Simviation Forums

Hi all.
Are runways directions purposely built so "by design"?
Case in hand is Heathrow, runways 27 L+R and runways 9 L+R. Rwy 27 heads due West, Rwy 9 heads due East.
Logic dictates that when departing for USA, west, you will have been assigned rwy 27. Likewise, departing to Europe, EAST, you would be assigned rwy 9.
Is this indeed so in the real world?

I would say false

departure and approach runway selection is based on local traffic paterns, weather, airport procedures, etc.

maybee a real pilot can confirm ?
now i'm curious

The runway numbering is correct and corresponds to real world.

If you look, for example at Paris Orly with google earth, runway 26 is oriented 258° towards west. The rule is the closer number to the axis / 10. EG: Axis = 312°, runway number = 31.

The answer to your question is yes, but not for the reasons you suggest.

Runways are normally purpose built based on prevailing wind directions. This isn't always true though. Some airports may just be a runway placed in a convenient location based on terrain or local obstructions, but for the most part, it is prevailing winds that dictates the runway design. You want your runway to point in the direction that the wind blows most of the time, otherwise the runway could be effectively unsafe and useless if strong crosswinds are frequent.

For example prevailing winds in my region are almost always from a northerly direction (north or northwest usually), or when it's warm they are coming from the south. So the airport configuration is runway 13-31 and 18-36. We used to have a 07-25, but it was so rarely used that it got closed and developed into a new terminal and ramp area. Winds from the west are usually not to bad and runway 31 is ok. Winds from the east mean really nasty weather, and in that case most planes aren't gonna fly in those conditions anyhow (gale winds and t-storms). However with a north south runway configuration, 90% of the flights out of the airport are east or westbound. So you can see an east-west runway may seem like a good idea, until you consider that the wind doesn't often favour that layout in or region.

As for which runway is used for departing, it may occasionally be based on departing direction of the aircraft if conditions permit, but normally it is wind, aircraft type and instrument capabilities, and standard operating procedures of the control zone that dictates what runway is used for landing and departing (not always the same runway). For example runway 27 could be the active departing runway, but a pilot could request a different runway for convenience to get more of a straight out departure....not that the request will necessarily be granted, but it is certainly permissible to ask. Or a departure procedure for a specific type of SID is only available off certain runways so certain planes with suitable equipment on IFR departures would be using that runway.

Hope that helps.

" it is prevailing winds that dictates the runway design."

Excellent explanation thanks . This makes total sense and would by far be more logical to do than what my question implied. Thanks.
(Fascinating is the world of aviation)

Also, bear in mind that runway numbering can change over time: since the magnetic north is a floating, mobile thing, an airport's runway numbers can change. I remember when all those Runway 15/33s in the Puget Sound area changed to 16/34s. I've had to go into AFCAD and re-number various runways and starting positions, too, just to keep current.

A bit more detail from the real world:

There is a general rule about aviation wind reporting: If you read it, it's [referencing] true noth . If you hear it, it's [referencing] magnetic north.

All charts and textual sources (METAR, TAF, winds aloft, surface analysis charts, etc) use true north as the reference.

ATIS/AWOS/ASOS broadcasts, or any information a controller gives you over the radio, is magnetic.

Wind direction broadcast over FAA radios is in reference to magnetic north.

One exception to the "if you hear it" rule is that a Flight Service Station briefer will read you the winds referenced to true north, since they're just reading you the charts/textual information.

So, runway numbers reference magnetic north, which allows the pilot to use and confirm his compass reading, while written wind information refers to true north. For obvious reasons, controllers reference magnetic north so their information is consistent with the runway numbers and the pilot's compass.

(This is at least true in the United States... other countries may vary in some instances)

Perhaps more information than you want for simming but might help if you are hooked up to a real-time weather app.

This tip may not always apply, but make sure that the runway that you intend to land on matches with your compass EXACTLY. "Close" is not always good enough.



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