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Thanks for the detailed response. > Automatic landing systems rely on ground support by way of microwave signals from transmitters installed near autoland-capa
by 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...
- deleted 9y ago[deleted]
- phdp 9y ago> 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.). What is your definition of manual intervention? Pilots get updated instructions from the tower - the GPS path of the flight within 10 m is not programmed from the beginning due to weather issues, turbulence, traffic at the terminal ends, etc. The pilots hands may not be on the yoke, but they certainly are sending changes to the flight computer throughout the flight. > 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? Autopilot landings require a Cat III approach. There are currently no GPS (also known as GBAS for Ground Based Augmentation System) Cat III approaches approved in the US. The autopilot when landing is not using GPS for final approach. The pilot has pre-programmed in the waypoints labeled in the approach plate for the specific runway approach they've been told to take, and then they will switch over to the ILS approach. The tone of many comments here (yours too) call out people who actually know how the system works and question them. The person you're trading comments with has said twice that GPS is not responsible for the autolanding portion of the flight. They even gave a summary of how instrument landing works - microwaves transmitted on specific frequencies in a specific pattern. You twice try to refute it. And then in your last paragraph you do exactly what he says the software engineers here do and you take offense to! > sensible software engineers seem to regard aviation as a problem trivially susceptible of perfect solution > 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". Landing a big aircraft is not the easiest thing in the world, if only because the fate of hundreds of people rest in your hands. If you have a system that is designed to cut out the human component, it has to be all or nothing. As we learned from Asiana 214, when pilots have no actual practice doing something even in the absolute best of conditions and still cause loss of aircraft and life, how are they expected to perform when everything is going against them at the exact moment autolanding fails? Everything about flight training is preparing for the worst case, and practicing your skills over and over and over. Complacency can kill people when the margin of error between life and death is razor thin.