Oops YouTube of the month...

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3WE
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Oops YouTube of the month...

Postby 3WE » Mon Mar 01, 2021 1:50 am

NOT_NEAR TOTAL DISASTER!!!!!. But:

https://youtu.be/WSuhDeujEM0

Outsider, ass-hat pontification:

I guess the main thing I see is that the braking seems fairly calm. Was there any reverse?

I suppose the touchdown was a bit delayed, and given the ‘unusual’ FA announcement- was this an “emergency” landing where they knew something was wrong and an over run was a possibility,
Commercial Pilot, Vandelay Industries, Inc., Plant Nutrient Division.

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Gabriel
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Re: Oops YouTube of the month...

Postby Gabriel » Mon Mar 01, 2021 3:53 am

They touched down waaaaaaaaaaaaaayyyyyy too long.

The runway starts less than 200 ft from the road you can see at 0:10 ~0:11.
They touched down 16 seconds later (0:27) some 4400 ft down the runway and with some 2700 ft remaining.

Oh and it was raining and the runway was wet.

The fact that they barely overrun the runway at very slow speed after such a short roll indicates more than fairly calm breaking.
The fact that the firefighters seem to spray the wheels / brakes is also a hint (did you notice that your ling is the "part 1"?)

And clearly yes, there was reverse.

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3WE
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Re: Oops YouTube of the month...

Postby 3WE » Mon Mar 01, 2021 4:45 pm

The fact that they barely overrun the runway at very slow speed after such a short roll indicates more than fairly calm breaking.
The fact that the firefighters seem to spray the wheels / brakes is also a hint (did you notice that your ling is the "part 1"?)

And clearly yes, there was reverse.
A no win argument, BUT I rewatched it, and no real camera bobble for hard braking, no loud roar of reverse, and very few exclamations from the passengers except when they left the runway...and then mostly humorous..."ummm, we are on the grass".

Look, I'm sure they braked good and hard and used reverse (it's done on normal landings too)...but perhaps they were smooth about it here. (And minimal judgementalism... other than yeah, they floated a good bit).

Also, the strange cabin announcement- "we are on final approach"...."Ummm, yes you are...and a rather short final approach at that...There might have been something amiss.

I'll further speculate (with no basis) that maybe they landed a little fast.
Commercial Pilot, Vandelay Industries, Inc., Plant Nutrient Division.

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Gabriel
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Re: Oops YouTube of the month...

Postby Gabriel » Mon Mar 01, 2021 6:29 pm

Say that they touched down at 130 kts. Asuming a uniform acceleration it would require an acceleration of 0.25g or 5 knots per second to stop in the remaining 2700 ft, which they did, more or less.

Now, the acceleration was not uniform. The spoilers take a couple of seconds to fully deploy and put full weight on wheels (and hence obtain full braking traction), the reversers take even longer to arm and then spool up. For sure the accelerations was much slower at the beginning, and hence it was stronger "after the beginning", so they "lost" say 5 seconds at high speed and little breaking in which they would have consumed another 600 ft so now you have 2100 ft of runway left ad still doing say 120 kts (supposing that you braked at 2 knots per second these first 5 seconds). That would leave you needing to slow down at 0.3g or almost 6 kts per second for the remaining of the roll (note: if this came only from braking, that would require a mu -coefficient of friction- of 0.3 which can be quite in the limit for a wet runway).

And then, it is possible, as you said, that they didn't apply max braking in the beginning and only applied the 6,000,000 PSI once they had the "oh shit" moment when they saw the end of the runway approaching. But note that even if they had applied max braking from the start, they were already in a pretty precarious condition to say the least. I agree with you that the reversers don't sound as loud as I would have expected, but the brakes can have been at max and, you know, the antiskid will keep those 6 million PSI from being constantly applied to the brakes, especially in a wet runway. So the lack of evidencie of hard braking (lack of screams and camera bobbling) may be not because they were not braking as hard as they could, but because "as hard as they could" was just not that hard because the traction was just not there.

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3WE
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Re: Oops YouTube of the month...

Postby 3WE » Tue Mar 02, 2021 9:29 pm

Gabriel: blah blah 6000000 PSI blah blah
Yes. (Genuinely.)
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Gabriel
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Re: Oops YouTube of the month...

Postby Gabriel » Wed Mar 03, 2021 3:19 pm

Gabriel: blah blah 6000000 PSI blah blah
Yes. (Genuinely.)
Well, I guess the bottom line is.. perhaps they didn't use all the decelerating means as quickly and as fully as they could have, and if they didn't, perhaps maximum application of all of them as quickly as posible could have prevented the overrun. Or perhaps they did do all that they possibly could to stop and that was still not enough

But boy they landed way too long in a runway that was wet and not so long and they deserved the overrun.


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