Mute point? Here, here!

Full marks to the FAA for the video. There is a faint chance that someone who knows what they are talking about may spot a point overlooked by the investigators. Note I did say someone who knows what they are talking about.

From the fact that it was the Sheriff being interviewed in the second clip, I think it's fair to conclude that it was the Sheriff that invited the reporter in, not the NTSB; it seems the NTSB do not have 'exclusive custody' of the wreckage.

It depends on the individual aircraft. On some of our old 767's, we used to have the Left ATC powered only by the 115Vac Left Main Bus and on the rest of the 767 fleet, it was powered by the 115Vac Left Main Bus with backup from one of the HMGs (Hydraulic Motor Generators). You would need to look at the wiring diagrams/schematics for that particular aircraft.

I don't think the FAA had much to do with it, the NTSB is an independent agency. But I agree, nicely done for those of us who are interested in the investigation.

I haven't spent much time in the forward stabilizer compartment, but your image seems to match the maintenance manual.


https://cimg3.ibsrv.net/gimg/pprune....dd1bc3227b.jpg
There is no mention of total jackscrew length or diameter in the manual, so it will be difficult to create scale diagrams of the assembly. The trim only moves the assembly 21.51 inches during control column trimming (less if the flaps are less than 5 units). i.e. from 0.25 units (full nose down) to 12.8 units (full nose up) with column switches. Maximum range of the stabilizer is 0~14.2 units. 2 units is neutral.

At full nose down (0.25 units), the top of the moving part (ballnut) is within an inch of the upper stop.

Wow... :eek:

Good find.

Positioning in the video looks "close to" neutral. Not close to either stop. Unless it jammed there (and neutral was not the trim needed) or the whole unit broke loose from its mounts, that seems to minimize the odds of a THS jackscrew problem. (But you just never know).

On another note - probably having no significance to the accident - I have tentatively ID'd the "biggest part found so far" (shown at 5:10 in the reporter's first walk-around video, post 362) as the bottom half of the left winglet, and its junction with the wing tip.

Tracker Video Analysis
 

This is an analysis of the video using the Tracker video analysis program. I used the wingspan to calibrate distance, set the x-axis along the aircraft's track, and used the starboard engine to track the motion. I had to interpolate some frames when the aircraft was hidden behind the tree so take the middle of the graph with a grain of salt. There were also repeated frames in the video for some reason. FWIW, this is the result. Analysis shows that the ROD appears to change from over 200 m/s to just over 100 m/s towards the end of the sequence. Another source of error is using the wingspan to calibrate because the aircraft is banked relative to the camera.
https://cimg1.ibsrv.net/gimg/pprune....a9f5770639.jpg

Dash34 - I take it your graph is inverted (i.e. the top right corner of the graph shows the bottom of the dive)?

Given that we know the flightpath angle was approaching -50°, a ROD of 200 m/s would resolve to a velocity of around 500 kts.

Hmmm.

Correct. The zero reference point was set at the tail of the aircraft in the first frame it was visible. The slope of this graph is ROD. Time is on the x-axis, displacement from the reference point on the y-axis.

dash34,
The video is grainy, and the branch is in the way too, but I think I am seing that the wings towards the end of the video is deflected significantly upwards, like in a very hard pull up at very high speed. Such an observation is in line with your suggestion that the ROD was decreasing significantly at the end of the video.

Thanks!
This is obviously the HS jack screw. It seems like it is at about position 2.5 or 3. So, close to neutral or slightly nose up.

In the photo, the jackscrew is resting on the actuator end and the broken-off stabilizer bracket. I don't think you can necessarily read too much into the position of the ballnut - if its threads had stripped and it was free to move up and down the screw then the photo could simply be showing how the assembly has been positioned on the floor.

On the other hand, we could be looking at a perfectly serviceable jackscrew. There just isn't enough definition in the photo to tell.

Based on that, looks to me like recovered part is in full nose down position. Am I missing something?

Appears the same way to me. Another case of runaway trim?

Are you overestimating the amount of travel the ballnut moves? I see about 6~8 inches of chrome above the ballnut (wild guess, not knowing the diameter of the screw). Subtract 1 inch to get the start point of 0.25 units. There is 21.51 inches of travel from here (to reach 12.8 units). That is 1.7 inches per unit. So, 5~7 inches (say 6) is 3.5 units from 0.25 units = 3.75 units. Neutral is 2 units, so 1.75 units nose up. I need a fellow engineer to check my numbers.

Pilot input required here. If you're flying straight and level with the flap setting required at 6000 feet (?), what's the average trim setting? (aka... how long is a piece of string).

If the Statement:

"At full nose down (0.25 units), the top of the moving part (ballnut) is within an inch of the upper stop."

is correct, then the photographed screwjack is 80 to 90% Nose Down.

(look at the length of screwjack extending below the ballnut to the lower stop).

Whether this was how it was recovered, or if all the threads were stripped, would reduce the significance of the photo.