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Okay so let me get this straight: you're telling me that passenger airplanes currently fly by dead reckoning or stellar navigation or ground-based triangulation

Okay so let me get this straight: you're telling me that passenger airplanes currently fly by dead reckoning or stellar navigation or ground-based triangulation or something else? When a pilot doesn't know where he is, he doesn't have any kind of certified GPS-based system handy to tell him? And moreover, even beyond GPS: how the hell can a plane's navigation system be capable of (and certified for!) landing the monster under autopilot, and yet not be able to tell the pilot its own location within the accuracy of a few feet reliably? I literally do not understand how what you're saying makes any sense.

throwanem 9y ago
Automatic landing systems rely on ground support by way of microwave signals from transmitters installed near autoland-capable runways. There's no general position information, and the airborne part of the system can't operate independently of the part on the ground. Civilian GPS signals are limited in terms of position accuracy, too. I believe the CEP is ten meters. That's not bad, but it's not good enough to land an aircraft. Altitude information from GPS is (IIRC) either nonexistent or severely limited, too. About any aircraft with a glass cockpit is going to support a moving map display, and those do see use - but, as a couple of professional pilots in this thread have noted, during final approach the main concern with regard to aircraft position is relative to the glide slope and the runway, and a moving map has nothing to do with any of that. On a more general note, it is remarkable to me that so many otherwise apparently sensible software engineers seem to regard aviation as a problem trivially susceptible of perfect solution - every time we here on HN discuss any sort of mishap even peripherally involving any aircraft, the same suggestions invariably arise around automation, various schemes of runway lighting, cockpit lighting, instrument augmentation or replacement, pilot augmentation or replacement... One would tend to imagine that the history of our attempts to perfect our own craft - including those attempts which we who build and maintain software make anew every day - would give us cause for humility on the subject of fields other than our own, about which in the main we know next to nothing. Imagine five hundred airline pilots confecting an ad-hoc, long-distance postmortem of the recent us-east-1 incident! You'll have to imagine it, because it did not happen - and it is rare at best in my experience for pilots, because they are skilled in one highly complex and technical field, to imagine they can speak authoritatively in the context of another. Perhaps we might profit by their example.
- wfunction 9y ago
  Thanks for the detailed response. > Automatic landing systems rely on ground support by way of microwave signals from transmitters installed near autoland-capable runways. There's no general position information, and the airborne part of the system can't operate independently of the part on the ground. Yes, I understand the landing portion has other kinds of support. However, I don't understand how it can not have the positioning information we need, because {see next response below}. > Civilian GPS signals are limited in terms of position accuracy, too. I believe the CEP is ten meters. That's not bad, but it's not good enough to land an aircraft. Altitude information from GPS is (IIRC) either nonexistent or severely limited, too. About any aircraft with a glass cockpit is going to support a moving map display, and those do see use - but, as a couple of professional pilots in this thread have noted, during final approach the main concern with regard to aircraft position is relative to the glide slope and the runway, and a moving map has nothing to do with any of that. This seems to contradict with what I read [1]. See this quote, for example: Generally, the pilot will handle takeoff and then initiate the autopilot to take over for most of the flight. In some newer aircraft models, autopilot systems will even land the plane. OK, so I don't have much of an expectation for older plane models, but my interpretation of the above is that in newer models, autopilot need not disengage before landing and require manual intervention in order to align the plane with the correct track (barring bad weather or other unusual situations like bird collisions, etc.). This is supported by the fact that they later explicitly mention that autopilot occasionally disengages. So it seems clear in normal situations autopilot has plenty of positioning available to it, enough to find the runway and locate the plane on a display of some sort. That goes pretty clearly against what you said. Am I missing something? > On a more general note, it is remarkable to me that so many otherwise apparently sensible software engineers seem to regard aviation as a problem trivially susceptible of perfect solution I hope this isn't referring to me, because I've been trying pretty hard not to give that impression (which I don't have). I never suggested anything about aviation perfection in general. I'm specifically talking about this particular kind of problem, because it seems to me that with current technology, pilot errors of this kind should be completely avoidable using current technology and, basically, non-problems in the first place. (Again: note that I said these types of pilot errors should be avoidable. I didn't say all faulty landings on the wrong tracks should be unavoidable.) In other words, nowhere did I suggest that I think airplanes can fly or land themselves perfectly in unfavorable conditions. But this was quite a favorable condition for an automated system. And, as a computer scientist, what seems ridiculous to me is the idea that "Oh, but this system you just described won't work if there is a hurricane and there are turkeys getting rammed through our engines while the pilots are asleep and ATC happens to be on strike in the middle of a nuclear holocaust, so let's "be conservative" and never approve it because it's clearly going to make things worse on average". [1] http://www.cnbc.com/2015/03/26/autopilot-what-the-system-can-and-cant-do.html http://www.cnbc.com/2015/03/26/autopilot-what-the-system-can...
Piskvorrr 9y ago
Seriously? From here, it looks as if you're doing your best in refusing to understand. Here's a hint: context. If you're en route, even an approximate position within hundreds of feet is great for navigation; please stow your straw men back where you found them. In this case, the issue is with landing, where you need a precise position; "probably tens of feet, when it works" is exactly the sort of accuracy that's not good enough. As for "know where it is and land" - that's already there, is called Precision ILS, and uses no elements of GPS whatsoever.
- wfunction 9y ago
  The issue is you're treating this as though (1) cruising can be done on autopilot via GPS because it doesn't need much accuracy, (2) landing can also be done on autopilot because we have more accurate systems, but (3) the transition between the two requires manual intervention because the plane can't reliably locate itself accurately enough to get in the right position for landing systems to take over. But that simply doesn't seem to be the case (in normal weather, which we had here). See my reply to a sibling comment here for a link. It seems that in normal conditions planes are capable of doing it all in one go, which means they are capable of accurately and reliably locating themselves. Nobody is expecting these to work in extreme conditions like bad weather or bird collisions, but in those conditions autopilot can and does already get disengaged (whether automatically or manually), and this could be done the same way. It's not like we forbid autopilot entirely because it isn't 100% perfect, so why not apply the same standards here?
  - Piskvorrr 9y ago
    Nope. (3) The transition between the two requires manual intervention, as those are very different flight modes, using different systems and there's no automagic way to switch between them; the quote from the linked article is an oversimplification akin to "computers can do almost anything - therefore what do we need programmers anyway?"

throwanem 9y ago

Automatic landing systems rely on ground support by way of microwave signals from transmitters installed near autoland-capable runways. There's no general position information, and the airborne part of the system can't operate independently of the part on the ground. Civilian GPS signals are limited in terms of position accuracy, too. I believe the CEP is ten meters. That's not bad, but it's not good enough to land an aircraft. Altitude information from GPS is (IIRC) either nonexistent or severely limited, too. About any aircraft with a glass cockpit is going to support a moving map display, and those do see use - but, as a couple of professional pilots in this thread have noted, during final approach the main concern with regard to aircraft position is relative to the glide slope and the runway, and a moving map has nothing to do with any of that. On a more general note, it is remarkable to me that so many otherwise apparently sensible software engineers seem to regard aviation as a problem trivially susceptible of perfect solution - every time we here on HN discuss any sort of mishap even peripherally involving any aircraft, the same suggestions invariably arise around automation, various schemes of runway lighting, cockpit lighting, instrument augmentation or replacement, pilot augmentation or replacement... One would tend to imagine that the history of our attempts to perfect our own craft - including those attempts which we who build and maintain software make anew every day - would give us cause for humility on the subject of fields other than our own, about which in the main we know next to nothing. Imagine five hundred airline pilots confecting an ad-hoc, long-distance postmortem of the recent us-east-1 incident! You'll have to imagine it, because it did not happen - and it is rare at best in my experience for pilots, because they are skilled in one highly complex and technical field, to imagine they can speak authoritatively in the context of another. Perhaps we might profit by their example.

wfunction 9y ago
Thanks for the detailed response. > Automatic landing systems rely on ground support by way of microwave signals from transmitters installed near autoland-capable runways. There's no general position information, and the airborne part of the system can't operate independently of the part on the ground. Yes, I understand the landing portion has other kinds of support. However, I don't understand how it can not have the positioning information we need, because {see next response below}. > Civilian GPS signals are limited in terms of position accuracy, too. I believe the CEP is ten meters. That's not bad, but it's not good enough to land an aircraft. Altitude information from GPS is (IIRC) either nonexistent or severely limited, too. About any aircraft with a glass cockpit is going to support a moving map display, and those do see use - but, as a couple of professional pilots in this thread have noted, during final approach the main concern with regard to aircraft position is relative to the glide slope and the runway, and a moving map has nothing to do with any of that. This seems to contradict with what I read [1]. See this quote, for example: Generally, the pilot will handle takeoff and then initiate the autopilot to take over for most of the flight. In some newer aircraft models, autopilot systems will even land the plane. OK, so I don't have much of an expectation for older plane models, but my interpretation of the above is that in newer models, autopilot need not disengage before landing and require manual intervention in order to align the plane with the correct track (barring bad weather or other unusual situations like bird collisions, etc.). This is supported by the fact that they later explicitly mention that autopilot occasionally disengages. So it seems clear in normal situations autopilot has plenty of positioning available to it, enough to find the runway and locate the plane on a display of some sort. That goes pretty clearly against what you said. Am I missing something? > On a more general note, it is remarkable to me that so many otherwise apparently sensible software engineers seem to regard aviation as a problem trivially susceptible of perfect solution I hope this isn't referring to me, because I've been trying pretty hard not to give that impression (which I don't have). I never suggested anything about aviation perfection in general. I'm specifically talking about this particular kind of problem, because it seems to me that with current technology, pilot errors of this kind should be completely avoidable using current technology and, basically, non-problems in the first place. (Again: note that I said these types of pilot errors should be avoidable. I didn't say all faulty landings on the wrong tracks should be unavoidable.) In other words, nowhere did I suggest that I think airplanes can fly or land themselves perfectly in unfavorable conditions. But this was quite a favorable condition for an automated system. And, as a computer scientist, what seems ridiculous to me is the idea that "Oh, but this system you just described won't work if there is a hurricane and there are turkeys getting rammed through our engines while the pilots are asleep and ATC happens to be on strike in the middle of a nuclear holocaust, so let's "be conservative" and never approve it because it's clearly going to make things worse on average". [1] http://www.cnbc.com/2015/03/26/autopilot-what-the-system-can-and-cant-do.html http://www.cnbc.com/2015/03/26/autopilot-what-the-system-can...

Piskvorrr 9y ago

Seriously? From here, it looks as if you're doing your best in refusing to understand. Here's a hint: context. If you're en route, even an approximate position within hundreds of feet is great for navigation; please stow your straw men back where you found them. In this case, the issue is with landing, where you need a precise position; "probably tens of feet, when it works" is exactly the sort of accuracy that's not good enough. As for "know where it is and land" - that's already there, is called Precision ILS, and uses no elements of GPS whatsoever.

wfunction 9y ago
The issue is you're treating this as though (1) cruising can be done on autopilot via GPS because it doesn't need much accuracy, (2) landing can also be done on autopilot because we have more accurate systems, but (3) the transition between the two requires manual intervention because the plane can't reliably locate itself accurately enough to get in the right position for landing systems to take over. But that simply doesn't seem to be the case (in normal weather, which we had here). See my reply to a sibling comment here for a link. It seems that in normal conditions planes are capable of doing it all in one go, which means they are capable of accurately and reliably locating themselves. Nobody is expecting these to work in extreme conditions like bad weather or bird collisions, but in those conditions autopilot can and does already get disengaged (whether automatically or manually), and this could be done the same way. It's not like we forbid autopilot entirely because it isn't 100% perfect, so why not apply the same standards here?
- Piskvorrr 9y ago
  Nope. (3) The transition between the two requires manual intervention, as those are very different flight modes, using different systems and there's no automagic way to switch between them; the quote from the linked article is an oversimplification akin to "computers can do almost anything - therefore what do we need programmers anyway?"