At the risk of extending a sidebar into a highjack, there is one thing you can do if you use AI like a search engine: verify the results yourself before publicly sharing them.
It’s interesting that it’s specific to the number 1 engine. Are the mount bearings different between #1 and #3 engine? And if not is there a flight characteristic that causes more stress on #1 engine?
It’s getting hard to tell what is and is not AI until a mistake is made in pronunciation or odd wording. It should be law that it is watermarked.
Where / how do you get the idea it’s specific to #1? And what exactly is the “it” you mean?
The specific pictures and diagrams they’re showing are #1, but that’s because that’s what’s relevant to this accident. There’s been verbiage, probably in the prelim report, than #3’s mounting is identical, net of some mirror imaging.
I can’t speak to #2; the rest of how it connects to the airplane is very different.
I never realized the engine pylon attached through a non-rigid mounting system (bearing).
I wonder what the design intention was. Because honestly, I would have thought a simple through-hole would be basically enough.
Torsional movement. It’s the reason wings flex in flight. Rigidity is not a good thing at 500 mph and 40,000 lbs of thrust. Imagine a thin knife blade that is bent slightly. The one with some give to it bends. the brittle one snaps in two.
From your cite upthread in post 9238:
But investigators found the same failure pattern on the McDonnell-Douglas-designed UPS MD-11’s No. 1 (left) engine bearing race, the report revealed.
I did not read the NTSB report, just the AP article. But this bit sounds fairly disturbing:
The last time those key engine mount parts were examined closely was in October 2021, and the plane wasn’t due for another detailed inspection for roughly 7,000 more takeoffs and landings.
I’m sure the full story is much more complicated and nuanced, but to this layman, that sounds like severely inadequate inspection frequency.
ISTM that the whole DC-10 family was nothing but trouble right from the start. The terrible DC-10 crash in Chicago in 1979 which was also caused by the #1 engine detaching had a different cause attributed to a maintenance error, but according to the AP article there was an ironic connection: the engine and pylon had been removed for inspection that included examining that fault-prone bearing. In that case it wasn’t the bearing failure that caused the engine to tear away, but improper handling of the pylon and engine assembly that produced a crack in the pylon.
Assuming 2 cycles per day (two take offs and landings which I’m assuming is reasonable for a UPS aircraft), 7000 cycles is about once a decade.
These guys fly a lot and constant inspections make it difficult to operate.
Obviously there’s more going on in this case and the inspection interval wasn’t appropriate, but as a target for this type of maintenance it’s reasonable when designing and certifying an aircraft. Methodologies for demonstrating the suitability of those intervals so have improved a lot over the years and regulations about aging aircraft are increasingly severe to try to bridge the gaps.
From a non-engineering prospective I never liked the results from the DC-10 event in Chicago. I always thought the attachment point should have been more robust to accommodate an engine replacement procedure. I understand the factory process wasn’t followed but it’s a big chunk of metal to hang and there’s always going to be some jockeying around to get it aligned.
The problem with airplanes is that they’re always engineered to be as light as possible. I’ve loaded 747-8’s that had no belly floors. Just the tracks for containers to roll on. It’s disconcerting to look down and see the wiring along the keel.
Sorry for the delayed response. My keyboard died on Friday and I’ve been limited to 2-sentence replies on my phone since. Now I’m back in my usual long-winded full keyboard mode.
Anyhow, I interpret that sentence as meaning the failure pattern was found on the #1 engine of the UPS MD-11. The one the #1 engine fell off of. Not that that pattern is limited to only occurring on #1 engines.
A bit higher in that same article there’s this bit:
In a mid-investigation update, the board revealed that a February 2011 Boeing service letter targeted the part, a bearing race that is part of the MD-11 engine-to-pylon mounting assembly, for repetitive inspections. The service letter detailed four failures of the part, which is part of a spherical bearing assembly, on three different airplanes.
If Boeing found 4 damaged bearings on 3 airplanes, clearly more than one engine location was involved. After all, on those 3 airplanes there’s a grand total of 3 #1 engines. The 4th bearing failure had to be on a #3 or possibly #2.
If AI can be accurate there are 3 spherical mounting bearings per wing mounted engine and 2 for the tail engine. But you may be right in that it’s the rear mounted bearing in question.
Based on investigations into the MD-11 engine mount systems, each of the two wing-mounted engines (No. 1 and No. 3) uses three primary spherical mounting bearings to connect the engine to the pylon
- Forward Mount: Contains two spherical bearings, vertically aligned (upper and lower).
- Aft Mount: Contains one spherical bearing housed within a two-lug assembly.
The investigation into the November 4, 2025, UPS MD-11F crash (Flight 2976) focused on the failure of this single, critical aft spherical bearing assembly on the left engine.
This makes me wonder if the modern 2 engine planes that produce more thrust will be prone to earlier failures rates. Imagine planes crabbing against a crosswind and then hitting the runway hard while the main gears yank the plane to runway alignment. That’s a lot of torsional load for an engine producing 110,000 lbs of thrust. That’s almost double an MD-11 engine.
This blogger talks about it and there’s a video of an engine showing slight movement to take up the load in place of a rigid mount.
That link doesn’t look like a real URL. It appears more like a snippet of the blog text with http:// in front of it.
By sad coincidence, MentourPilot’s video on Swissair 111 was released the same month as another Swiss tragic fire started by sparks igniting sub-par insulation:
Failures happen when designs are inadequately inadequate. Either loads are underestimated or materials are overestimated or defects occur in manufacture or damage unexpectedly accumulates in service or maintenance.
That’s true whether we’re talking about a Cox .049 glow plug engine mount or a GenX engine mount.
I wonder how many other people are doing this:
I’ll share this with my teen kid, who recently enjoyed the Spielberg-DiCaprio 2002 film Catch Me If You Can (mostly-true story of a fraudster who did the same thing, circa 1970).
(ETA: They mention the film at the end of the news piece.)