# What is happening when the airplane lands? **URL:** \ **Category:** Factual Questions\ **Created:** [October 12, 2010, 7:44pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909 "2010-10-12T19:44:58Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![pyromyte](https://avatars.discourse-cdn.com/v4/letter/p/d26b3c/32.png) [@pyromyte](https://boards.straightdope.com/u/pyromyte)\ **Post date:** [October 13, 2010, 1:40pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/41 "2010-10-13T13:40:10Z")
> [@EmAnJ](#): > > > [@mnemosyne](#): > > > > Hard landings are reportable events in Canada, and there is no report of one so far in the [CADORS](http://wwwapps.tc.gc.ca/Saf-Sec-Sur/2/cadors-screaq/m.aspx?lang=eng)for landings at Calgary this weekend. > > The hard landing was on the flight to Las Vegas. Is there something similar for the US? An official ‘hard landing’ is defined as landing with a vertical speed greater than 400 ft/min – [wikipedia](http://en.wikipedia.org/wiki/Hard_landing). I would imagine that is much harder than most passengers would describe as a ‘hard’ landing. In the US check the [NTSB database.](http://www.ntsb.gov/ntsb/query.asp) It has info on all _accidents_ and selected _incidents_ since 1962. I am guessing a hard landing would be classified as an _incident_, but I don’t know. ETA: after re-reading the wiki article that 400ft/min figure sounds more like an average decent and maybe is not used to determine hard landing v. regular landing. I will look for a better cite. ---
**Author:** ![pyromyte](https://avatars.discourse-cdn.com/v4/letter/p/d26b3c/32.png) [@pyromyte](https://boards.straightdope.com/u/pyromyte)\ **Post date:** [October 13, 2010, 2:08pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/42 "2010-10-13T14:08:40Z")
So after briefly searching around, I still do not have a great cite… As far as I can tell, the definition of a ‘hard landing’ is kind of subjective. It is somewhat defined in the commercial airliners maintenance manuals, and It varies greatly depending on model, roll, pitch, and yaw rates. But generally speaking, for a level landing, if the flight data recorder records a vertical acceleration greater than around 1.7-2.1g, then it requires the hard landing inspection. Additionally, the pilots can request the hard landing inspection if they feel it was a hard landing. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [October 13, 2010, 3:28pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/43 "2010-10-13T15:28:37Z")
> [@Kevbo](#): > > Wing tip vortices are an essential part of the mechanism by which wings produce lift. If you could eliminate them, the airplane wouldn’t fly. That sounds interesting. Can you elaborate? ---
**Author:** ![Chessic\_Sense](https://avatars.discourse-cdn.com/v4/letter/c/7c8e57/32.png) [@Chessic\_Sense](https://boards.straightdope.com/u/Chessic_Sense)\ **Post date:** [October 13, 2010, 4:52pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/44 "2010-10-13T16:52:11Z")
> [@ElvisL1ves](#): > > > [@Kevbo](#): > > > > Wing tip vortices are an essential part of the mechanism by which wings produce lift. If you could eliminate them, the airplane wouldn’t fly. > > That sounds interesting. Can you elaborate? I’m not sure if I agree with the phrasing of that one. That’s like saying “Incisions are an essential part of surgery. If you could eliminate them, surgery wouldn’t happen.” It’s true, but misleading. Vortices, like incisions, are unwanted byproducts of a process. The thing is, you can’t eliminate vortices unless you have infinitely long wings. If you _could_ get rid of the vortices (which you can’t), then there’s nothing to stop me from stipulating that lift would still be generated. The problem is that we’re in a magic fantasy land by that point, so I might as well say we all fly around on dragons and don’t need planes anyway. Here’s my understanding of it: Wings work by hitting the air at an angle, not straight on. That’s called the angle of attack. This angle knocks air down, which according to Newton’s third, makes the plane go up. It’d be like slicing lengthwise through butter, but with your blade cocked up. The butter would push the blade up, right? Well air does the same thing to make a plane fly. But since the wing is tilted up, it’s also tilted back. The lift vector doesn’t point straight up, but instead points a little bit backwards. That component is called “induced drag” since it’s part of the lift vector. That means that the more lift you generate, the more induced drag you have. So what’s this have to do with vortices? Well when air from the high-pressure bottom of the wing “leaks” around the tip to the low-pressure top, it raises the pressure above the wing. That lowers the effectiveness of the wing, especially at the tip. If your wing isn’t generating as much lift, then you have to fly with a greater angle of attack to compensate. That creates more drag, as discussed above. Vortex = less lift = higher angle of attack = more drag = more fuel = higher cost. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [October 13, 2010, 4:52pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/45 "2010-10-13T16:52:48Z")
> [@pyromyte](#): > > Additionally, the pilots can request the hard landing inspection if they feel it was a hard landing. “That wasn’t the pilot’s fault. That wasn’t the co-pilot’s fault. That was the asphalt.” ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [October 13, 2010, 4:56pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/46 "2010-10-13T16:56:31Z")
> [@ElvisL1ves](#): > > > [@Kevbo](#): > > > > Wing tip vortices are an essential part of the mechanism by which wings produce lift. If you could eliminate them, the airplane wouldn’t fly. > > That sounds interesting. Can you elaborate? Leaving out the equations: Heavier than air craft stay in the air by flinging air downward. You can fling a little bit of air quickly (short span, or a hilicopter) or a lot of air slowly (long span). When you fling some air downward with a wing, it gets replaced by the surrounding air. This upward and downward air motion manifests as a vortex behind each wing tip. Another take on it: > **[Disk Balloons: An Alternative to the Airfoil Misconception](http://amasci.com/wing/rotbal.html)** ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [October 13, 2010, 5:00pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/47 "2010-10-13T17:00:12Z")
The vortex is a \*consequence \*of lift, not a cause of it. It’s a source of inefficiency, _not_ something you need just to fly. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [October 13, 2010, 5:00pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/48 "2010-10-13T17:00:26Z")
> [@ElvisL1ves](#): > > > [@Kevbo](#): > > > > Wing tip vortices are an essential part of the mechanism by which wings produce lift. If you could eliminate them, the airplane wouldn’t fly. > > That sounds interesting. Can you elaborate? Tip vortices may be an unavoidable consequence of generating lift, but given that [winglets](http://en.wikipedia.org/wiki/Winglet) reduce the intensity of tip vortices AND result in more efficient flight, I don’t believe that tip vortices are a any kind of requirement. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [October 13, 2010, 5:12pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/49 "2010-10-13T17:12:13Z")
Good discussion. The ultralow Boeing 747 landings at St. Maarten are also worth a look: [![]( " - YouTube") ](https://www.youtube.com/watch?v=wiWJJulBLjA) [![](https://img.youtube.com/vi/_47Un8oi4sU/hqdefault.jpg "Boeing 747 - Low, Low Landing") ](https://www.youtube.com/watch?v=_47Un8oi4sU) ---
**Author:** ![Rocketeer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rocketeer/32/4437_2.png) [@Rocketeer](https://boards.straightdope.com/u/Rocketeer)\ **Post date:** [October 13, 2010, 5:49pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/50 "2010-10-13T17:49:55Z")
End of cruise: Pilot reduces engine thrust, begins descent. You sense a little “whoops” negative g for an instant, and engine noise is reduced. During descent, the flaps are extended. Whining noise, followed by increased air noise Just before landing, the landing gear are extended. Some bumping noises, much increased air noise. Landing. Thump as you hit the runway. Immediately after landing, spoilers deploy (panels on top of the wing), reducing lift significantly, allowing the airplane to settle down on the landing gear and allowing braking to be effective. Braking starts. You sense heavy decelerative G-forces, increased air noise from spoilers. About halfway down the runway, pilot deploys thrust reversers, helping to slow the airplane. You hear much more engine noise, may sense more deceleration. (An aside: Most of the slowing of the airplane is done by the brakes. Thrust reversers and aerodynamic drag from the spoilers don’t have much of an effect, compared to the brakes.) Near the end of the runway, thrust reversers become ineffective, and are stowed again. Reduced engine noise. Airplane turns off runway. Increased noise inside cabin as passengers all rise and begin to rummage in the overheads for their luggage. 😉 ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [October 13, 2010, 6:43pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/51 "2010-10-13T18:43:01Z")
> [@Chessic\_Sense](#): > > …I can tell you from experience that the brakes on a plane are nowhere near as effective as aerodynamic brakes. I can stop my Cessna in two ways- stepping on the brakes or pulling up the elevator. The former stops you eventually. The latter stops you right away… > [@Rocketeer](#): > > …Most of the slowing of the airplane is done by the brakes. Thrust reversers and aerodynamic drag from the spoilers don’t have much of an effect, compared to the brakes… Are you contradicting each other, or am I misreading this? ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 13, 2010, 7:42pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/52 "2010-10-13T19:42:26Z")
> [@Elendil\_s\_Heir](#): > > Are you contradicting each other, or am I misreading this? ISTM that **Rocketeer** is talking about commercial jets, or ‘heavies’, and **Chessic Sense** is talking about General Aviation aircraft. ‘Heavies’ do seem to use a lot of brake. How much of the deceleration is from the reverse thrust and how much is from the brakes, I can’t tell you. When I was flying fixed-wing, I generally flew one of dad’s planes. I remember (before I got my license) hearing him talking about how much the brakes cost. So when I started flying, I habitually came in with 40° of flaps and set it right on the numbers. Never had to use the brakes. Actually, since it was in the ever-windy Mojave Desert, sometimes I had to add power to get to the turn-off. (It wasn’t entirely that I was trying to save dad’s brakes, of course. I just really like making that kind of landing.) ---
**Author:** ![Huerta88](https://avatars.discourse-cdn.com/v4/letter/h/82dd89/32.png) [@Huerta88](https://boards.straightdope.com/u/Huerta88)\ **Post date:** [October 13, 2010, 7:49pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/53 "2010-10-13T19:49:32Z")
> [@Whack-a-Mole](#): > > > [@Chessic\_Sense](#): > > > > If you want to overcome your fear of flying, just consider what happens when an engine quits. The plane doesn’t become a rock. It becomes a glider. At 4,000 feet, a Boeing 747 can glide 11.6 miles. That’s a lot of space for such a low altitude. If the landing gear doesn’t open, you can still land perfectly safely on the belly of the aircraft. Sure, the plane is ruined, but you’re still alive. > > Must post link to the [Gimli Glider story](http://www.wadenelson.com/gimli.html). A 767 rather than a 747 and not exactly a belly landing (no front nose gear) but close enough. Great story (and a happy ending…not giving it away since the pic in the link tells that much). > > Good, short read. If you haven’t (whoever is reading this) give it a look. Though an 11.6 mile glide is not all that much at all to maneuver in. Here’s another scary but successful one. > **[Air Transat Flight 236](https://en.wikipedia.org/wiki/Air_Transat_Flight_236)** > > Air Transat Flight 236 was a transatlantic flight bound for Lisbon, Portugal, from Toronto, Canada, that lost all engine power while flying over the Atlantic Ocean in the dark on August 24, 2001. The Airbus A330 ran out of fuel because of a fuel leak caused by improper maintenance. Captain Robert Piché, 48, and First Officer Dirk DeJager, 28, glided the plane to a successful emergency landing in the Azores, saving the lives of all 306 people (293 passengers and 13 crew) on board. This was also... The Air Transat guys were losing 2,000 ft./min. altitude after final engine flameout. Although they still had enough altitude to spare that they had to fly some circles at the Azores to get down to landing altitude. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [October 13, 2010, 9:49pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/54 "2010-10-13T21:49:58Z")
**Chessic Sense** said: > [@](#): > > Yep. It’s wing vortices. There’s a high pressure zone below the wing, right? And a low pressure one above it? Well, air at the end of the wing tries to wrap around the tip of the wing. So instead of flowing off the trailing edge, it goes off at an angle. Since there’s less air on the bottom near the tip, air on the bottom near the middle moves to fill that void. This chain of effect happens all along the bottom of the wing. So you get a flow from the fuselage to the wingtip. > > Then, on top of the wing, there’s more air coming up from the bottom at the tip, so that wing tip air is pushed toward the middle of the wing, and that pushes air in the middle toward the fuselage, and so on. That makes a flow from the tip to the fuselag, the opposite of what’s going on underneath the wing. So you get this spiral that develops. That’s a wingtip vortex. Thank you. I’ve never given this much consideration, but that explanation makes it very clear and immediately a duh moment for consequences of the pressure differential. **Chessic Sense** said: > [@](#): > > The vortices are part of induced drag, which is drag caused by the production of lift. I honestly don’t have a good handle on how that’s different from aerodynamic drag, but you can read about it [here](http://en.wikipedia.org/wiki/Wingtip_vortices). I chased my way through a string of wikipedia pages. > **[Lift-induced drag](https://en.wikipedia.org/wiki/Lift-induced_drag)** > > Lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, in aerodynamics, is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars with airfoil wings that redirect air to cause a downforce. It is symbolized as > > > > > D > > i > > > > > {\\textstyle D\_... Aerodynamic drag is drag due to the cross section of the object, skin friction, and interference drag, which is an effect in transonic flight i.e. crossing from below sonic to supersonic speeds. Induced drag is caused by additional airflow not from airspeed. The wing has an airflow from airspeed that runs from front to back across the top of the wing. The wingtip vortex pulls air across the top of the wing, which (a) adds air pressure, and (b) changes the airflow direction slightly (vector combination). More pressure above the wing means less pressure difference, which means in order to keep the same lift, the plane has to increase angle of attack. Increasing angle of attack puts more wing profile into cross section, increasing drag. That increased drag is the “induced drag”, induced by the act of how the cross flow affects wing performance. > [@](#): > > The point to remember is that the more the airstream flows sideways, the less it’s doing its job of lifting the airplane. Less lift means a higher angle of attack, which means more drag. The airflow moving sideways is work being done by the airplane, and therefore fuel being spent by the engines. That work is being done in a manner that does reduces lift and increases drag, ergo it is inefficient. Remove the vortex and that work is spent on lift, not drag. **Whack-a-Mole** said: > [@](#): > > While not exactly common yet [crushable concrete](http://www.flightglobal.com/blogs/as-the-croft-flies/CRW_CRJ_overrun.JPG) (do not know its proper name) is being deployed at more airports all the time for a plane that overruns the end of the runway. Basically the weight of the plane causes it to sink into the special concrete making it akin to the plane driving through sand which slows it down very fast if all else fails to stop you. Aerated concrete. [Autoclaved aerated concrete - Wikipedia](http://en.wikipedia.org/wiki/Autoclaved_aerated_concrete) The chemistry makes hydrogen bubbles in the material. That and lighter weight aggregate make it lighter and crushable. **Kevbo** said: > [@](#): > > When you fling some air downward with a wing, it gets replaced by the surrounding air. This upward and downward air motion manifests as a vortex behind each wing tip. > > Another take on it: > [Disk Balloons: An Alternative to the Airfoil Misconception](http://amasci.com/wing/rotbal.html) There’s no reason the surrounding air must come from the air below the wing. In theory, one could eliminate air wrapping around the wingtip, thus preventing vortex formation, but still deflect air by the pressure differential from top and bottom of wing. In practice, eliminating wing wraparound is difficult. Reduction is possible, but reducing it is a trade off in wingspan or winglet size/weight vs performance improvement. As a practical matter, the air wants to wrap around the wing rather than move in from above the plane. That’s because the air under the wing is higher pressure than the air above the plane. That air pressure wants to equalize. **Chessic Sense** said: > [@](#): > > I’m not sure if I agree with the phrasing of that one. That’s like saying “Incisions are an essential part of surgery. If you could eliminate them, surgery wouldn’t happen.” It’s true, but misleading. A better analogy is “Pain is an essential part of surgery.” Pain is a natural outcome of cutting tissue, and tissue trying to heal. It isn’t the point of surgery, and theoretically isn’t required, but eliminating it is difficult because of the inherent nature of pain. Meds only go so far. Same thing with winglets etc. We can reduce wingtip vortices, and vortices aren’t required for flight, but are a natural consequence of the mechanism of flight and are nearly impossible to completely eliminate because of that. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [October 13, 2010, 10:59pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/55 "2010-10-13T22:59:36Z")
Leaving San Diego a couple weeks ago, our pilot told us we’d be delayed because they had re-configured the runways and now we were too heavy to take off with the wind behind us. He said to wait for further word from him. My question was, don’t they always take off _into_ the wind anyway? At least when they can? Or at least with a cross wind? ---
**Author:** ![mnemosyne](https://avatars.discourse-cdn.com/v4/letter/m/c4cdca/32.png) [@mnemosyne](https://boards.straightdope.com/u/mnemosyne)\ **Post date:** [October 13, 2010, 11:16pm UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/56 "2010-10-13T23:16:12Z")
> [@Machine\_Elf](#): > > I’m pretty sure the whiny sound of these engines during takeoff is a characteristic of [high bypass ratio turbofan engines.](http://en.wikipedia.org/wiki/Turbofan) These are engines in which the fan disc (visible at the front of the engine) moves a lot of extra air through the nacelle, but _outside_ of the engine (in addition to cramming the usual amount of air directly into the engine itself). Not just the A-320, many other large planes (Boeing 747 and 757 come immediately to mind) also use high bypass ratio turbofans because they are quieter for a given level of thrust than other engines. > > I believe the whine is related to operating the engine at a high power setting (sucking a lot of air through it) while the aircraft is moving forward at a relatively low speed, typically 200-300 MPH during the early part of the ascent. As the plane approaches cruise speed (typically 500-600 MPH), the forward speed of the aircraft is helping to stuff air into the engines, resulting in a different angle of impingement of the air on the blades of those big fan discs, and causing the whining noise to fade away.. I know what you mean, and don’t disagree with the physics of what you’ve said, but the fact is, the A320 has one engine type that has a whine that is somewhat more distinct than the others, so much so that it is specifically recorded and simulated for that aircraft type in full-flight sims. The absence of the whine makes the test pilots antsy. > [@EmAnJ](#): > > > [@mnemosyne](#): > > > > Hard landings are reportable events in Canada, and there is no report of one so far in the [CADORS](http://wwwapps.tc.gc.ca/Saf-Sec-Sur/2/cadors-screaq/m.aspx?lang=eng)for landings at Calgary this weekend. > > The hard landing was on the flight to Las Vegas. Is there something similar for the US? Yes, but I’ve always found it to be less organized and useful. I think [this](http://www.faa.gov/data_research/accident_incident/preliminary_data/)is it (though I seem to remember another database from the last time I looked!). I didn’t see anything for this past weekend about a hard landing in Las Vegas, but I don’t know the details of your flight. Unofficial and less thorough, [avherald.com](http://avherald.com) also doesn’t report a hard landing. > [@pyromyte](#): > > . I am guessing a hard landing would be classified as an _incident_, but I don’t know. Assuming the FAA uses only the I[CAO Annex 13](http://www.scribd.com/doc/10862579/Icao-Annex-13-9th-edition) definitions (most countries add additional criteria), a hard landing is an incident requiring a hard landing structural check. If the aircraft is substantially damaged, it may be classified as a Serious Incident or an Accident. An accident is defined as: > [@](#): > > a) a person is fatally or seriously injured as a result of: > — being in the aircraft, or > — direct contact with any part of the aircraft, including > parts which have become detached from the aircraft, > or > — direct exposure to jet blast, > except when the injuries are from natural causes, self- > inflicted or inflicted by other persons, or when the > injuries are to stowaways hiding outside the areas > normally available to the passengers and crew; or > b) the aircraft sustains damage or structural failure which: > — adversely affects the structural strength, performance > or flight characteristics of the aircraft, and > — would normally require major repair or replacement > of the affected component, > except for engine failure or damage, when the damage is > limited to the engine, its cowlings or accessories; or for > damage limited to propellers, wing tips, antennas, tires, > brakes, fairings, small dents or puncture holes in the > aircraft skin; or > c) the aircraft is missing or is completely inaccessible. Most countries have additional regulations about what is a reportable incident to the airline and to the aviation authority for trend/SMS/informational purposes. ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [October 14, 2010, 12:43am UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/57 "2010-10-14T00:43:55Z")
> [@CC](#): > > Leaving San Diego a couple weeks ago, our pilot told us we’d be delayed because they had re-configured the runways and now we were too heavy to take off with the wind behind us. He said to wait for further word from him. My question was, don’t they always take off _into_ the wind anyway? At least when they can? Or at least with a cross wind? Maybe they got instructions to taxi to one end of the runway and then the wind changed directions. I was practicing touch-and-gos once when that happened. The tower told me to land and do a long roll-out to the far end of the runway, then turn around and take off again. ---
**Author:** ![ladeda](https://avatars.discourse-cdn.com/v4/letter/l/bbe5ce/32.png) [@ladeda](https://boards.straightdope.com/u/ladeda)\ **Post date:** [October 14, 2010, 1:21am UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/58 "2010-10-14T01:21:46Z")
> [@CC](#): > > Leaving San Diego a couple weeks ago, our pilot told us we’d be delayed because they had re-configured the runways and now we were too heavy to take off with the wind behind us. He said to wait for further word from him. My question was, don’t they always take off _into_ the wind anyway? At least when they can? Or at least with a cross wind? SAN has one runway: 9/27. Was it foggy there? The preferred runway in SAN is 27 for arrivals and departures. However, if the visibility was low they might have switched to landing on runway 9 which has lower visibility minimums than runway 27; that is, they can land at a lower visibility than if they were landing on 27. Switching to landing on runway 9 would also require departing on 9 even if there was a tailwind unless the tower approved an opposite runway departure (27) but that would most likely result in a departure delays waiting for a break in the arriving traffic. There are lower maximum takeoff weights departing on 9 anyway due to the obstacle near the end (parking garage I believe.) ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [October 14, 2010, 1:47am UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/59 "2010-10-14T01:47:11Z")
Nope. No fog. 11:30 am. Plenty clear by then. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [October 14, 2010, 2:31am UTC](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909/60 "2010-10-14T02:31:21Z")
> [@CC](#): > > Leaving San Diego a couple weeks ago, our pilot told us we’d be delayed because they had re-configured the runways and now we were too heavy to take off with the wind behind us. He said to wait for further word from him. My question was, don’t they always take off _into_ the wind anyway? At least when they can? Or at least with a cross wind? No they don’t always take-off into wind. There are many things that go into the decision to use a particular runway. In some places that have several airports near each other, a change in the duty runway at one airport means the other nearby airports have to change their duty runway as well so the traffic flow works in the local airspace. The upshot of this is that sometimes an airport is operating off a non-preferred runway. There are also occasions when the maximum weight taking off from one runway with a tail wind will be higher than the maximum weight allowed taking off into wind. This would be due to terrain or other obstacles infringing the take-off path on one runway only. This obviously wasn’t the case for you though. [Previous page](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909.md?page=2) [Next page](https://boards.straightdope.com/t/what-is-happening-when-the-airplane-lands/556909.md?page=4)