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For everyone commenting about different hardware failure modes and possible solutions. Take a look at the airbus « flight control laws » such as https://apstrai

by oakmad 5y ago

For everyone commenting about different hardware failure modes and possible solutions. Take a look at the airbus « flight control laws » such as https://apstraining.com/wp-content/uploads/FCS-Airbus-Quick-Reference.pdf https://apstraining.com/wp-content/uploads/FCS-Airbus-Quick-... it governs what happens to flight controls and what protections are available in different scenarios. In this case the system worked, it crashed and reverted to direct law providing manual braking control. Off topic but I found this very interesting « 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. »

cwizou 5y ago
> 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.
- leecb 5y ago
  > 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 https://en.wikipedia.org/wiki/Airfield_rubber_removal
  - salawat 5y ago
    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.
  - ThePadawan 5y ago
    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=!3m1!1e3 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.
    - waynesonfire 5y ago
      i'm not surprised, look how invasive the cleaning techniques are.
- oakmad 5y ago
  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.
  - colechristensen 5y ago
    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.
    - dmurray 5y ago
      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.
      - AnimalMuppet 5y ago
        > 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.
jcrawfordor 5y ago
Build-up of rubber from the tires of landing airplanes is a routine problem with runway maintenance. Typically the airport authority will use a friction-measurement device at regular intervals to determine when the surface friction of the runway has fallen below required parameters, and resurface. But rain makes things much worse and might have combined with rubber build-up to produce a particularly slick section. Flying light aircraft, I was taught to avoid landing right in the touchdown zone just to have better traction. I'm not sure if this is actually useful or just Old Pilot Superstition but it has some logic to it, and putting a Skyhawk down on a 14k foot runway you have a lot of room for eccentric opinions (similar to landing just a touch off centerline so the nosewheel isn't on the painted stripes, another one I've heard people mention as a "best bad practice").
- rteuionwiv 5y ago
  I don't think anything too bad could happen when landing light aircraft on slippery but long runway. I was doing some winter flying and was landing pa28 on slippery runway (compressed snow) and I didn't noticed any difference until i started pressing brakes which had virtually no effect on deceleration. On touchdown you have a lot of aerodynamic authority on your controls so runway friction doesn't really matter unless you have super strong crosswind that could blow you out the runway i guess.
- azalemeth 5y ago
  My dad was a commercial pilot, and taught me to fly at a young age. One of the bits of sage advice was something along the lines of "if your nosegear has two or more wheels, try to get it bang on the centre line, every time. Otherwise, miss a little tiny bit. The lights go THUMP-THUMP-THUMP and eventually drive you mad or, combined with a little gust of wind, cause you to hop once more". I think there's a lot of Old Pilot Superstition with more than a dollop of truth in it.
- kylegordon 5y ago
  If I recall rightly Concorde pilots often took control from autoland and landed it slightly off the center line. This was to avoid upsetting the passengers and to ensure the champagne didn't get shaken too much.

by oakmad 5y ago

cwizou 5y ago

> 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.

leecb 5y ago
> 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 https://en.wikipedia.org/wiki/Airfield_rubber_removal
- salawat 5y ago
  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.
- ThePadawan 5y ago
  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=!3m1!1e3 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.
  - waynesonfire 5y ago
    i'm not surprised, look how invasive the cleaning techniques are.
oakmad 5y ago
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.
- colechristensen 5y ago
  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.
  - dmurray 5y ago
    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.
    - AnimalMuppet 5y ago
      > 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.

jcrawfordor 5y ago

Build-up of rubber from the tires of landing airplanes is a routine problem with runway maintenance. Typically the airport authority will use a friction-measurement device at regular intervals to determine when the surface friction of the runway has fallen below required parameters, and resurface. But rain makes things much worse and might have combined with rubber build-up to produce a particularly slick section. Flying light aircraft, I was taught to avoid landing right in the touchdown zone just to have better traction. I'm not sure if this is actually useful or just Old Pilot Superstition but it has some logic to it, and putting a Skyhawk down on a 14k foot runway you have a lot of room for eccentric opinions (similar to landing just a touch off centerline so the nosewheel isn't on the painted stripes, another one I've heard people mention as a "best bad practice").

rteuionwiv 5y ago
I don't think anything too bad could happen when landing light aircraft on slippery but long runway. I was doing some winter flying and was landing pa28 on slippery runway (compressed snow) and I didn't noticed any difference until i started pressing brakes which had virtually no effect on deceleration. On touchdown you have a lot of aerodynamic authority on your controls so runway friction doesn't really matter unless you have super strong crosswind that could blow you out the runway i guess.
azalemeth 5y ago
My dad was a commercial pilot, and taught me to fly at a young age. One of the bits of sage advice was something along the lines of "if your nosegear has two or more wheels, try to get it bang on the centre line, every time. Otherwise, miss a little tiny bit. The lights go THUMP-THUMP-THUMP and eventually drive you mad or, combined with a little gust of wind, cause you to hop once more". I think there's a lot of Old Pilot Superstition with more than a dollop of truth in it.
kylegordon 5y ago
If I recall rightly Concorde pilots often took control from autoland and landed it slightly off the center line. This was to avoid upsetting the passengers and to ensure the champagne didn't get shaken too much.