Whether e.g. ORD is launching and recovering to the east or to the west is decided by the wind. And in light enough winds by prevailing traffic convenience or noise abatement.
But of ORD’s six east-west runways, which ones are used for takeoffs and which for landings is a matter of taxi flow convenience.
If you have a pair of adjacent runways it is much more efficient to use one exclusively for takeoffs and one exclusively for landings than to use each for a mixture of takeoffs and landings. So the debate becomes which of the two does which role. The answer generally depends on the arrangement of terminals and taxiways relative to that runway pair.
As well, ORD is an entertaining example. It has been undergoing a gigantic rebuilding to eliminate all but the directly east-west runways and to build more runways parallel to them. So it’s actually an anti-example of operating into the wind. 1980s ORD could do that in any of 6 directions. 2020s ORD is purely east or west. Plus a few takeoffs-only going southwest; the one oddball runway is only used for 1 of the 4 possibilities (take off or landing from either end). 2030s ORD definitely won’t be able to; it’ll be east/west only.
I think if the planners had a totally free hand, they’d have runways in multiple directions. Denver has scads of land; four north-south runways, and two east-west. If O’Hare is going to be all east-west, that may be because they’re stuck building on available land.
Sorta. Prevailing winds matter once they get high enough. Denver is prone to high winds in all 4 directions. ORD much less so.
At the time ATL was built they had free land in every direction. It’s purely E/W. When LAX was first built during roughly the WWII timeframe it was the same story: obtainable land in every direction and they chose a purely E/W orientation.
As a separate matter, the sensitivity of airline-type airplanes to high crosswinds is much less now than it was in the pre-jet era. I expect that if the USA ever builds another greenfield major airport it’ll be bi-directional, not multi-directional.
Good point, looking in the Abandoned & Little-Known Airfields page you find it was not rare in the early days of even having paved runways at all to have a triangular layout.
For funsies have a look at historic overhead pics of London Heathrow which started with a hexagonal layout that must have got 1950-ish conspiracy theorists nicely worked up.
ORD = O’Hare in Chicago mentioned upthread was a sorta hexagon when I started in the biz in the late 1980s. 2 east / west, 2 northeast / southwest and 2 northwest / southeast. Many arranged to cross each other either near the middle or near one end. The irregular hexagon in the center housed all the passenger facilities.
A total dog’s breakfast of random. Barely controlled or controllable chaos. Such fun.
The required turn radius at high speeds is silly. Which suggests a truly huge circle occupying many square miles of land.
Being aligned with the wind is not that important. Besides, at what point during the takeoff or landing run are we supposed to be aligned? It won’t be all of it; that’s for sure.
Prior to the advent of GPS approaches a curved runway would be far more useful for takeoffs than landings.
Even now it’d take a bunch of design work to produce a flock of approaches at different azimuths ending on a curved runway. And some design changes to software on a lot of boxes on a lot of planes.
A steady crosswind is mostly a non-event. The pilot has to keep the mains centered to the runway. It’s the gusting that makes it a problem. More to the point, it’s the ginormous high-bypass engines that hang low off the wing. It limits how many degrees of wing movement before dragging an engine. As an example, I know of a 747-8 freighter crew that did multiple company mandated go-arounds because of a limit of 10 degrees. They were doing better than a 747-400 crew who landed on the first attempt.
The B747 has the outboard engines making things awkward. Twins, on the other hand, aren’t as bad as they look.
Here’s a ground contact diagram for an A321 neo (with the big engine nacelles).
The line “C” is where the wing tip will touch the ground. Note that for the nacelle to touch (“D”), the pitch angle has to be very low. Because the engines are well forward of the wing, the nose up pitch on landing helps keep them clear. The B737 might be more limiting with its shorter undercarriage.
A normal crosswind technique involving a decrab in the flare and lowering the upwind wing to maintain the runway centreline works well in all but the strongest of crosswinds. You can also land with some crab (5º) if necessary to prevent excessive bank.
The 737 is similar, but as you surmise the bank angles are a few degrees less because of the shorter gear.
For background, a properly flown landing on-speed with normal flaps should result in touchdown at about 5 degrees of pitch.
For the 737NG, the area corresponding to line C on the A321 diagram is all about dragging a flap track nacelle on the ground, rather than a wingtip. Those things hang way down at full flaps. At silly high pitch = 12 degrees you’ll drag at 10 degrees bank while at near zero pitch it’s 17 degrees of bank to drag.
The MAX is far more bank angle critical than the NG. The engines are bigger but more up & out of the way. The limiting factor is the very long lower winglet hanging down from a wing that’s already close to the ground. And like any swept wing, gets closer with increasing pitch.
At silly-high 12 degrees pitch the winglet drags at a mere 8 degrees of bank. Even all the way down at zero pitch the winglet drags at a rather small 12 degrees of bank.
All the above assumes a smooth touchdown. If you bang it on, the wings can flex a bunch so a drag can happen at less extreme angles.
Like the 321, dragging a 737 engine requires very low pitch and lots of bank. In fact on the MAX you can’t drag a nacelle unless you’re at negative pitch and high bank, wheelbarrowing along on the nosewheel. Which generally doesn’t end well:
Overall, the approved technique for high crosswinds in an NG is “Use a smidgen of ‘decrab and slip’, accepting whatever crab that leaves at touchdown.” The MAX technique is more like “Just think about decrabbing, but don’t actually do any. Just bang it on sideways; it’ll be fine.”
One of the pilots on all airlines (except Southwest) does walk around the plane and look in there. Anywhere from 1 hour to 20 minutes before departure. So considerable opportunity for somebody to sneak in there between that time and takeoff.
I would bet that most of these stowaways don’t get into the gear well at the gate. Instead they’re waiting along the fence next to the airport edge and make a dash for it when they spot an airplane stopped or taxiing slowly nearby and no other airplane close enough behind to observe and report the runners.
Run out there and get squashed by the gear while the plane is (or starts) taxiing.
Run out there and get inhaled by an engine.
Run out there, climb up into the well and discover there’s not really anything to hang onto so you fall out within a few feet of taxiing. Hint: best case outcome for all.
Get ensconced in the well and be dislodged during takeoff roll with all the bouncing and insane noise levels near engines at high thrust. Slide / tumble down the runway at up to ~150 mph.
Get ensconced in the well, unwittingly sitting on or holding onto the gear door. Which seems like a real safe place during the takeoff roll. After liftoff the door opens and drops you bombs-away style when the gear is selected to retract.
Get ensconced in the well, find something suitable to hold onto, survive takeoff and the gear doors opening, then be squashed like a bug when the gear comes up into the space you occupy. Or maybe it just crushes one of your legs, leaving your head and torso intact.
Survive takeoff & gear retraction, then notice how dark and insanely noisy and scary it is in there. And cold and rapidly getting colder. Much colder.
Pass out during cruise from lack of oxygen and slowly have parts of your brain die of hypoxia. While freezing too. Which loosens your grip on, well, everything. So you fall out when the doors open.
Somehow not freeze or hypoxia to death (probably a very short relatively low altitude flight), but with nearly frozen limbs & hands lose your grip and fall out when the gear doors open and the gear comes down.
Miraculously remain on board through gear extension, but be blown out of the well by the insane wind/turbulence in there during the last 3 minutes of flight.
Miraculously remain on board through touchdown, but be bucked out of there by the less than stellar landing. Now roll/tumble down the runway at ~140mph to a stop.
Make it all the way to the gate and be caught by ground crew then arrested by police.
Bottom line: A less that first class experience. Can. Not. Recommend.
The real wonder is that anyone anywhere in the history of aviation has survived a ride in a gear well. By comparison a cargo hold is warm-ish, pressurized, and impossible to fall out of.
