[0xffff2]

In this specific incident, there was a system in place called Runway Entrance Lights [0] that does serve as an automated sanity check on controllers commands. The surveillance video that is circulating shows that the system was working and indicated that the runway was not safe to enter. It's not clear yet why the truck entered the runway anyway.

0: https://www.faa.gov/air_traffic/technology/rwsl

[jamincan]

I wonder if they thought that since they were responding to an emergency, and they were given clearance to cross by ATC, that that would override normal procedures. Kind of like how emergency vehicles cross a red light all the time when responding to an emergency.

[AnAnonymousDude]

If they thought that, it was in error. Training SPECIFICALLY calls this out. The lights ALWAYS overrule the controller. Period.

[rectang]

It would be interesting to know whether that rule was onerous enough in practice that they had little choice but to break it in order to do their jobs effectively. They were responding to an emergency, seconds count, and they believed they had clearance from the controller.

[deathanatos]

> The surveillance video that is circulating shows that the system was working and indicated that the runway was not safe to enter.

A citation, please? The only video that I know of is [1].

[2] is my best mock up of the only video I have. I'm am not an expert, but my best read of that is that the RWSL is maybe? green to the taxiway¹ traffic, so, to me, the actual status of the RWSL at the time of the incident is "unknown"; that seems like something I should wait for the NTSB report, or at least someone with expert knowledge on. But your claims doesn't jive with the evidence I have, so that's what makes me ask for a citation.

[1]: https://www.youtube.com/watch?v=jRl7Vr87ym8&t=29

[2]: https://imgur.com/a/RVL28AV

¹but I think there are a number of problems with my own interpretation: I could be wrong about which lights are which; I am using the near-side lights, not the lights on the side the truck is entering from, and assuming them to be symmetrical (though what little I can see of the far side does seem to align with the near side); some of the lights I think are RWSLs & not RGLs look downright yellow, but that could be a property of the low quality of the video; there's the rather large problem of the plane on the runway that must then be explained.

[0xffff2]

https://www.reddit.com/r/CatastrophicFailure/comments/1s1mgc...

Sorry for the late reply, and sorry for linking to reddit, but it was the first place I could find the right video. I saw this video linked at least a dozen times in the hours following the incident. I believe the clip you linked to is from the same video, but with the beginning cut off.

At approximately 1.5 seconds in my link, you can see one set of lights perpendicular to the runway turn off. I admit the the lighting/colors are not as crisp as I would like, but the lights that turn off are positionally consistent with the Runway Entrance Lights and the time at which they turn off (approximately 2 seconds before the plane enters the intersection) is also consistent with the operation of the Runway Entrance Lights system.

Furthermore, if the system was not operational it should have been NOTAMed as such, and I can find no such NOTAM so my default position is that the system was operational.

[MBCook]

Why cross a runway at all? Can they not use taxiways and aprons to get there?

[7952]

You sometimes have end around taxiways that are at one end of the runway and can be used when active. But that could be a massive diversion.

I know that Heathrow have multiple fire stations and rendezvous points for emergency services so that fire service can attend even when one runaway is closed to crossing. This could be needed to allow continued operations following a crash. It allows them to accept emergency landings more easily whilst maintaining emergency service to another active runway.

[function_seven]

The fire station was located on the opposite side of runway 4 from the United plane. To avoid crossing the runway would mean having to travel a few extra miles around the thresholds (I assume).

I guess they could have found a route that wouldn't conflict with landing aircraft, but I doubt that's a practical option most of the time.

[deathanatos]

Plotting a course on Google Maps, I think this would add ~1.4 mi if you go around to get to the other side from where they were.

[xenadu02]

The REILs are part of ARFF training. Pilot training on it is also clear. The system is automated. It plots the direction and speed of anything approaching the runway and predicts a conflict. If the REILs are red it is HIGHLY likely there is a conflict that is missed by human error and you should not proceed without confirming. Don't just confirm cleared to cross, explicitly tell the controller "XYZ tower we have red runway entrance lights. Please confirm runway XX is clear".

The system is smart enough that if you get red bars to cross for an airplane departing once it passes your position the red clears because it knows the airplane is already past you. It is not dumb - it was deliberately designed to minimize false positives so everyone would trust it otherwise they might ignore it when it really counts. (AFAIK it very accurate in fact so the firetrucks weren't crossing because they distrusted the red lights).

This is just like all aviation incidents and indeed most incidents of any kind: the holes in the swiss cheese lined up.

The emergency aircraft couldn't find a free gate, creating a massive distraction for ATC, airport, et al. This is probably the primary domino that started the sequence. Had a gate been free this incident would not have happened. One big hole lined up.

Normally the aircraft would visually see the truck or the truck would visually see the airplane. But it was dark and rainy. Another hole lined up.

Everyone involved was rushing because noise abatement requires the airport to close at a certain hour. Thus everyone wanted to take-off or land before that shutdown. Another hole.

Normally the controller wouldn't issue the clearance to cross or their supervisor monitoring behind them would notice the error and override. But the controller and/or supervisor were distracted by the emergency. Another hole lined up.

The controller realized the error and issued a stop command but the fire truck proceeded anyway; they may or may not have heard the transmission. Another hole lined up.

Then someone else decided to jump on frequency during this busy time (we don't know who just yet) which may have prevented the controller's stop and/or go-around commands from being heard (another hole lined up).

The ARFF crew did not obey the REILs, accepting the clearance. Perhaps they thought the red lights were due to aircraft on short final and they still had time to cross? Perhaps it was some other misunderstanding of how that system works. Another hole lines up.

And the Air Canada jet was not paying attention to the chaos on frequency. There's a reason runway crossings are typically done on tower frequency: so aircraft can hear what is going on. But it was late at night and their brains probably didn't process what was happening. Or they were too close to touching down to have the bandwidth. Another hole lined up.

[krisoft]

> the holes in the swiss cheese lined up.

I totally agree with you on that.

> The emergency aircraft couldn't find a free gate, creating a massive distraction for ATC, airport, et al.

Yes. And I want to add one more thing to this: the airplane with the "odour" issue was kinda ambivalent about the danger. They deemed it dangerous enough to declare an emergency, and request a gate then later ask for airstairs but not dangerous enough to pop the slides and just evacuate right there and then. I'm not saying this is wrong. Obviously they were evaluating the situation as new information was coming in. But it increased the workload of the ATC. They were trying to find a gate, and etc. If it was a clearer "mayday mayday mayday, aft cabin fire, we are evacuating" that might have been paradoxically less "work" for the ATC. Or at least more of a "practiced" scenario.

> Perhaps it was some other misunderstanding of how that system works.

Yeah. That's a big one. Total speculation but maybe they thought the airplane with the "odour" issue was keeping it red?