# Flying a Jetliner into a Tunnel **URL:** \ **Category:** Factual Questions\ **Created:** [January 15, 2009, 8:00am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401 "2009-01-15T08:00:21Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [January 17, 2009, 1:51am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/61 "2009-01-17T01:51:59Z")
> [@Lobohan](#): > > They will. What does that have to do with landing planes in dangerous tunnels? It _doesn’t_. You’ll notice **I** wasn’t the one who brought the subject about carbon footprints up. > [@](#): > > Utterly meaningless. Future airports will be smaller and much more efficient due to technology. I see planes landing every two minutes and taking off like a swiss clock because of automated air traffic control and piloting. None of that necessitates building expensive and useless dangerous underground tunnels. You’ve made zero case for it, you just keep repeating that people would get used to them. There’s still a _minimum_ size for an airport, even if you give something like an A380 VTOL capability. There’s also a minimum amount of distance planes will have to remain a part because of things like jet wash. Not to mention, you’ve got have some place to put the plane while passengers are loaded and unloaded from the plane. > [@](#): > > There is zero benefit to underground tunnels. Actually, there _are_ benefits to underground tunnels, otherwise we wouldn’t use them for things like subways. I presume you’d have no problem with putting the _airport_ buildings underground, while leaving the runways on the surface? > [@](#): > > There are manifold reasons against it. Just because you think it would be nifty doesn’t make it likely. What I think of it is immaterial, and I’m not interested in reasons why people wouldn’t **like** it, but what **technological** reasons there might be against doing it. So far, the cost of digging the holes, and the need to properly vent the tunnels seem to be the biggest issues. The computer power to control a plane in such a situation will come about, even if we _never_ do it. > [@](#): > > Let me say it again. There are no benefits to dangerous underground landing strips. Besides freeing up large stretches of land. > [@](#): > > It’s more expensive in terms of engineering and set up and more dangerous in terms of landing a jet. Just because it’s neat doesn’t mean it’s smart. One could say the same thing about VTOL aircraft, yet we have them, and the number of them looks to be increasing. ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [January 17, 2009, 1:55am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/62 "2009-01-17T01:55:48Z")
As for reducing environmental damage… even if you end up with a lovely landscape up top where there used to be a large airfield before I’d like to see how that compares to the overall environmental impact of digging a frikkin’ huge hole in the first place, building more complex, heavier and expensive infrasructure underground and the higher operating costs of the subterranean airport. To begin with, the monumental energy needed to dig out the ground; that energy comes from somewhere and it’s more likely than not that the generation of that energy has an impact on the environment. Secondly, most airports I’ve seen are for the most part light structures. For example the Suvarnabhumi airport here in Bangkok is a metal lattice structure with canvas roofs and glass walls. If you’d had to build such a terminal underground it would have to be a bunker, using thousands of tons of more material to support the weight of the ground above and the pressure from the soil on the sides. Also the runways and taxi ways at the very least will need 4 times more concrete, tarmac, two walls on the sides and a roof. Not to talk of things like hangars that are very lightly built, usually just very large corrugated metal boxes. You would be replacing light, relatively economic structures with much heavier and expensive ones. That would also increase the environmental impact since all that extra steel, concrete and whatnot would have to be produced. Thirdly, the airport wouldn’t be able to use daylight and would depend on electric lighting 24/7, again at least doubling the energy needs that will have an impact on the environment. Just WAGing here, but I’d bet building such an airport would have 20 times the overall environmental impact of a normal airport and be at least 3 times more expensive to operate. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [January 17, 2009, 1:56am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/63 "2009-01-17T01:56:46Z")
> [@Mangetout](#): > > Like the folks who knew anything about trains thinking it was a stupid idea to exceed 30mph? More like human anatomy. It was thought that we’d be unable to _breath_ at those speeds. > [@](#): > > You can’t generalise from wild ideas in the past that either succeeded or failed. This idea will succeed or fail _on its merits_, not because people were wrong or right about something else, some other time. True, but one shouldn’t automatically agree with statements of “People will never want something like that!” or “We’ll never need anything like that!” as quite often, it turns out that people _do._ ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [January 17, 2009, 2:01am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/64 "2009-01-17T02:01:28Z")
If your robot autopilot of 2059 is so brilliant, why assume that you need a runway to land on? Just have the plane flare, stall, and drop onto a perch like a songbird. ---
**Author:** ![Lobohan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lobohan/32/79_2.png) [@Lobohan](https://boards.straightdope.com/u/Lobohan)\ **Post date:** [January 17, 2009, 2:10am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/65 "2009-01-17T02:10:57Z")
> [@brossa](#): > > If your robot autopilot of 2059 is so brilliant, why assume that you need a runway to land on? Just have the plane flare, stall, and drop onto a perch like a songbird. That would only make sense if the perch is a quarter mile underground in a giant tunnel. 😃 ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [January 17, 2009, 2:12am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/66 "2009-01-17T02:12:49Z")
> [@Ale](#): > > As for reducing environmental damage… even if you end up with a lovely landscape up top where there used to be a large airfield before I’d like to see how that compares to the overall environmental impact of digging a frikkin’ huge hole in the first place, building more complex, heavier and expensive infrasructure underground and the higher operating costs of the subterranean airport. > > To begin with, the monumental energy needed to dig out the ground; that energy comes from somewhere and it’s more likely than not that the generation of that energy has an impact on the environment. True. One can “clean” the energy up using electricity generated via solar, hydro, or some other green source, but that’s a maybe. > [@](#): > > Secondly, most airports I’ve seen are for the most part light structures. For example the Suvarnabhumi airport here in Bangkok is a metal lattice structure with canvas roofs and glass walls. If you’d had to build such a terminal underground it would have to be a bunker, using thousands of tons of more material to support the weight of the ground above and the pressure from the soil on the sides. > Also the runways and taxi ways at the very least will need 4 times more concrete, tarmac, two walls on the sides and a roof. That would depend upon what the ground in the particular area is like. If its soft material, then you’re going to have to go with concrete, but with rock, and certain types of soil, you’re not. Also, in the US and most other developed nations, you wouldn’t be able to get away with building something out of canvas. > [@](#): > > Not to talk of things like hangars that are very lightly built, usually just very large corrugated metal boxes. True. > [@](#): > > You would be replacing light, relatively economic structures with much heavier and expensive ones. That would also increase the environmental impact since all that extra steel, concrete and whatnot would have to be produced. Some of the figures I’ve seen for underground buildings have the costs to construct them as being something like 30% higher (depending upon on the type of _above_ ground building they were replacing), with those costs being quickly offset by the _energy savings_ from not having to maintain the climate in the building via conventional HVAC systems. > [@](#): > > Thirdly, the airport wouldn’t be able to use daylight and would depend on electric lighting 24/7, again at least doubling the energy needs that will have an impact on the environment. Two words: [Tubular skylights](http://www.tubularskylight.com/). I’ve seen systems designed to “pipe” natural sunlight into deeply buried structures. > [@](#): > > Just WAGing here, but I’d bet building such an airport would have 20 times the overall environmental impact of a normal airport and be at least 3 times more expensive to operate. It might well, indeed. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [January 17, 2009, 2:14am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/67 "2009-01-17T02:14:07Z")
> [@brossa](#): > > If your robot autopilot of 2059 is so brilliant, why assume that you need a runway to land on? Just have the plane flare, stall, and drop onto a perch like a songbird. But as someone pointed out above VTOL capability is “too heavy” and is only used for a short period of the flight to ever be considered to be practical. ---
**Author:** ![Lobohan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lobohan/32/79_2.png) [@Lobohan](https://boards.straightdope.com/u/Lobohan)\ **Post date:** [January 17, 2009, 2:22am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/68 "2009-01-17T02:22:28Z")
> [@Tuckerfan](#): > > But as someone pointed out above VTOL capability is “too heavy” and is only used for a short period of the flight to ever be considered to be practical. He’s not assuming VTOL in the modern sense, I think he’s thinking these future autopilots that care not for flying into concrete walls, could swoop up, thrust down and land perfectly safe, butt first. If you were referring to my thing about VTOL, I didn’t say it would be impractical. I said that a plane without VTOL would outperform it based on fuel. I’m sure they’ll have a use, but economically hauling people is unlikely. But we aren’t talking about VTOL in this thread, because VTOLs don’t need runways. So no need for the ridiculous tunnels to land the planes in. ---
**Author:** ![DanBlather](https://avatars.discourse-cdn.com/v4/letter/d/f4b2a3/32.png) [@DanBlather](https://boards.straightdope.com/u/DanBlather)\ **Post date:** [January 17, 2009, 2:43am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/69 "2009-01-17T02:43:14Z")
> [@Ale](#): > > Well, what do you know?. I went out to refresh my memory on the Akagi and it turns out that it didn’t have two decks for take off… it had three. :eek: > > [Here you can see the arrangement on a plastic model of the ship](http://solomaquetas.com/forum/index.php?showtopic=7123) Those pilots would have to have been suicidal! ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [January 17, 2009, 2:52am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/70 "2009-01-17T02:52:33Z")
> [@Lobohan](#): > > He’s not assuming VTOL in the modern sense, I think he’s thinking these future autopilots that care not for flying into concrete walls, could swoop up, thrust down and land perfectly safe, butt first. > > If you were referring to my thing about VTOL, I didn’t say it would be impractical. I said that a plane without VTOL would outperform it based on fuel. I’m sure they’ll have a use, but economically hauling people is unlikely. > > But we aren’t talking about VTOL in this thread, because VTOLs don’t need runways. So no need for the ridiculous tunnels to land the planes in. But we _are_ talking about VTOLs in this thread, along with many other things. Here’s a question: How much space does a VTOL aircraft take up as its landing? I’m not talking _just_ about the size of the plane, but also the various air currents created by the thrusters. Can two VTOL aircraft land at the same time with less than 10 feet between their wingtips? How close can something be on the ground to the planes and **not** be drastically affected by the jetwash? ---
**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:** [January 17, 2009, 7:08am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/71 "2009-01-17T07:08:40Z")
> [@Tuckerfan](#): > > But we _are_ talking about VTOLs in this thread, along with many other things. > > Here’s a question: How much space does a VTOL aircraft take up as its landing? I’m not talking _just_ about the size of the plane, but also the various air currents created by the thrusters. Can two VTOL aircraft land at the same time with less than 10 feet between their wingtips? How close can something be on the ground to the planes and **not** be drastically affected by the jetwash? A look at military history would show that true VTOL has extremely limited uses. This is tried technology that fills a niche role and I personally can’t see it being viable for large passenger aircraft, but aside from that, lets have a look at your robot that flies the aeroplane into a tunnel. I’m not sure who used the term “robot” first in this thread, or why, but we already have these robots and we call them autopilots. There’s one thing a computer is good at, giving a specific output in response to a given input. But there’s much more to being a pilot than that, being a pilot requires _judgement_, for no two situations are ever exactly the same and it is not possible to account for every problem that may arise. As an example, I fly an aircraft fitted with TCAS which is designed to help avoid midair collisions. Without boring you with the details too much, a TCAS normally consists of a display of surrounding air traffic and gives aural and visual warnings if a collision is likely as well as avoidance advice. The avoidance advice is in the form of a directive to climb, descend, or keep doing what you’re doing, and if the other aircraft has TCAS they will get a complementary command. Now, for obvious reasons, DESCEND commands are inhibited below a certain altitude. Recently I was on final approach to land, descending through about 200 feet, and was given a DESCEND command by the TCAS, I was given another DESCEND command a little later as we were flaring to land. Do you think I followed the instruction? Of course not, it would’ve killed us. Would your robot have followed the instruction? Well it will have been programmed not to follow TCAS commands that put the aircraft into danger but then the TCAS had already been programmed not to _give_ a command that would put us into danger. If the fault that caused the TCAS to give a bad command had also affected your hypothetical robot then it would have driven the aeroplane into the ground and killed all on board. As it happens the fault was unrelated to the TCAS. It was a problem with the radar altimeter and it could easily have affected more than one system that relied on it. Another example is the Qantas A330 that recently injured several people when its automatic flight systems went haywire. It had redundancy and protections that should have meant that a faulty computer was ignored, for reasons not yet made public the system didn’t work as expected and the results were pretty unpleasant. As you’ve said, a robot doesn’t take time to react, it can give the programmed response to a given warning immediately. The problem is the programmed response may not be the appropriate one for the situation and there are only a couple of people with a chance of having anything like a full grasp of the situation, the human pilots siting up the front. Although they have slow response times, fatigued brains, and imperfect sensory equipment, they are also much more capable at giving an appropriate response to a new situation, one that the aircraft designers hadn’t thought or had considered too unlikely to cater for. The problems posed by landing and taking off into a tunnel are not fixed by using automation. Automation doesn’t have the weaknesses humans have, but it brings its own weaknesses. Now, here are some things to consider for your tunnel idea. Different aircraft have different performance and will use varying amounts of runway to take off. The solution would be to have them fly low until they clear the tunnel. The problem then is that flying at high speed and low altitude has high levels of risk. There are pages of airline procedures written to specifically prevent aircraft spending excessive time close to the ground. As mentioned by others, there will be times where the aircraft has to conduct a missed approach, regardless of who or what is flying it. You won’t be able to do that from a tunnel. Also you need to consider what happens when systems fail. What happens when an engine fails after take-off? At the moment it doesn’t matter if you get a bit off course, in a tunnel it would be deadly. Unlike a lot of other inventions that may have been thought impossible but have since become a reality, landing and taking off from tunnels just doesn’t seem like a good idea. It would take huge advances in technology for a very minimal benefit. Much easier and safer to just restrict the number of aircraft operating. It would also be safer and easier to just have gigantic fans set up that create an artificial 150knot wind so the aircraft can land and take-off with no ground speed, a wind-treadmill I suppose, heck, why not call it a “windmill?” ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [January 17, 2009, 7:29am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/72 "2009-01-17T07:29:04Z")
Good points, but fly-by-wire systems are prone to glitches (“prone” in the sense that we’ve yet to come up with a 100% foolproof system), and we still use them, even though some of those glitches can have fatal, or near fatal consequences. As for the need for the ability to “touch and go,” one would presume that a tunnel open at both ends of a large enough diameter would allow this, no? ---
**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:** [January 17, 2009, 7:48am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/73 "2009-01-17T07:48:36Z")
One big thing aeroplanes have going for them is that there is a lot of space and usually a lot of time available to deal with problems. Fly-by-wire doesn’t seem to have many problems at all, but when there is a problem, such as with the Qantas jet, the worst that happened was that the aircraft deviated from the flight path and a few people got hurt. When you confine the flight path with a tunnel then you take away all the physical margins the aircraft has. All you are left with is the ability of the automatics to fly the plane along a defined course. We’ve been trying to get that right for 100 years and still have a long way to go. On missed approaches, you need to be able to do a missed approach (not a “touch and go” which is where you land then take-off and is normally confined to training in light aircraft) from any point in the approach. The only way to accommodate a missed approach would be to take the top off the tunnel, which defeats the purpose. By limiting the ability to do a missed approach you’re taking away the best and most widely used tool for getting out of trouble. ---
**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:** [January 17, 2009, 7:55am UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/74 "2009-01-17T07:55:09Z")
It’s worth considering that people manage to crash trains. ---
**Author:** ![Jake](https://avatars.discourse-cdn.com/v4/letter/j/f475e1/32.png) [@Jake](https://boards.straightdope.com/u/Jake)\ **Post date:** [January 17, 2009, 4:05pm UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/75 "2009-01-17T16:05:14Z")
> [@flyboy](#): > > This is pretty silly speculation. There is no way this’ll ever happen. Aside from everything already mentioned, you simply cannot shoot an approach down to the minimums, break out at the last second, make corrections, and zoom right on into a tunnel opening. Firstly, there’s no way to make corrections due to crosswinds and centerline adjustments. Secondly, you’d have to raise the landing mins (the height of the cloud deck above the ground) to give aircraft more time to make a precise path to the opening. Aircraft need a nice long, wide, open-field runway to make these corrections. Ever been on an airplane that’s floated for a bit down the runway before setting down? How’s that going to work with a tunnel opening? > > This isn’t even taking into account the empty aircraft and soon-to-be bankrupt airlines operating out of that airport. I mean, I wouldn’t fly on that plane. Would you? **flyboy** , very informitave, thank you. Have you ever flown a commercial jetlliner? ---
**Author:** ![flyboy](https://avatars.discourse-cdn.com/v4/letter/f/4da419/32.png) [@flyboy](https://boards.straightdope.com/u/flyboy)\ **Post date:** [January 17, 2009, 5:48pm UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/76 "2009-01-17T17:48:07Z")
Thanks! No, haven’t flown a commercial jet like that, just a private pilot and 14 years flying (3000+ hours) on naval aircraft as a Naval Flight Officer. I’ve flown in sandstorms and snowy, foggy weather down to (and sometimes below) the mins. I’ve flown with in-flight emergencies, sick crewmembers, low fuel, you name it. Having room to play with before touchdown is critical when conditions aren’t ideal and you _have_ to get the plane on deck. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 17, 2009, 10:28pm UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/77 "2009-01-17T22:28:47Z")
What was the reason for tunnels again? So you can use the same land footprint for something else at surface level? Why would it ever make sense to do it that way? You’d keep the runway at surface level and build the other stuff underground. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [January 17, 2009, 10:31pm UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/78 "2009-01-17T22:31:26Z")
> [@Mangetout](#): > > What was the reason for tunnels again? So you can use the same land footprint for something else at surface level? Why would it ever make sense to do it that way? You’d keep the runway at surface level and build the other stuff underground. You wanna live underground? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 17, 2009, 10:49pm UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/79 "2009-01-17T22:49:55Z")
No, but I don’t want to live on top of an airport either. So it’s a wash. ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [January 17, 2009, 11:39pm UTC](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401/80 "2009-01-17T23:39:56Z")
> [@Tuckerfan](#): > > But as someone pointed out above VTOL capability is “too heavy” and is only used for a short period of the flight to ever be considered to be practical. I’m saying that an autopilot/plane that is sophisticated enough to fly into a hole in the ground in all weather, compensating for sudden, massive differences in aircraft handling due to ground effect, cessation of headwind/crosswind, etc. etc. etc., is sophisticated enough to stall and drop gently onto a tiny landing platform without any fancy VTOL equipment. Build the perch at the top of a skyscraper and you could just shove the planes over the edge to launch them. If the skyscraper isn’t high enough you could just dig out a curved tunnel of the right shape so the plane could pull out of the dive while it was still underground! [Previous page](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401.md?page=3) [Next page](https://boards.straightdope.com/t/flying-a-jetliner-into-a-tunnel/481401.md?page=5)