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Armchair air crash investigator

momav.me

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Re: Armchair air crash investigator

#11

Post by gklitt »

pcl wrote: post #7
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...

Interesting. I wonder what the Asiana's descent profile looks like compared to the average and some outliers of other safe 777 landings at SFO. Did you generate that image? If not, what was the source?

I saw another image online, which compared the descent profiles of the past week of landings for the same flight. It showed that the July 6th landing was very close to the normal descent profile, and the July 5th landing was actually the outlier -- it had an unusually shallow glide slope.

Unfortunately I can't find the image right now, but perhaps someone else knows where it is and can provide it?

Re: Armchair air crash investigator

#13

Post by kop316 »

"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. It is called the flare just before touchdown:

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

Re: Armchair air crash investigator

#15

Post by lukecampbell »

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 I've flown are parachutes and some hours in a C172 and a C182.

Re: Armchair air crash investigator

#16

Post by stcredzero »

austenallred wrote: post #3
bdirgo wrote: post #2

I heard a reporter on TV reporting that the airplane was doing cartwheels on the runway, and I pictured the semi-truck being flipped over in Batman. And then I thought what the hell could have done that? Fishtailed makes more sense, thanks for the clarification.

There were a lot of reports like these that were complete assumption based on the fact that one witness said the airplane had flipped over. It actually hadn't.

I don't think airframes have quite the strength to flip end over end from contact with the ground, even at landing speeds. I can grab this pen rom my desk and throw it on the carpet so it flips vertically end over end. A 777 airframe might do something halfway between that and crumbling as it bounces.

Re: Armchair air crash investigator

#17

Post by momavujisic »

madiator wrote: post #12

Sorry to go offtopic here, but the images seem to be used without any credits. The first one was taken by David Eun ( https://path.com/p/1lwrZb )

I'm actually working right now to try to put some kind of overlay over the images for credit situations. My blog is still a WIP. Sorry!

Re: Armchair air crash investigator

#18

Post by jervisfm »

It goes without saying that my qualifications in aviation matters are only as an aviation enthusiast and for the full cause of the accident, we'll have to wait for the NTSB report (which has access to vital black box data and cockpit recordings).

However, I did give this accident some thought as well given the circumstances of the accident and came the pretty much the same final conclusion as the OP.

An airline pilot I once spoke to told me once that all the big jetliners use automated ILS with autopilot to automate the landings. The system is pretty accurate and reliable and can deliver landings as good as a well-trained and experienced pilot can.

When I saw the rather steep final approach the aircraft was making, I had suspected that the pilots were doing a manual landing. Now that we have information that the ILS was temporarily inoperational this appears to be what transpired and the pilots manually flew the final approach.

The precise reasons for why the manual approach ended up in this accident are still to be determined. One thing that I will point out though is that pilots for modern jetliners do relatively little actual manual flying of the plane. Modern airplanes have advanced FMS (Flight Management System) that allow for automatic flying from lift-off until landing with pilots overseeing the system. Given this lack of manual flying, there is a greater potential for human error when a pilot is required to actually do manual flying.

Re: Armchair air crash investigator

#19

Post by joezydeco »

pcl wrote: post #7
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...

Interesting. I wonder what the Asiana's descent profile looks like compared to the average and some outliers of other safe 777 landings at SFO. Did you generate that image? If not, what was the source?

From a reddit comment[1]:

"PPrune[2] also had a guy weighing in saying that when he flew for a Korean carrier he saw guys try to do banana-shaped approaches to get a smoother landing. Wouldn't be the first time the Koreans have pulled something like this."

[1] http://www.reddit.com/r/worldnews/comments/1hrewx/asiana_air...

[2] http://www.pprune.org

Re: Armchair air crash investigator

#20

Post by momavujisic »

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…

In a landing flare, you want to raise your negative V/S to near zero. A positive vertical speed means you're no longer descending, but ascending. Having a positive vertical speed during the landing flair is something you don't want to have as you're basically floating (and possibly climbing) above the runway and bleeding your airspeed which, in a couple seconds will most likely end in a hard landing as you've stalled while floating over the runway.

The positive rate of climb to me, indicates that they attempted to climb (go-around) but their low airspeed resulted in a stall.

It's important to remember that this data was pulled off Flightware which is basically aggregated data. and not from an accurate source such as the FDR. So my guess could be totally wrong.

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