It's hard to imagine any rewiring of plugs going on during a 2-hour turnround at JFK.

If that was the length of the time on the ground I would agree.

Aircraft being scrapped?

​​​​​​https://simpleflying.com/american-ai...rike-a321/amp/

Still no details what had happened? No interim report? Alas. They'll scrap the incident aircraft before we see analysis progress.

Fresh wing strike in pprune do that: 737-banged-up-papua

NTSB docket opened 6/14/22.

DCA19LA134

Opened a couple of months after the event in 2019; released to the public two days ago.

Unless I mixed the L/R sense on the data plot the crew's handling was as expected with resulting appropriate control surface movements.

What went wrong?

The CVR, the crew testimonies and crew interviews are shocking. They really had a near-death experience and even the ramp dude was amazed they made it back alive, after seeing the damage.
And this statement from the captain - still under the influence of the adrenaline rush - is something that Airbus will contest heavily.
(Well, at least they had the unexpected behavior on the yaw and roll axes, not on the pitch axis.)

I find the increasing left rudder pedal deflection (and control surface deflection) from 20:40.29 rather unusal, especially with the steady heading and the nose wheel still on the ground. (i.e., good view on the centerline).
I would expect the left rudder deflection for the crosswind from the right to be decreasing, but here it is increasing to its maximum left deflection (almost to the maximum available deflection) just about the nose gear leaving the ground.
I didn't feel the captain had a good recollection on what happened in those moments (aircraft unexpectedly veering left), and the F/O was not looking outside in those seconds.
The initial reflection of the captain was that the rudder pedal somehow "stuck" to the left, meaning that he wasn't aware of pushing it left, so either something or someone may have pushed it to the left, or the captain being under some sort of illusion of the airplane turning right, which he unknowlingly tried to complensate. Is there any centering force for the rudder pedals that may have become asymmetric?

More eyes, more detail, yes. https://data.ntsb.gov/Docket/Documen...9LA134-Rel.pdf

I did not realize which plot is the zero line on rudder trace - wrongly assumed the bold one which is 10 deg L, apparently. Now I note with interest the docket, among the usual files, has PDF entries on cross-wind take-off techniques.

Here's a pic with the zero rudder line enhanced:



https://cimg9.ibsrv.net/gimg/pprune....2bf4a2b8d1.jpg

The vertical orange line marks the moment of rudder zero position.

The green tick 20:40:35.25 marks peak pedal deflection at the "maximum recovery effort" moment. The pedals are hardwired connected, hence only one readout variable.
Same tick is superimposed at start-of-rolling-motion 20:40:32.25, suggesting there was a rudder input about 90% of physical travel - onside.

Still there's a more interesting moment.
from 20:40:31.25
until 20:40:31.75
When L-sidestick (PF) moves from centre to full R deflection in half a second. Strong hand right there, given the spring forces overcome. Is that a reaction to the developing track divergence (zero roll yet, still on the ground)? Wrong as it sounds, it could be - airplane veers to the donwind, we tilt the stick opposite direction. But watch the rudder - at that very moment the pedal deflection doubles into the downwind side.

Then sidestick is released for a second while the left rudder rudder is kept more than 50% of the travel into the roll.

Also took a look at the high res FDR plot

20:40:34 EDT shows WoW Sensor Main Right going to AIR. I will group some FDR evens around that timestamp. Values are read with sort of inaccuracy.

Rwy Mag HDG is 314°

-9 ... -4s:
Rudder between -0 and -10° (left), in sync with pedals

-4s ... -3s:
Rudder starts to exceed -10° (left)
Now HDG soon follows Rudder to left

-3 ..
Left Sidestick moved right 16° and pulled back 20°
Rudder quickly to -16° (left), then only gradually reduced
HDG changes up to 309°

-2s ...
Left Sidestick briefly moved to left -5° then right again 20°
Rudder only relieved to -13°
WoW Nose = Air
Roll (Bank) left up to -4°
HDG changes up to 301°

-1s ...
Right Sidestick had moved Right 20°
Rudder slowly reduced to -10° then runs right to 8° (note the pedal-to-rudder offset)
At time of WoW R Main = Air: Bank is -14° (left)

0s ...
Right Sidestick briefly released to <10° then again Right 20°
Left Sidestick briefly pushed to -3° then pulled again close to 20°
Right Sidestick follows the pull
HDG peaks at 290°
Bank develops to -36°
Rudder develops up to 20° right

+1s ...
Bank max at ~37°

+1.5s: WoW L Main = Air
then Rudder towards neutral
Both Sidesticks Lateral (Bank) towards neutral

+2s ...
Right Sidestick now is completly relased and not used anymore
Left Sidestick goes right then full left again
and is then reduced Longitudinal (Pitch) towards 0°
Rudder around neutral, then start to turn left again
bank reduces from -30 to -7°

+3s ...
Rudder at -20° (left) again
Bank around 0°
HDG 300°
Then Left Sidestick Lat (bank) back to 0°

+4s ...
Rudder back to neutral, then 2s right 10° then neutral for the remainder
Bank changes left to 16°
Left Sidestick moves right to 20°

+5s ...
Bank peaks at -20°
Now Left Sidestick is releived towards lat (bank) 4...0°
HDG ~288°

waito

You chose the reference zero at MLG RH WoW = Air understandably, that is when the bank which developed into the tip scrape begins.

Let me offer somewhat offset view. The ground contact was a terrifying ending of a problem. The bank angle is the second manifestation of the problem, the first being the centerline divergence. The problem is whatever caused that divergence. The dynamics of the banking motion and later ground contact are both in the consequences link of the accident chain.

At 20:40:31.5 the PF attempts a correction (quite wrongly), maybe becasue the aeroplane was observed pointing for a sideways excursion. An interesting moment when the onside rudder probably amplified the situation beyond controllable for this crew. Nevertheless, to my understanding, the 'chain-link zero timestamp' is 20:40:30.

Shame this was not a SE Asian LoCo or CEE ACMI P2F. By now we would be having a very livid discussion about the de-skilling of the pilot out of the profession with many well-researched academic explanations.

One more picture to show why I think 20:40:30 is relevant.

https://cimg1.ibsrv.net/gimg/pprune....8f885e7f3d.jpg

Notwithstanding the 5° symmetrical aileron droop, everyting is reading 0 except the rudder pedal and the (consistent) surface deflection. Initially needed to keep centeline under crosswind conditions, however at 20:40:30 the airplane starts deviating left. The rudder angle being steady until that point (cropped out), this could be due to increased aerodynamical effectiveness as the airpseed builds up (155 KIAS should be enought to be well airborne even for a heavy A321 BTW, what Vspeeds did they actually calculate?).

That heading deviation is followed by an additional L rudder pedal input while everything else remains perfectly neutral. That is the problem - I don't know what it is but I can see where it is.

Quack :sad:.

FlightDetent: My reference point "0 seconds" doesn't hold any importance. It's just meant as a split between takeoff roll and liftoff for orientation. As you show, the issue starts around 4 seconds before that. Why the rudder was moving this way I don't judge. I haven't read most of the files yet.

An interesting note from me for casual readers:

Wind from clearance was 010/17
A321 has a 25° sweepback wing
The heading change was up to 8° per second

When a swept wing plane is yawing left:
right wing accelerates forward into the wind = lift increase
right wing sweep angle reduces relative to airstream (160kn IAS vs. 010/17) = lift increase
left wing vice versa: ... decelerates ... sweep angle increases out of the airstream = lift decrease
within fast left roll, right wing effectivly faces lower AoA = lift decrease, left wing higher dynamic AoA, lift increase

Now I can't do the math obviously and what dominates over what. Let's not forget, countering aileron input was large. But just not enough obviously. By the way, what's the A321 Flight Law / Aileron Strategy in this takeoff phase?

Any mentioning of gusts in the docket? CVR states a 010/17G23 at landing clearence later.

Clear on that. A less understanding reader might focus on the wrong moment, hence I mentioned it.

Without checking the books, at this stage all control should be direct to the surfaces, no FBW magic. Apart from the relationship not being necessarily linear angle to angle that is, it could be electronically 'geared' but still with direct relation to control displacement.

Near full rudder will cause sideslip which comes with profound effect on the relative wing span (also shielding the root area on the leeway side). Guessing these two create the rolling motion the strongest, not any gusts. As you say, the rolling itself has a dampening effect but of a much smaller extent.

A conventional into-the-wind aileron input (not recorded on the trace btw, quack) prevents any undesired roll caused by gust on this dihedral wing. Very little is needed, around 3 deg - a piloting technique required to avoid raising the upwind spoilers.

In other words, as the QAR with a full set of data was immediately available most likely the knowledgeable people formed a very good understanding within 48 hours. Since then:
- no Airbus operational telex
- no bells from the ALPA

From the docket - bold is the accident minute at KJFK
https://cimg2.ibsrv.net/gimg/pprune....92345c340e.jpg

Follow up on the steering:

Ground mode is a direct relationship between sidestick deflection and elevator deflection, without auto trim. [FCOM DSC 27-20-10-20 A]

For roll control during take-off, the transition from Ground Mode blends into to Flight Mode (full FWB magic) over 0,5 seconds after the pitch reaches 8 degrees N.U. Thus anything afer 20:40:34 is roll demand control of the FBW - assuming it is what it actually does (pitch normal law is most certainly not a simple 1g command as the FCOM explains).

More observations:
+ despite full and dual R sidesticks, the aileron deflection is not maximized after Flight Mode becomes active. At 20:40:35 this is understandable, as the roll 1st derivation (not charted) peaks with reversal of the bank. Inbetween secon d 34-35 it is bit more confusing. Maybe the effect of absolute symmetrical deflection being reduced due to tkof aileron droop?
+ seconds 39-40 the aileron displacement is not symmetrical
+ we don't know the impact moment. Assuming it happened at recorded max bank is not correct.

That's interesting, how can someone find that moment actually? I looked for the ground impact moment as a sudden freeze or reduction of left bank angle, but I didn't find any. The wing damage is also more pronounced on the leading edge, i.e., hitting something sticking out of the ground. Maybe the left wingtip was only grazing the ground surface, without excerting a major force against the left roll.

Any thoughts about the rudder's transition from ground to flight mode?
As the captain reported that the rudder pedal felt "stiff" and had to input a larger than usual left rudder force with his left leg during the ground roll.
This makes me think that the pedals may have "softened up" during those few seconds, and this may have been another reason, why the captain inadvertendly increased the left pedal deflection.
He may have kept pusing the left pedal with the same force as during the ground roll, but the resistence of the pedal decreased unexpectedly, so the pedal deflection increased for a few seconds, before the captain could comprehend the situation and reverse the rudder.

I hope Airbus will not come with the same - and wrong - theory as Boeing did many years ago, when they claimed the pilots mixed up their left and right legs....

It might have been the max bank angle moment, just assuming automatically that is was is not correct.

Rudder has a direct linkage to flight deck and as such to my understanding only has a direct mode at all flight phases. FCOM is sketchy on this one and there is some witchcraft involving the (software) yaw damper. The yaw damper commands (also used for turn co-ordination) are NOT fed back to the pedals.

The personal profile of the S.I.C is not exactly the ordinary, not sure how common that is even in the US.
​​​​​​
For the moment I don't have an answer about the rudder pedals centering mechanism. However, unusual resistance is to be expected if you put unusual amount of it.

15 kts is the standard SIM cross-wind setup, should not be a new encounter to anyone. Reader beware, indeed, the tower reported wind only has a loose co-relation to the actual air mass environment experienced at rotation.

The plane did not strike the ground, God forbid. Only clipped the distance marker which is bad enough. Any such superstructure is frangible by regulation and the collision with 65-ish metric tonne behemoth at 160 knots hardly resulted in marked change in kinematics.

Audio? Not sure over the TKOF engine roar and it is easy to understand the crew had sensory overload just trying to process what they were seeing.