A Technical Analysis Part Deux
This post is my second technical review/ analysis, and it too is long- my apologies again. It builds on the first posted two evenings ago. I don’t know how to go back and find that one, but it would probably help you to read that one before this one if you haven’t already done so.
In that post I analyzed the failure of the fuselage in front of the frame just in front of the rear cabin doors, as well as the failures in the rear fuselage. Based on a more intensive review of the available data (Including the two horizontal stabilizers- which were not available to me earlier) I have the following additional observations to make:
1. The fuselage appears to have failed in front of the frame in two discrete sequences. A careful review of the rivetline along the entire plane of failure shows scalloping and clear failure under tension from the top of the cabin approximately halfway down the side of the fuselage- approximately to where the floor would be. (In other words: It was forcibly pulled apart.)
2. From there down the failures are a zipper type tear. The paint is no longer missing from the elongated sections, and between each rivet the failure is a straight line, from the rear (aft) of one rivet to the front (forward facing) edge of the next rivet.
From these observations I think it is safe to say that the fuselage initially failed due to unknown forces being applied in a downward direction aft of the failure point. After that (we’re talking just a few seconds or even less for this entire evolution) the fuselage basically just fell off the rear of the airplane, which was probably accentuated as the aircraft was tumbling nose down due to the loss of the tail surfaces.
So what force(s) caused the fuselage to fail?? I have no idea, nor does anyone else on this board, but there are a few suggestive things to look at.
1. The only thing aft of the failure point even potentially capable of exerting such force was the horizontal stabilizer.
2. The horizontal stabilizer appears to have failed in a similar catastrophic symmetrical fashion, and at least on the port side the rear hinge-pin remained intact on the HS and simply tore the mounting pin right through the attach point located on the airframe. This is very suggestive of an enormous application of bending force.
3. The port side HS shows more intact carbon fiber around the hinge and still present pin, which would be both expected given the reinforcement, but which is also suggestive of a tearing motion in a rearward direction, pulling the fibers apart longitudinally. Additionally the leading edge of the torque box for the HS shows more damage (significantly more) than the rear, indicating (possibly) that the failure was in a generally front to back direction.
3. The rear of the rudder was destroyed as well. This suggests that it may have been impacted by the departing HS.
4. The other indicative evidence currently available is already in my previous post.
So what caused the Horizontal Stabilizer to fail??
1. Flutter is unlikely as while flutter could have caused the structure to instantly fail it would not have applied the necessary forces to cause the fuselage failure as described above. Additionally the FDR would show the extreme deviations of the control surfaces, even if for only a few milliseconds.
2. In my previous post I suggested a failure of the HS causing it to slam to a 90 degree angle but have since revised that possibility to one more in line with a failure of the jackscrew mounting plate, or something more benign. Many photos have already shown this plate (or what appears to be this plate) bent upwards into the vertical stabilizer assembly. (Also possibly explaining the missing rudder…) But at that altitude and airspeed it would likely only take 15 or 20 degrees of instant pitch change to destroy the tail- and to separate the fuselage before separating from the airframe. (20 degrees of negative pitch would equate to an increase in negative lift more than four times greater than what was being provided before that instant in time.) I’m totally making these calcs up, but if the static amount of downward force before the failure was 1000Kg then the resultant of the failure would increase that nearly instantly to 4300Kg roughly at the chord of the HS. With a moment arm of 10m (total estimate) between the HS and the failure point that would result in a torque (twisting) force going from 10,000kg/m to 43,000Kg/m. That would, in any reasonable world, break pretty much anything. (Because I’m in the prehistoric US- here’s that same rough calc in English units: 2000Lb increasing to 8600Lb at the chord of the HS. 30 feet of lever gives the initial static force as 60,000 ft. pounds and the resultant force at the moment of failure as 258,000 ft. pounds.) The point of those really creative numbers is to show that no matter what the negative lift was being provided on the tail it wouldn’t take much to push it to astronomic levels at the point of the fuselage where it failed.
3. A failure as described above would make one hell of a big bang.
So to sum all this up:
1. The airplane lost control and crashed because the tail separated from the fuselage, leaving it completely uncontrollable and (likely) tumbling as it came apart.
2. The available evidence suggests strongly (very strongly) that the failure in the tail occurred prior to the failure of the fuselage and pressure hull.
3. The tail of the fuselage separated from the fuselage (nearly certainly) because something (unknown) happened aft of the point of failure that inflicted a significant amount of bending force (torque) on the airframe itself, causing the failure under tension of the upper fuselage, and the subsequent and consequent zipper failure on the lower half once the initial force had been dissipated- and the HS had departed the aircraft.
4. The aircraft tumbled, destroying the rear fuselage up to the rear of the wing torque box.
5. The tail section, minus the entire HS assembly and a good portion of the vertical stabilizer and rudder descended hull down (due to the remaining sliver of vertical stabilizer) until it impacted the ground.
Everything I have described here is possible, is indicated by the available evidence, and would adequately explain the immediate failure of the FDR and CVR as they were literally right next to the main point of initial failure.
As to what initiated the chain of events I literally have no idea. I’m still working through the available video- like many others, but for the moment I’m still waiting to be shown by the US and UK as to how a bomb in the lower compartment led to the chain of failures that the visible record indicates occurred.
My .02 as always,
dce