Preliminary report has been posted on the NTSB site. Note that this is a report of what has been found SO FAR, and will probably be modified as the investigation proceeds.

^^^That was informative.

Any members A&Ps that could explain the procedure to lubricate those spherical bearings?

quote:

Originally posted by aileron:
It's been a very long time, but Iseem to recall AA using an unapproved maintenance procedure to raise and hold the engine in position while the pylon pins were inserted. Maybe a forklift was used? Anyway, the unauthorized procedure was either primary or contributing fault of AA 191 nearly 50 years ago.

It has indeed been a very long time and my (alleged) memory is not stellar, but as i recall they were lifting and installing the pylon and engine as a unit and removing it the same way (with a forklift in both cases). Perhaps given the big old long lever if it was jostled with the engine attached before all the pins attaching it to the wing were in the torque caused the damage which weakened the structure?

My recollection is that the recommended procedure was to attach the pylon to the wing, then attach the engine to the pylon when installing, and to remove the engine from the pylon, then remove the pylon from the wing when removing. Of course, given the alleged state of my memory, this could be all wrong…

^^^ This is what Juan in the above video was referencing.

quote:

Originally posted by trapper189:
^^^That was informative.

Any members A&Ps that could explain the procedure to lubricate those spherical bearings?

Remove access panel, use either a manual grease gun (like most people are familiar with) or battery powered.

Connect to a zerk fitting and pump until old grease is expelled and evidence of fresh grease is seen.

Wipe off excess, replace panel.

Pretty much how most items are greased.
Bolts and other items may be removed, disassembled, cleaned, inspected, lubed and reassembled per maintenance critria.

That sounds easy such that a misstep in the procedure itself seems unlikely to have exacerbated or caused the problem.

I wonder if the NTSB will be able to determine if the bearing had failed. I also wonder if it did fail, then will they be able to determine if it happened before or after it was greased, or if it was or wasn’t greased in Oct.

Presumably, the bearings are there to permit movement at that joint for a reason. I’m going to guess that reason is to prevent whatever stresses are on that joint from causing that joint to fail.

The part of this that failed, where the outer race of the spherical sits, isn't a point that should move. That should be a shrink fit where the alloy part is warmed enough that the steel spherical can be dropped into place. If that part is also steel, it would be pressed into place.
The greased area is around the outer part of the ball and the inner part of the outer race where the ball sits. Not the point where the bearing goes into that failed mount.
If there was a lubrication issue causing excessive wear in the spherical bearing, the forward thrust mount should also show signs and maybe even the front spherical bearings.
That failure point had a lot of hours on it and I'd suspect a likely some damage from maintenance (or less likely, a manufacturing defect) that caused a stress riser where the crack started.

^^^Understood. The video above has pictures from the NTSB showing the recovered bearing, races, and the broken parts that hold the races. I think the report mentioned the NTSB found fatigue fractures in the aft part that holds one of the bearing's races and bolts to the wing. If the bearing’s ability to move was restricted for some reason, would that not result in extra force being exerted on some other part potentially causing that part to fail?