I live near Harry Reid Airport (FKA McCarren airport) in Las Vegas, directly west of the airport. My apartment faces west. The vast majority of the time, I can look out my window or walk my dog and see planes lined up to come in for a landing (sometimes 7 or more at once!) and watch them fly eastward overhead on their descent. But sometimes, every now and then, the planes go the opposite direction and I see them going WEST and gaining altitude (so clearly they have taken off). WHY do they seemingly randomly switch the runway direction? Weather and wind does not seem to play any factor as I’ve tried to pay attention to if I only see them going the other way when it’s cloudy or windy and no… It truly seems random. Why do they do this? It baffles me.
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Typically airports will try to have aircraft take off into the wind, so if the direction of wind shifts the airport can switch up the direction aircraft take off and land.
Aircraft need to move a certain speed through the air in order to take off so if they move into the wind they are getting a boost, while if they take off with the wind at their back they need to accelerate even more. Similarly if aircraft are landing with the wind at their back they will need to contact the ground moving faster than if they were flying into the wind.
When possible, planes try to take off and land into the wind. This is because it allows the plane to maintain more lift at a slower speed, and the headwind helps the plane slow down once it’s on the runway. So when the winds shift directions, deepening on the layout of the runways, airports will often change which runway direction planes use for landing and takeoff so they can still land and takeoff with a headwind. The wind might not be apparent to you but it could still be enough to benefit the planes.
I’m a Vegas plane watcher too and sometimes when the wind is light, traffic will take off to the east. Since this cuts down on taxi time from Terminal 1 to the end of the runway (it can be almost 2 mile long taxi going to the “usual” end.)
Also, flights going East save fuel and time because they don’t have to turn 180° to head East.
It has to do with the direction of the wind.
As a pilot, you want to want to take off and land with a “headwind”, that is, the wind in your face rather than at your back. This forces more air across the wings and control surfaces of the plane, giving it more lift, which means they don’t need as much actual speed to take off and land.
For this reason, most airports will have at least one runway that runs roughly north-south, and at least one that runs roughly east-west. That way, no matter what direction the wind is blowing, there’s a runway that runs in roughly the right direction to give pilots a headwind.
This happens famously at LAX Airport in Los Angeles. 95% of the time the wind is from the west or southwest off the ocean (in fact the airport was put there on the coast because of the reliable west wind), and the planes both take off and land pointing west. I live 3 miles south of it, with a north facing window, so I can clearly see the planes.
On days when it’s raining, storming, or there’s an offshore wind (common in the fall and winter), they reverse the airport, and planes land from the ocean and take off toward the city. They also do a half reverse each night to reduce noise pollution, both landing and taking off over the ocean.
The only thing we can sure of is that it’s not random. There are multiple factors that air traffic control (ATC) uses to determine the appropriate runway(s) to use for departures and landings, the biggest being wind direction and speed. At the airport in my city, landing to the southeast is preferred because of mountains and because it’s the runway with the ILS (instrument landing system) approach. Also, we have a lot of flights that are eastbound. So they’ll prefer use this runway, even if there’s a slight tailwind, instead of going the opposite way on the same strip of concrete, to the northwest.
I can’t figure out why ATC would have the majority of landings (and therefore takeoffs) to the east at Harry Reid. Commercial airliners at busy airports, even in good weather, fly instrument-guided approaches (known as “instrument approaches” or “instrument approach procedures”), and only one out of the 13 such procedures at Harry Reid are for an east-pointing runway. This tells me that surface winds out of the east at Harry Reid are uncommon. The only way I can explain this is that you’re not straight west of the airport. Are you in the Spring Valley/Sovana area, or perhaps over by Whitney? If you’re in the North Las Vegas area, then there’s an almost straight-in approach to runway 19L.
Airplanes always land and take off against wind direction. So on a east-west runway, if the wind is blowing from easterly direction they take off towards east and they switch the entire airport traffic around if the winds are from westerly direction.
I was actually waiting to take off at an airport a few days ago and there was a short delay because the wind direction changed, and air traffic control was having planes take off in the opposite direction instead. So it definitely does factor in
Weather and wind are the largest factors. Here’s the aviation weather for KLAS: https://aviationweather.gov/metar/data?ids=klas&format=decoded&hours=0&taf=off&layout=on Flightaware, flightradar24, or any of the traffic tracking websites/apps can show you the flow. LiveATC publishes audio feeds of the radio frequencies, but it takes some studying to learn to make sense of the calls. Tower might announce the winds direction and speed with the takeoff and landing clearances because it’s so important for flying the plane.
Here’s CGP Grey on runway numbers. He touches on the wind rose https://youtu.be/qD6bPNZRRbQ and generally taking off into the wind.
If there are thunderstorms on one side of the airport, they might allow a tailwind in order to take off away from it.
The 180 isn’t that big of a deal: https://en.wikipedia.org/wiki/Airfield_traffic_pattern still applies.
The FAA makes the pilot training handbooks available as free PDFs: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation the Pilot’s Handbook of Aeronautical Knowledge and the Airplane Flying Handbook are the two main books for the basics.
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