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UK air traffic control meltdown

jameshaydon.github.io

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Re: UK air traffic control meltdown

#421

Post by Rochus »

spuz wrote: post #403
Rochus wrote: post #247

Earlier quoted context omitted.

Since it's not Reddit but HN, it's all the stranger to dismiss a perfectly legitimate question. But times and mores seem to change much faster than I realize.

It's because your question was poorly phrased - it sounds like you are trying to dismiss the value of the submission for no apparent reason. If you genuinely want to know the answer to a question, don't start with your conclusion and append "isn't it?" to turn it into a question. Just say something like "I don't have time to read the article. Does the author provide any industry expertise to the incident beyond what…

It's not poorly phrased. It's my conclusion after spending ten minutes with the text and I was interested whether others came to the same conclusion, which apparently is the case. It also turned out that the author is not even a specialist and has no affiliation with an involved organization. But apparently people prefer to read and discuss arbitrary opinions.

Re: UK air traffic control meltdown

#422

Post by pmarreck »

robocat wrote: post #367
pmarreck wrote: post #364

Earlier quoted context omitted.

There are a number of word lists whose words were picked due to their beneficial properties given the use-case of possibly needing to be understood verbally over unclear connections. The NATO phonetic alphabet, and PGP word lists come to mind: https://en.wikipedia.org/wiki/PGP_word_list I'm particularly a fan of the PGP word list (it would definitely require more than 3 words for this purpose, though) because it has…

> I'm particularly a fan of the PGP word list As a New Zealander, the PGP list is unfriendly because there are plenty of words that are hard to spell, or are too US centric. dogsled (contains silent d, and sleigh might be a British spelling) Galveston (I've never heard of the place) Geiger (easy to type i before e - unobvious) Wichita (I would have guessed the spelling began with which or witch) And why did the desig…

Great ideas all!

It should be discussed like this! It's clear that the w3w people didn't even do the bare minimum here!

The thing is, once you agree that some words are subpar or need translations, you can do a 1-to-1 mapping.

The problem with What3Words is that supporting the original word set will always be a pain even if they release a v2 word set with a 1-to-1 mapping (I believe they've already released versions for other languages?)

re: Geiger- parsing it could trivially accept misspellings of words

Re: UK air traffic control meltdown

#423

Post by bdavbdav »

xp84 wrote: post #344
nightpool wrote: post #331

Earlier quoted context omitted.

not stronger isolation between different flight plans? it seems "obvious" to me that if one flight plan is causing a bug in the handling logic, the system should be able to recover by continuing with the next flight plan and flagging the error to operators to impact that flight only

I'm no aviation expert, but perhaps with waypoints: A B C D E / F G H I J If flight plan #1 is known to be going from F-B at flight level 130, and you have a (supposedly) bogus flight plan #2, they can't quite be sure if it might be going from A-G at flight level 130 at the same time and thus causing a really bad day for both aircraft. I'd worry that dropping plan #2 into a queue for manual intervention, especially i…

I'm not sure they're even used for that purpose - that side of thing is done "live" as I understand it - the plans are so that ATC has the details on hand for each flight and it doesn't all need to be communicated by radio as they pass through.

Re: UK air traffic control meltdown

#424

Post by bdavbdav »

WalterBright wrote: post #379
borissk wrote: post #336

Earlier quoted context omitted.

Different teams often make the same mistake. The system you describe is not perfect, but makes sense.

I neglected to mention there was a third party that reviewed the algorithms to verify they weren't the same. Nothing is perfect, though, and the pilot is the backup for failure of that system. I.e. turn off the stab trim system.

Is this still the case for simple algorithms?

Re: UK air traffic control meltdown

#425

Post by gabereiser »

retrocryptid wrote: post #297
DyslexicAtheist wrote: post #278

Earlier quoted context omitted.

> Pilots occasionally have to fat finger them into ruggedized I/O devices you're saying what-3-words (W3W) is unsuitable for safety critical applications ? /s

Something like what3words might be useful, but what3words itself doesn't have enough "auditory distance" between words. (i.e. - there are some/many words used by what3words that sound similar enough to be indistinguishable over an audio channel with noise.) Something like FixPhrase seems better for use over radio.

what3words is not useful at all. 1) FAA (and thus the world) have a hard character limit of 8, this is to support old mainframes running (Delta, I'm looking at you) old unix dispatch software. 2) The cockpit computers have limited characters on screen. A FMC can display 28 characters x 16 rows at best. Most are 8 rows. Military aircraft have some that are 2 rows. The FMC or Flight Management Computer is really just an old embedded chip. 3) The entire airline, flight, tourism, booking, and ticketing systems of the world would need to change. Including all legacy systems, all paper charts, all maps, all BMS's, all AirBoss's, all ATC software, all radio beacons. There is no chance that any of this will change simply because someone came up with a way to associate words with landmarks you can't see from the air.

Re: UK air traffic control meltdown

#426

Post by jefftk »

jwr wrote: post #400
wcarss wrote: post #341

Earlier quoted context omitted.

This reminds me of a backwoods hike I took with a friend some years back. We each brought a compass, "for redundancy", but it wasn't until we were well underway that we noticed our respective compasses frequently disagreed. We often wished we had a third to break the tie!

My grandfather was working with Stanisław Skarżyński, who was preparing for his first crossing of the Atlantic in a lightweight airplane (RWD-5bis, 450kg empty weight) in 1933. They initially mounted two compasses in the cockpit, but Skarżyński taped one of them over so that it wasn't visible, saying wisely that if one fails, he will have no idea which one is correct.

> if one fails, he will have no idea which one is correct

Depends how it fails! For example, say, when you change direction one turns and the other doesn't.

Re: UK air traffic control meltdown

#427

Post by tjohns »

gorgoiler wrote: post #357
WalterBright wrote: post #329

Earlier quoted context omitted.

I also understand that it is impractical to implement the ATC system software twice using different algorithms. The software at least checked for an illogical state and exited, which was the right thing to do. A fix I would consider is to have the inputs more thoroughly checked for correctness before passing them on to the ATC system.

I wonder where most of the complexity lies in ATC. Naively you’d think there would be some mega computer needed to solve the puzzle but the UK only sees 6k flights a day and the scale of the problem, like most things in the physical world, is well bounded. That’s about the same number of buses in London, or a tenth of the number of Uber drivers in NYC. It would be interesting to actually see the code.

Much of the complexity is in interop. Passing data between ATC control positions, between different facilities, and between different countries. Then every airline has a bidirectional data feed, plus all the independent GA flights (either via flight service or via third-party apps). Plus additional systems for weather, traffic management, radar, etc. Plus everything happening on the defense side.

All using communication links and protocols that have evolved organically since the 1950s, need global consensus (with hundreds of different countries' implementations), and which need to never fail.

Re: UK air traffic control meltdown

#428

Post by dundarious »

jameshh wrote: post #365
t0mas88 wrote: post #302

Earlier quoted context omitted.

They use the ADEXP to determine which part of the route is in the UK. Because the auto generated points are ATC area handover points. So this data is the best way so see which part of the route is within the UK airspace. Then it needs to find the ICAO part that corresponds, because the controller needs to use the ICAO plan that the pilot has. If the controller sees other (auto generated) waypoints that the pilots don…

Thanks for this explanation. So, is the ICAO plan in some sense the "single source of truth", being the international standard and all?

Yes, thanks, t0mas88. I have some more questions but I can feel myself drifting into the weeds a bit, and your comment was extremely helpful as-is.

Re: UK air traffic control meltdown

#429

Post by Pxtl »

tjohns wrote: post #351
Pxtl wrote: post #339

Earlier quoted context omitted.

If only there was a globally unique set of short two-letter names for every country that could be used as prefixes to enforce uniqueness while still allowing every country to manage their own internal waypoint list. If only.

I'm sure they thought about this at some point. Airports already have a country-code prefix. (For example, airports in the Continental US always start with K.) For whatever reason, by convention navaids never use a country prefix. Even when it would make sense - the code for San Francisco International Airport is "KSFO", but the identifier for the colocated VOR-DME is just "SFO". (Sometimes this does make a big diffe…

Yes, but country-prefixes are something you could migrate gradually in a backwards-compatible way.

"Waypoint Charlie Alpha Dash ALKOG, over."

"This is an old machine, so just ALKOG then, over."

Re: UK air traffic control meltdown

#430

Post by cratermoon »

touisteur wrote: post #370
cratermoon wrote: post #235

Earlier quoted context omitted.

There's a difference between parsing and validating . https://lexi-lambda.github.io/blog/2019/11/05/parse-don-t-va... You're right about all the buggy stuff out there, and that nobody wants to pay to make it better, though.

From a safety-critical standpoint, I've always found this article interesting but strange. You want both, before taking into account any data from anything outside of the system. Do both. As soon as possible. Don't propagate data you haven't validated in any way your spec says so. If you have more stringent specs than any standard you're using, be explicit about it, reject the data with a clear failure report. Check…

> It's not that hard, compared to many other proof and safety/security endeavours.

Yes, but the code has to understand and model the input into a program representation: the AST. That's the essence of the "parse, don't validate" paradigm. Instead of looking at each piece of a blob of data in isolation to determine if it's a valid value, turn the input into a type-rich representation in the problem domain.

In the case of the FPRSA-R system in question, it does none of that. It's simply a gateway to translate data in format A to data in format B, like an ETL system. It's not looking at the input as a flight plan with waypoints, segments and routes.

Why the programmers chose to do the equivalent of bluescreening on one failed input, I can't say. As others have pointed out, the situation it gave up on isn't so rare: 1 in 15 million will happen. Of course switching to an identical backup system is a bad choice, too. In safety-critical work, there needs to be a different backup, much like the Backup Flight System in the space shuttle or the Abort Guidance System on the Apollo Lunar Module: a completely different set of avionics, programmed independently.

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