[sonofhans]

I don't think the other answers are getting at the meat of it. Consider that those red lights functioning is the only thing keeping hundreds or thousands of people from getting killed. What sorts of safety and durability requirements would you impose on them? What sorts of maintenance and training requirements?

If nothing else they need to hold up in every weather and temperature big airports exist (-80ºF to +150ºF) and get run over by airplanes all day. Already that's a non-trivial problem.

[curun1r]

The other major concern is running reliable power to the lights. That isn’t something that can happen above ground when crossing runways, so there’s going to be at least some digging up the runway and repaving. Repaving runways isn’t cheap. It has to be done in an expedited manner since airports need all runways available during peak hours, so there’s usually a six-ish hour overnight window for work to get done and the runway left usable for the next day. This isn’t like normal roadwork where temporary metal plates can cover over unfinished work, so work must be done and the asphalt set during that window. This can mean large work crews doing highly-choreographed work that they’ve prepared (and even practiced) long in advance.

The costs add up quickly.

[defrost]

> so there’s going to be at least some digging up the runway and repaving.

The US doesn't have horizontal directional drilling rigs that go under a runway and pull cable?

[dredmorbius]

Oil and gas rigs typically don't have to worry about intersecting other infrastructure.

Even then, things occasionally go awry.

<https://en.wikipedia.org/wiki/Lake_Peigneur#Drilling_disaste...>

For an airport, the precision required both to not hit extant underground infrastructure and to know precisely where your newly deployed infrastructure is (for the next guy/gal to worry about) is probably a salient concern.

I'm not sure that horizontal drilling offers that degree of precision and assurance as opposed to rip-and-dig methods.

[defrost]

If you're not sure then you might like to forget about oil and gas drilling and look to suburban optic fibre cable laying in which a cable can be accurately laid following a curving S path about the countours of a curving road avoiding other known pipes over distances of 500+ m.

[dredmorbius]

Thanks.

Any references / sources on that?

[chha]

Sure they do. But then you have a tunnel under the runway that will flood and potentially freeze. Crumbling concrete and nonflat surfaces is not something you want on a runway or taxiway.

[defrost]

Then you have an electrical cable in a conduit.

As opposed to the alternative described, where you close down the runway, dig out a full trench, lay a cable in a conduit, and attempt to compact every thing back to how it used to be?

You think that's a better alternative than just drill core'ing the conduit through?

Interesting.

[julian_sark]

Why can't they have two huge, red, flashing lights at either side of the crossway, thus avoiding the costs to dig up runway asphalt altogether? Better than what they seemingly have now ...

[curun1r]

There may be designs that cut out some/most of the cost, but I made the comment because I watched a YouTube documentary on an airport that was making modifications and they had to dig up a bunch of the runways. They made a big deal out of the work, including working with a special contractor who had a practice area where they tried all the work they'd have to do ahead of time and timed themselves to be sure they could get the runway back in operating condition by the time it was needed. The amount of work they went through for something fairly minor was pretty memorable. I took from it that airports have a lot of logistical concerns that are pretty unique and the "that seems simple" take that I'd previously had about the tarmac portion of an airport being just a bunch of asphalt with some signs and lights on it was totally ignorant of all the complexity.

[akira2501]

> flashing lights at either side of the crossway

787 wingspan is 200ft (60m). Planes don't turn on a dime either, but the larger ones do have steering linked to the rear wheels, so their turn radius can be surprising.

The non invasive solution would be to require some kind of ground control computer link that can directly draw their controlled path for them on their displays and give them a nice loud master caution or warning if they're about to break their assignment.

Then we can start thinking about ground autopilot systems.

[a9h74j]

> and give them a nice loud master caution or warning if they're about to break their assignment.

Back in the days of the Exxon Valdez tanker incident, I wondered if the technology did not exist to positively track such major asset positions/directions, and dispatch an alarm from one or more authorities at a distance.

In terms of powering lights/signals, perhaps solar, batteries and a generator for each patch, and if there is no flashing of light visible (indicating power-loss or stuck-at failure), tower clearance must be given?

[thaumasiotes]

> 787 wingspan is 200ft

The lights don't need to be tall enough that the wings would be able to hit them.

[sokoloff]

These lights would not be the only thing keeping hundreds from being killed. ATC clearances over the radio are the primary thing; this is a secondary system.

[BoorishBears]

That's an example of why they're expensive: they need to be engineered as if one day they might be.

And no one chooses when or where that is

[tempestn]

That doesn't seem logical if the alternative is not having the lights at all.

[CoastalCoder]

> That doesn't seem logical if the alternative is not having the lights at all.

If the norm becomes (radio clearance and no red lights), I suspect pilots will become conditioned to equate no-red-lights with landing clearance. Not 100%, but maybe at least 1% of the time. So if that happens and the red lights stopped working, you have a problem that wouldn't have existed if the red lights were never introduced.

Perhaps a more resilient system would use green lights to indicate landing clearance. Then if the lights failed, the default would be radioing ATC for guidance?

(I have no qualifications on this topic. I'm just guessing based on a bunch of Mentour videos I've watched.)

[sokoloff]

These will always only be at a minority of airports and probably always be at a minority of airports with airline service.

[jonahx]

Exactly. The lights create a kind of moral hazard: https://en.wikipedia.org/wiki/Moral_hazard

[Cpoll]

I think https://en.wikipedia.org/wiki/Risk_compensation might be a better fit.

[paledot]

But my understanding is that the plane was taxiing. At this point, the problem isn't just the lack of red lights: the pilot took a wrong turn. There are reasons other than the possibility of crossing an active runway why you follow directions, among them that you want to end up at your destination.

[tempestn]

That's a good point; if pilots come to expect the lights, I can see how it could be dangerous for them to fail, even if they're not supposed to be the primary mechanism.

[nkozyra]

An unreliable system is often worse than a non-existent one.