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Comment by ec109685 | Hacker News Reader

Given flight radar exits, why isn’t it possible to identify these situations in real-time reliably and alert there is a possible problem?

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From the linked twitter thread:

> For starters visibility was down to 1/8th of a mile. So tower likely never saw how close this was. Second off apparently Austin does not have ground radar. Regardless of that though this is the second near catastrophic accident we’ve had in two weeks or so here in the US alone.

Im surprised that radars arent an expectation for airports with big jets

To be clear, he's referring to _ground_ radar which tracks positions of aircraft on the ground. They all have radar monitoring nearby airspace.

https://en.wikipedia.org/wiki/Tenerife_airport_disaster

We've learned the lesson once already that not having ground radar is a bad idea.

Once? There was also a recent Cloudberg article about a place radar would've been real handy to have. (Plane and ground thought they were S of Kathmandu when they were N, until they suddenly went silent, due to hitting a mountain.)

Edit: Bah, wrong comment on the chain.

That’s a different problem. Regular radar is setup to detect flying aircraft and is very useful to avoid flying into mountains, avoid mid air collisions, etc and it’s not what we’re talking about. That type of Radar has proven necessary on many occasions.

Spending a great deal of money to track aircraft on the ground however is only helpful when one of the aircraft is on the ground. It’s only partially useful when visibility is low, at which point air traffic control can be especially paranoid.

I think the million flights after that point suggests otherwise.

Technology isn’t the only option, proper procedures can also work.

This is like saying "I don't wear my seatbelt because I've never been in an accident". Safety systems isn't about one or the other, it's about having multiple systems and procedures in place to prevent a disaster. Proper procedures are good, and it's a first line of defense, but humans make mistakes and are imperfect in other ways (Such as not being able to see through fog). Proper procedure in the case of near 0 visibility would be to greatly increase separation between planes, something which wasn't done in this case, and something which would slow down traffic a lot more than passengers and companies like.

It’s more like saying school busses don’t need seatbelts because based on a great deal of evidence, they don’t significantly improve school bus safety.

In this case the accident was avoided because aircraft could see each other long before there was a meaningful risk. It wasn’t a mismanaged zero visibility situation but rather proper procedures working.

It would interest me to know what the reasons are for ground radar not being more widespread and how many accidents are preventable by ground radar yearly. My first guess is that incidents where ground radar would've prevented them are so rare that it isn't worth the expense or the additional complexity or additional point of failure, and it's more productive/effective to solve the issue at different points in the system instead.

Right, but what's different about the way FlightRadar tracks planes? The planes themselves know where they are and can't that be communicated?

Yes: https://en.m.wikipedia.org/wiki/Traffic_collision_avoidance_...

FR24 is a combination of ground-based radar (both primary and secondary surveillance) and ADS-B data.

TCAS (as I understand it) uses the transponder part of secondary surveillance radar, but with out the bearing/ranging info, as well as ADS-B (if equipped).

TCAS is interesting but it’s not really relevant here. It’s something that is applicable to the en-route portion of a flight, when both planes are supposed to be separated by substantial distances while in the sky.

TCAS is useless in the terminal environment, like while landing or taking off. If it wasn’t inhibited (which it is) it would be correctly screaming that there are about to be a dozen airplanes too close for comfort every single time it got near an airport.

It’s a system for avoiding mid-air collisions not stuff like this.

My understanding is that when an aircraft is < 1000 AGL the TCAS would be at Sensitivity Level 2 (SL2) and they would still get Traffic Advisories (but not a Resolution Advisory); and only once landed and the pilot turns off TCAS would they no longer get messages?

These systems exist (STCA/RIMCAS for the tower, TCAS for the pilots, but not around landing), and for all we know at this point they might have helped avoid a collision. The challenge is balancing giving useful alerts while not feeding the pilots noise at the point that you want them to be absolutely dialed in.

Nothing currently comes close to human intuition for reliably detecting these sorts of collisions. Fundamentally when a plane is on final at an airport that's even remotely busy it's always on a collision course with planes on the runway taking off or landing.

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