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.
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...
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.
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.
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.
With a total of 273 fatalities, the disaster is the deadliest aviation accident to have occurred in the United States.(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 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.
Exactly what happened in this case; the airplane was built in 1991 to carry passengers, and then converted in 2006 for freight.
https://www.planespotters.net/airframe/mcdonnell-douglas-md-...