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Armchair air crash investigator

momav.me

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Re: Armchair air crash investigator

#51

Post by momavujisic »

mikeash wrote: post #43
tonylemesmer wrote: post #38

Earlier quoted context omitted.

I would hope the difference between a landing and a crash is a little more than 'feet' otherwise we'd have a lot more crashes. Maybe the difference between a BAD landing and a crash is only feet :)

A typical airliner approach is a 3 degree angle touching down at 1000ft past the end of the runway. That means that they pass over the threshold at about 150ft. Let's say there's another 1000ft past that before things get problematic (at SFO it's considerably less, I believe), that means that the airliner passes over the dangerous bit at about 300ft when operating normally, and 300ft lower would cause a crash. This i…

Just a note about approaches and landings – most, if not all airline ops usually say that you should be ~50ft when passing above the threshold.

Re: Armchair air crash investigator

#52

Post by mikeyouse »

proexploit wrote: post #25
Lusake wrote: post #4

Here is graphical comparison of safe landing and Asiana crash: https://pbs.twimg.com/media/BOhIDCWCUAApHFV.jpg:large . Also it appears that runway was modified: http://metabunk.org/sk/HL7742_777_Crash%2C_Korean_Asiana_Air...

Worth noting that with a modification like that, it looks like it actually gives extra space for landing, not less. So that piece probably isn't a factor at all.

Runway 28L at SFO is 10,800 feet long in its current configuration. The spec for the 777 is 5,800 feet of runway for landing[1]. There is obviously a fair amount of weight, wind dependency in determining the minimum required length, but the runway was almost 100% longer than was necessary.

[1] http://www.ana.co.jp/eng/aboutana/corporate/galleryclassi/19...

Re: Armchair air crash investigator

#53

Post by lisper »

aghull wrote: post #48
lisper wrote: post #45

Earlier quoted context omitted.

No, autoland is pretty good. But there are two factors that cause pilots to land manually most of the time: 1) pilots think they are better at handling last-minute unexpected contingencies like wind sheer or bird strikes (and they may well be right about that) and 2) pilots don't want to give the Powers that Be any additional data to suggest that they aren't actually needed to fly a plane at all. The fact of the matt…

I can't imagine anyone stepping onto an autonomous passenger aircraft for a long time, not until long after cars and smaller commercial aircraft are regularly driven using computers only. And even that seems like a stretch. I don't see how pilots use or non-use of some automated systems is going to influence popular opinion on that one way or another. But maybe there's a perception among pilots that it will.

The fact of the matter is that most commercial jetliners today are fully automated. It is only takeoff and landing that are still done by hand. No one ever hand-flies a jetliner during cruise except in dire emergencies. In fact, at high altitudes, where the plane is flying in the "coffin corner" of the flight envelope (http://en.wikipedia.org/wiki/Coffin_corner_(aviation)) hand flying can be extremely dangerous.

Re: Armchair air crash investigator

#54

Post by mikeash »

momavujisic wrote: post #51
mikeash wrote: post #43

Earlier quoted context omitted.

A typical airliner approach is a 3 degree angle touching down at 1000ft past the end of the runway. That means that they pass over the threshold at about 150ft. Let's say there's another 1000ft past that before things get problematic (at SFO it's considerably less, I believe), that means that the airliner passes over the dangerous bit at about 300ft when operating normally, and 300ft lower would cause a crash. This i…

Just a note about approaches and landings – most, if not all airline ops usually say that you should be ~50ft when passing above the threshold.

My simplistic analysis ignored the flare, thus why the real-world height would be lower. Thanks for pointing that out.

Re: Armchair air crash investigator

#55

Post by pbhjpbhj »

nostromo wrote: post #47

Curious as to why autopilot isn't being used to land planes yet. My understanding is that pilots can choose to use it to land, but only do so when visibility is very low. (ex: http://www.youtube.com/watch?v=DOFs-oa-bbc )

They mention that the ILS was off for repairs. Isn't that a major negative for doing autopilot landing (if indeed it's still allowed/possible without the external location based information).

Re: Armchair air crash investigator

#56

Post by RockyMcNuts »

RockyMcNuts wrote: post #36
vladd wrote: post #27

Earlier quoted context omitted.

There are some at http://flyingprofessors.net/what-happened-to-asiana-airlines...

like this link better than the OP which is fairly uninformed speculation ...

some video of the crash - kind of looks like it was skimming the waves in ground effect trying to go around

http://www.cnn.com/video/?/video/us/2013/07/07/vo-plane-sf-p...

I stand by the parent having some useful data and analysis, and the OP being totally speculation, and in many respects uninformed.

- number 1, if you say 'loss of power', makes sense as a possible cause. if you say 'icing in the FOHE', it's like saying the murder was done with a yellow pistol. nothing points to that, no icing conditions (humidity/temperature), and of course not same engine as the previous plane crash attributed to that

- number 2, you can't be unaware of an ILS out of op, you wouldn't be cleared for the ILS approach, you wouldn't be using the ILS on visual approach, you would be cued there's no signal, you wouldn't hear the outer marker, etc. etc.

- number 3, auto-throttle, well again, if you say malfunction in power setting, OK could make sense, if you get as specific as 'confliction with autopilot/auto throttle' that's a purple pistol. Clearly not on cat3 autoland, you're basically saying pilot forgot to set throttle in the right configuration for visual approach and landing.

- number 4, pilot error/bad approach, can't argue with that. the story is what's interesting, eg undiagnosed walleye vision, ate the bad fish etc.

Re: Armchair air crash investigator

#57

Post by VLM »

lukecampbell wrote: post #15
kop316 wrote: post #13

"The final bit of information is interesting. It shows a positive rate of climb – 120 feet per minute to be exact, which for a jet airliner, is very slow. For reference, at takeoff the vertical speed is most often +1500 feet per minute. Another interesting bit of information is the aircraft’s airspeed; 85 kts – for a Boeing 777 that is (and I’m guessing here) probably way below stall speed." That is actually expected…

I've never flown a B777 or any heavy aircraft so I can't comment on their typical flares, but in a Cessna 172 the flare doesn't induce a positive rate of climb, it simply slows the vertical descent speed to something manageable for touch down, a positive vertical speed seems counterintuitive to me as a good flare. What I want to know is what his IAS (indicated air-speed) at the decision altitude. Again the only thing…

It gives a pretty good estimate of the error involved in the descent rate reporting. Probably accurate +/- 200 FPM or so.

The airspeed encoder is probably from the same system that displays the pilot instruments, indicated airspeed IAS. I thought it odd that the analysis of conditions didn't think 125 and 98 were ridiculously low airspeeds, but claimed that an approach around 130 knots was a "fast approach". However what little I know about the 777 from the flightsim and real pilot community is that a typical approach is around 150-something slowing to a bit above 130 at flare. I've read some claims from actual heavy pilots that under really light conditions a Vref below 120 is theoretically possible.

None of us know the weight and balance calcs so its impossible to determine if the pilots were doing the correct thing, although it is possible to determine they were flying a flight path implying they thought they were very light indeed. Now why? Who knows. Maybe because they were right, they were light. Maybe because they were low-ish on fuel. Maybe they didn't trust their IAS instrument. Maybe their IAS was actually broken and comparing their visual approach with instruments, well, its just a really strong headwind today. Maybe they made a math error. Somebody overcontrolled?

He could have found this info by violating the copyright of numerous google-able flight sim forums, and forums with real genuine 777 pilots talking about their experience with the 777. Instead he violates the copyright of a picture which we've all already seen, oh well.

Re: Armchair air crash investigator

#58

Post by snom380 »

nostromo wrote: post #47

Curious as to why autopilot isn't being used to land planes yet. My understanding is that pilots can choose to use it to land, but only do so when visibility is very low. (ex: http://www.youtube.com/watch?v=DOFs-oa-bbc )

It's being used when needed. When not needed, pilots use the opportunity to practice landings. It's important to not get over-dependent on automation.

Re: Armchair air crash investigator

#59

Post by cpncrunch »

It looks like this was an unstabilized approach right down to the ground. It would be interesting to see what the company SOP is. Any safe airline has a no-fault go-around policy for unstabilized approaches, and you'll actually get in trouble if you continue with an unstabilized approach and you don't go around. From what pilots are saying on the message boards it seems that a lot of Asian airlines have pretty much the opposite policy - you get in trouble if you go around for any reason, and they would prefer you to salvage an unstabilized approach to save money.

Re: Armchair air crash investigator

#60

Post by snom380 »

rdl wrote: post #29

NY Daily News is reporting that VASI was down as well ( http://www.nydailynews.com/news/national/expert-runway-guida... ) Which appears to be due to someone incorrectly reading a post-crash NOTAM which is about the aids being gone due to the crash, so there's no particular reason to think VASI was down before the crash. I really don't think I'd trust SF city government to run an airport, even under FAA regulations. L…

I bet those other services aren't subject to frequent inspections by the FAA.
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