Oh woah, very insightful discussion thread you found there.
So the tl'dr is: the leading very preliminary theory is that the MD-11's left engine fell off the wing just like https://en.wikipedia.org/wiki/American_Airlines_Flight_191 (a DC-10, the immediate predecessor of the MD-11) which was caused by maintenance errors weakening the pylon structure holding the engine.
And just to add for those that aren't pilots: When they say "reduced airspeed to V2" that doesn't mean reducing engine power, it means pointing the nose higher while thrust remains at the maximum permissable setting. You're loosing speed but climbing faster.
This can happen if you accelerated past V2 (V2+20 is normal) before the engine failure and then after the failure you slow down to V2 to get the best climb angle on a single engine plus some safety margins above stall etc.
(asked earnestly out of lack of familiarity with this field) Are maintenance/certification standards distinct between passenger and cargo carriers?
It's hard for me to tell if this suggests a step backwards in application of the reforms instigated after AA191 or that those reforms were never copied over to cargo aviation.
Yes but mostly related to purpose specific things: passenger carriers have additional safety checks for cabin things like seats, oxygen and evacuation systems. Cargo carriers have additional safety checks for things like cargo restraint and decompression systems.
Furthermore (and I don't know if this is related to the cause of this crash), cargo jets tend to be older/refurbished passenger planes that have outlived their useful lives flying passengers.
To expand on #2, the loss of hydraulic pressure also caused the uncommanded retraction of the leading edge slats on the left wing, which was found by the NTSB to be part of the probable cause. Full report is here (PDF): https://www.ntsb.gov/investigations/AccidentReports/Reports/...
(I do not mean to imply that this exact slat retraction is necessarily relevant in the Louisville crash, however - I believe aircraft since AA191 are designed to maintain their wing configuration after loss of hydraulic pressure.)
This video from an aviation youtuber contains a picture of the engine: https://www.youtube.com/watch?v=U4q2ORhIQQc&t=526s (the video itself is also worth watching in full IMHO).
What strikes me as odd is that this looks like the "naked" engine, without the cowling/nacelle that usually surrounds it? Anyway, if an engine departs the aircraft shortly after (last-minute) maintenance was performed on it, that's indeed suspicious...
The cowling was probably easily torn off when the engine went full speed like a missile for a few seconds after detaching.
The parallels with AA Flight 191 are striking. In THAT accident it was found [1]:
1) improper maintenance—American Airlines had used a forklift shortcut to remove the engine and pylon together, rather than following McDonnell Douglas’s prescribed method
2) The detachment tore away part of the wing’s leading edge, rupturing hydraulic lines and severing electrical power to key systems, including the slat-position indicator and stall warning (stick shaker).
3) The pilots followed the standard engine-out procedure and reduced airspeed to V₂, which caused the aircraft to stall and roll uncontrollably left. This procedure was later found out to be incorrect.
Defective maintenance practices, inadequate oversight, vulnerabilities in DC-10 design, and unsafe training procedures combined to cause the crash, killing all 273 people on board and leading to sweeping reforms in airline maintenance and certification standards.
[1] https://www.youtube.com/watch?v=F6iU7Mmf330