Comment by philip1209
20 hours ago
Originally explained on the blancolirio channel on YouTube -
The timing and manner of the break make a lot more intuitive sense when you consider that the engine is essentially a massive gyroscope. As the plane starts to rotate, the spinning engine resists changes to the direction of its spin axis, putting load on the cowling. When the cowling and mount fail, that angular momentum helps fling the engine toward the fuselage.
I think far simpler explanation is "the back part failed first and engine is making thrust so it just flipped over on now-hinge mounting
That's why it flipped upwards, but not why it flipped towards the body of the plane / to the right.
Yes, and that lateral movement is very important since the debris seems to have caused at least one other engine to the right to fail as well.
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Yup. That's exactly what experts said of American Airlines flight 191 which was basically the same engine mount, same failure. Engine flipping over the wing.
The failure of the pylon appears to be different. On AA 191, the pylon rear bulkhead cracked and came apart. In the case of UPS flight 2976, the pylon rear bulkhead looks to be in one piece, but the mounting lugs at the top of the rear bulkhead cracked.
Admiral Cloudberg has a great article on AA 191 that covers exactly what happened: https://admiralcloudberg.medium.com/rain-of-fire-falling-the...
Ironically, AA flight 191 could have been salvageable, because the engine detaching didn't start a fire. However, it led to loss of hydraulic pressure on that wing, which led to the flaps/slats retracting on just the left wing, which led to the plane becoming uncontrollable. After that accident, the DC-10 was retrofitted with hydraulic fuses to prevent something like this happening again. Unfortunately, that didn't help the UPS crew, because in their case, the detachment caused more damage to the wing...
American 191's engine mount failed because of improper maintenance. It remains to be seen whether this failure had the same cause or if it was something else, such as metal fatigue.
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Flipping backwards is what caused the engine to fly to the right and land to the right of the takeoff runway. The stills in the NTSB preliminary report clearly show the engine flying over the aircraft, to the right, and then heading straight down.
There might be some truth in that. But the report doesn't confirm that theory.
What theory? That the mount failed? Or the rotation of the engine in the photos going up and over the fuselage?
It seems like both are true, but doesn't necessarily prove WHY the mount failed.
Not an aviation expert at all, so take this with a grain of salt, but I think "the spinning engine resists changes to the direction of its spin axis" offers two important insights:
* why it failed at rotation (the first/only sudden change of direction under full throttle) rather than as soon as it was mounted onto the plane, while taxiing, as soon as they throttled up, mid-flight, or on landing. This is important because at rotation is the worst possible time for this failure: no ability to abort take-off, no ability to land safety under no or severely limited power, little time to react at all, full fuel. Knowing these failures are likely to manifest then stresses the importance of avoiding them.
* why it failed in such a way that it damaged the rest of the plane.
Not so much what was wrong with the mounting in the first place, if that's what you're asking. Presumably it was designed to withstand the forces of this moment and clearly has done so many times before.
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That the engine was flung into the fuselage due to gyroscopic forces.
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I'm presenting it "useful not true" - not an RCA.
This is a preliminary report. Its purpose is to present initial evidence/information.
The final reports are always much more comprehensive.
I assume such forces are calculated and added in when deciding hot thick to make those mounting brackets.
Yes, obviously; MD-11s aren't flinging engines off the wing every single takeoff. A 34 year old airframe may or may not actually match design strength, though.
Yep. Now do 3 decades of metal fatigue.
Did I understand the report correctly that the part was scheduled to be replaced in the future after a certain number of hours, it just hadn't hit the threshold yet ?
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Yes, but the point is that this moment of the takeoff is when a failure that's been waiting to happen is most likely both because of the thrust and the gyroscopic resistance.
Aluminum has limited loading cycles
I'd be very surprised to read that the aft lug that cracked (and the bearing it contained) were made of aluminum. They were almost certainly steel or Inconel.
Wouldn't that be true of all cast metal objects?
Or are some metals impervious?
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