Hacker News Reader

Comment by cwizou | Hacker News Reader

> The deceleration performance of the occurrence flight between 6,600 feet and 7,300 feet from the threshold of runway 10 deteriorated. It may be due to paint marking and rubber deposit on the touchdown zone of runway 28

Just to clarify for others, this is the same runway but taken in two different directions (west to east and east to west, multiply the number by 10 and you get [rounded] angle in degree, so 100ish vs 280ish). It's 8500 ft. long and it looks like there was a loss of performance around the "touchdown" point of going the other way on that runway, where you had accumulated rubber from those landings (which is pretty normal and monitored, as pointed by leecb below), if that makes any sense.

View on HN

> accumulated rubber from those landings

Rubber accumulation on runways is a normal and expected situation. Part of runway maintenance at airports serving larger aircraft includes regular removal of the rubber using high pressure water or chemicals.

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

Not going to lie, I never thought this was a thing that'd need doing, but on further reflection it seems so obvious I'm kinda mad it never occurred to me in retrospect.

I'm still always surprised just how much rubber is allowed to accumulate.

Here's a snapshot of one of the Zurich runways: https://www.google.com/maps/@47.4792249,8.5411849,660m/data=...

Scroll a little NW or SE to see what the actual color of the runway is underneath all the rubber.

i'm not surprised, look how invasive the cleaning techniques are.

Its unfortunate they don’t calculate how big a difference it made. They’d calculated a 170ft margin and stopped with 30ft margin and I’m curious what their braking delta was for that 700ft of deterioration.

« With three FCPCs inoperative, actual remaining runway distance (30 feet margin) of the occurrence flight was shorter than the calculated value (172 feet margin), possibly due to tailwinds, runway conditions, and manual braking as these factors might increase the braking distance. »

I get sucked into how all the little things that are not right make such a big difference in these kind of scenarios.

Complex systems and aerospace particularly are dominated by little things. Failure or near misses are never single cause, those are all designed for. When fails to happen it is almost always a conspiracy of serval things out put together any one of which would have mostly prevented the incident.

There is a lot that practices involving life critical complex systems can teach other fields.

Agreed, and let's not lose sight of the fact that...this was a successful landing. Everyone walked away from it and the passengers likely never knew anything went wrong.

Four hopefully independent things went wrong here: three computer failures plus less-than-documented braking performance. Additionally, there were at least two aggravating circumstances: wet conditions and a tailwind landing. Part of the investigation is to find out if there was a fourth or fifth system failure (poor pilot reaction time? Rubber level on the runway unacceptable? Either is plausible, but far from indicated by the report so far).

One extra thing going wrong here, in the wrong direction (anything that impaired braking or pilot reaction time) would likely have led to loss of life. Investigating near misses like this, and not only being exercised once five things go wrong and a hundred people die, is a sign of a healthy safety culture.

> the passengers likely never knew anything went wrong.

If the deceleration varied as much as the report said, then the passengers probably could tell. That was very different from a normal landing. If that wasn't enough, being towed to the terminal might have given them another clue.

> One extra thing going wrong here, in the wrong direction (anything that impaired braking or pilot reaction time) would likely have led to loss of life.

Well, it would have lead to the plane running off the end of the runway. What's past the end of that particular runway? A cliff? A river? Or just another 100 meters of grass leading up to a perimeter fence, then more flat ground for some distance beyond it? If it doesn't overrun the runway too far (say, 100 or 200 meters), no, that doesn't seem likely to lead to loss of life - not unless there's some specific hazard there.

According to the first comment on TFA, it's in a built up area. I checked Google maps [0] and it's pretty bad: 50m of tarmac (no EMAS I think), 50m of grass, then a minor road with commercial buildings.

Regardless, that's one to be considered another aggravating circumstance, not an additional failure. When deciding whether this was a close call, you can treat it as if every runway is wet and in a permanent tailwind and immediately followed by a wooden building full of schoolchildren.

[0] https://maps.app.goo.gl/u4eFmqDAysMVbbWC8

Oh, absolutely. You treat it as if there is no margin.

And you don't put wooden buildings full of schoolchildren immediately past the end of runways.

Unless I am mistaken, runway 10 is west to east so it would have gone through the parking lot and then into the river. That also the direction I remember most planes landing there.

Overshooting the runway isn't that bad, it's expected in emergency scenarios. In those cases, minor injuries and extensive damage to the aircraft are accepted in favor of something worse. Usually you find rubble pits and soft earth behind a runway for the nose gear to dig into, a 10-20ft drop on the nosegear will hurt but the aircraft is now breaking with it's entire front, not just a rubber wheel. The Mayday TV show had a few incidents where the aircraft overshot and that happened.

I read this in an old 1950s era Readers Digest (Harper Subscribers only). Interesting (fictional) article about a jet that was doomed before takeoff by an accumulation of a number of small things each of which would not individually have caused an incident but taken together were fatal. https://harpers.org/archive/1957/09/the-jet-that-crashed-bef...

Edit: Accessible version of the article here. https://books.google.co.in/books?id=2gk-2rP34LIC&pg=RA2-PA14...

Reply on news.ycombinator.com