field you might have to align the runway 33 or 03 and sacrifice a perfect headwind for not having pilots fly into the mountain.
Also as ratchet mentioned the airspace around your proposed site may influence your runway layout and types of operations. There's a separate FAA office that deals with "Obstruction Evaluation and Airspace analysis" and a process to go through to ensure that your airport is not deemed "Objectionable".

Also as you alluded to in your question there are other considerations like density altitude (local temperature and humidity trends) which will influence design factors like runway length - there's another advisory circular (AC 150/5325-4B) that talks about runway design criteria, including length considerations.

For even more than you ever wanted to know about airport design you can check out the full 150-series of Advisory Circulars, which all deal with airports in some way (there are ACs on design, construction, markings, lighting, ARFF, and even how to qualify for and obtain federal aid).

• Not to forget a noise assessment... Jan 28, 2014 at 17:59
• @yankeekilo or the all-encompassing environmental impact study. Jan 28, 2014 at 19:03
• There are literally an infinite number of studies that may be required prior to constructing an airport (the local municipality may require a study on the effects of runway alignment on the migratory patterns of local slugs). This question is only concerned with wind and temperature though... Jan 28, 2014 at 19:08