Coincidentally-identical waypoint names foxed UK air traffic control system

I believe when OP said 'treated this as a late validation error', they were acknowledging the inevitability of bugs and root cause-ing "why did a single failure to validate cause the entire system to fall over rather than reject the single flight plan in question." The words 'treated this as' are load bearing here.

> such identical designators should be geographically widely spaced

Yes, though I wouldn't normally regard "4,000nm" (mentioned in the article) as widely spaced in geographical terms. Unless they meant nautical miles (which should be abbreviated as M, NM, Nm or nmi according to en.wiktionary.org) rather than nanometres.

OK, perhaps that comment wasn't really worth making ...

On the other hand, perhaps next year we'll read about some other system (aviation or silicon design) collapsing because the software mixed up nanometres and nautical miles.

Imagine the dread if they find out who wrote the code.

Also to be honest, shouldn't this have been better unit tested? Considering aviation is a ~ £60 billion industry for the UK.

A defensively programmed safety critical system should reject (loudly) the offending flight plan (and its permission to fly in the airspace) rather than shut itself off and leave all the planes flying (currently and in the foreseable future) to figure things out for themselves.

> But the flight plan wasn't erroneous - it was perfectly valid.

Well. Then the real issue is that a single flight plan, erroneous or not, should not stop the full system. It should flag that flight plan for problem resolution and keep on working with the rest of the flight plans.

Would result in a slightly inconvenienced flight dispatcher, or worst case an inconvenienced flight, instead of a nationwide shutdown.

> If someone had put an extra waypoint in between the two, nothing would have broken (AIUI).

I don't see it said anywhere that the two same-named waypoints were consecutive, with no other points between them. Just that they were "approximately 4000 nautical miles apart". Or that being consecutive duplicates rather than just duplicates was the cause.

Since they don't name the waypoints, it is very vague.

To a human. To a computer, it was degenerate.

Well they can reject the bad flight plan and the plane will not be allowed to follow it.

> Why should it be possible to continue when a single flight plan is wrong?

To make the system resilient.

Note: When the error happened the flight was not in the air yet. The system in question received the flight plan 4 hours before departure time. If the system would have flagged the flight plan as bad they could have called them and told them that they can't fly. If not that they could have refused them when they were entering the airspace. Can happen any time for any reason.

> Naïvely it sounds like having even a single plane in an unknown position would make safe automated control impossible.

Flight plans are not for knowing the position of the plane.

> Is that wrong?

Slightly.

> make safe automated control impossible

First, you don't understand the purpose of a flight plan. The purpose of the flightplan safety.

You, the captain, are saying "My intention going from A to Z via K,J and X". You then "activate" your flightplan over the radio upon departure.

The purpose of the flightplan is so people on the ground broadly have an idea of where you are and when you'll arrive. The former is to assist with co-ordination between control zones. The latter is so that if the destination airport doesn't see you X hours after your ETA, then they can start searching along the filed route until they find the debris of your crashed aircraft.

Second, you need to take "automation" out of your thinking. Flight crew don't just punch the plan into the nav and sit there twiddling their thumbs.

Shit happens and the crew might need to deviate from the plan. It happens all day every day. There might be some horrible weather ahead that you want to route around. There might be something happening in the airspace around you that ground might want to route you around.

Therefore flight plan merely describes your INTENTION.

Airspace Adaptation, or the catalog of different items in the old ATC system, is nightmarishly complex. It allows for insane FPs that are just not suited for straight forward computation. Canada and Mexico also share fix names with US. From a math and physics perspective, the language of flight plans is degenerate and, I think, doesn't even hold group structure. It's the reason that humans are still required even though MIT's JEDI did a bang up job of conflict resolution, or keeping planes from giving each other hugs. on the nose. At 300 miles per hour.