There were far too many problems with the TDX B747 operation to list them all - but you could start with an inept management team and inadequate maintenance. (examples provided upon request).
MIA based captains would literally cross their fingers on each departure in hopes that nothing would happen [Some actual events: loss of all instruments and all INSs, engine failures and shutdowns, air turnbacks, rejected takeoffs, fire warnings without fire bottles available, rudder malfunctions that were deferred for months, planes and crews held/delayed on numerous occasions for lack of permits...shall i continue?]
The Medellin accident hung the crew out to dry...but the ENTIRE company from the top down contributed to that accident. Supposedly they are getting one classic in MIA again. Hope it works out better for them this time around.