The Soviets equipped most of their fighter aircraft with moveable guards to prevent debris from being sucked into jet engines on takeoff. Such guards would have saved the lives of the passengers on the Concorde that crashed, as well as prevented the crash of the US Airways jet yesterday. While debris on the runway getting sucked into the engines is an uncommon occurance, bird strikes are not. Commercial jet engines are designed to digest small birds with no real problems, but things like Canadian geese aren’t protected against. Even in commercial aircraft, safety tradeoffs are made.
[nitpick] Nothing was ingested through the intake of the Concorde that crashed. A strip of metal debris punctured one of the tires which then exploded. Shrapnel from the tire then punctured the underside of the fuel tank, which then led to the fire and crash. [/nitpick]
Accepting the fact there will be several thousand birdstrike incidents involving airliners each year – a tiny fraction of annual traffic, only a small fraction of which then result in accidents – is a safety tradeoff.
Flying an airplane inside a tunnel is patently unsafe.
That’s the difference.
[nitpick]
The Concorde crashed due to tire pieces rupturing the fuel tank under the wing, not being ingested by the engines, AFAIK.
[/nitpick]
Flying is patently unsafe. There is always the risk of something going wrong, and you cannot simply pull over and fix the problem. We work to make dangerous things like flying safer. Flying a jet into a tunnel (IIRC, the Germans were working on cave based aircraft during WWII because that was the only way they could shield them from Allied bombings) is beyond our current technology.
I think others have been getting at this, but I want to lay it out plainly:
The only reason to put the runway underground is so you can put something else above the ground, right?
So why not just put the something-else underground? Is there something you need to build that has a better reason for being on the surface than a runway has?
Trees don’t grow very well underground. I’m not kidding when I say environmental laws are going to more stricter. We’re rapidly finding out that even our best efforts to have a minimal impact on the environment aren’t enough. As the rest of the world begins to reach First World standards, you’re going to be putting even more stresses on the environment (cutting the environmental impact of a First World person by 20% doesn’t do you much good if there’s now 30% more people enjoying a First World lifestyle), and you’re going to wind up with the situation of needing to put an airport someplace, and there’s no good place to put it. Stick it too far away from the city, and even with high speed mass transit, you don’t gain anything as far as travel times go. Put it too close to the city, and you’ve got tens of thousands (if not more) people you have to move and relocate.
Assuming, for the moment, that the decision would be made to buy up large sections of land for an airport, and relocate all the people who lived in that area somewhere else (I doubt if many of them would want to live under the airport), you’ve got to find housing for them (that they can afford, don’t forget that pushing people out of one area will driving housing costs up in another), and you’ve always got people who, like what is presently going on at Heathrow, try to find as many ways possible to stop the deal. At some point, what first seemed like an idea out of left field, becomes the most practical option. Would the Wright brothers ever have imagined that their plane at Kitty Hawk would one day lead to aircraft carriers, and spaceships riding “piggyback” on airplanes?
How about you have a giant robotic grabber that moves very fast along a track, to match speed with the descending plane, and then grabs it and pulls it down into a tunnel?
Didn’t they do that on Thunderbirds?
This is becoming semantic, but that’s ok with me 
Having an element of risk is not the same thing as being unsafe. For instance, investment is risky, whereas using your retirement savings for margin trading is unsafe. Sex is risky, and unprotected sex with strangers is unsafe.
More on topic, driving is risky. In fact, it is far more likely to result in death or injury than is flying on a jetliner. But driving is an everyday activity that most people I know don’t think of as dangerous or “patently unsafe.” However, I do think a lot of people would consider driving a car across a ravine on a narrow bridge with no guardrails on a windy day at high speed unsafe, because it’s likely to turn out badly. It would take skill, attention, and good fortune just to make it across safely.
That’s a decent analog for flying in a tunnel. Perfect execution and conditions are required to avoid an accident. Any deviation from the normal flight path, or any mechanical failure while flying in an enclosed space would result in a catastrophic accident instead of an insignificant incident or a potentially managable emergency.
There is no good reason to fly an airplane through a tunnel. There are lots of good reasons not to do it.
By contrast, there are many good reasons to fly, and the reasons not to fly are mostly economic and environmental, not related to safety. Any person who thinks commercial flying is unsafe should also not drive or travel by any other modern means. In fact, they should probably stay home.
A better solution to the problem of no space for airport expansions:
Every argument you’re making was no doubt made by someone in relation to things like rail travel, cars, aircraft, and spaceflight. At one time it was thought that humans wouldn’t be able to survive going faster than thirty five miles an hour! Funny how things change.
That’s assuming that you’ve got a large body of water nearby to put that in. What about places like Las Vegas (or more likely, Beijing)?
So let’s boil it down here.
For Underground Tunnels:
It allows the above ground to be used for other stuff, like growing trees?!?
It necessitates awesome robot pilots and cool stuff like real time weather modeling and high tech doppler ladar.
**
Against Underground Tunnels:**
It’s fucking dangerous for no reason.
It’s fucking expensive for no reason.
The above ground areas can be used for things besides growing trees, as I mentioned. And planes are going to be getting all the fancy electronics anyways. Wind shear is a threat to planes at every point they’re off the ground, and as more and more stuff is crammed on to planes (Ryan Air’s planes are flying casinos, Virgin has inflight wifi, lots of planes now have TVs in seatbacks), pilots are going to need more and more sophisticated instrumentation to keep track of everything.
Now, yes. In fifty years, it may be another story. How many people were worried about global warming fifty years ago? How many people were worried about air pollution? Overpopulation? Overfishing? There were a few people talking about such things, but most folks would have dismissed them as utter nonsense.
Still not seeing it, Tuck. If environmental regulations are going to be so tight, it’s likely that air travel will be restricted, as it is highly inefficient, or humongous planes will be used to lower the carbon footprint. If space is a premium, such as at Heathrow, expansion can happen in outlying areas, and high-speed rail will be used to complete the journey. And how many people do you think would actually want to land in a tunnel. Not gonna happen, no way, no how.
There’s a bit of selective bias here, possibly a bit of hasty generalisation too - the same sorts of arguments were probably also made about a whole bunch of other ideas (such as atomic farming) and were right.
Why wouldn’t those planes are run off of biofuel or hydrogen (as that seems to be where the industry’s heading)? The carbon footprint is going to be relatively small in that case.
Again, how far out are you willing to go? Push the airport out too far, and even high speed rail solutions will be impractical. You also wind up with the issue of having to deal with another municipality if you go out farther. Say, City A’s airport is too crowded, and needs to expand, but the closest relatively undeveloped property (since that’s always going to be your first choice) is in the jurisdiction of City B, which wants nothing to do with the airport? You’ve then either got to try and negotiate with the folks at City B and hope they’ll change their mind, or you’ve got to look at developed areas within your own city, and all the headaches that entails.
As for wanting to land in a tunnel, people have said the same thing about traveling faster than 20 MPH, flying in any kind of plane, or going to the Moon. Time and circumstances change people’s perspectives. Frankly, I’m still leary of the thought of self-driving cars, but we’ll have them soon enough, and plenty of people will eagerly buy them.
Not that I really think we will be flying airplanes into tunnels in the foreseeable future, but if it ever comes to happen, it will probably start with military and/or cargo planes. After that becomes routine, then it will move to passenger planes (if they still exist by then). So it is not like tomorrow you need to convince grandma to get into one of those.
But nuclear power, and nuclear materials are used in growing crops. Sure, we’re not dumping plutonium (or whatever) on crops to make them grow faster, but even folks who knew anything about nuclear energy back then thought that was a stupid idea.
They will. What does that have to do with landing planes in dangerous tunnels?
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 is zero benefit to underground tunnels. There are manifold reasons against it. Just because you think it would be nifty doesn’t make it likely.
Let me say it again. There are no benefits to dangerous underground landing strips. 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.
Like the folks who knew anything about trains thinking it was a stupid idea to exceed 30mph?
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.