Note that the official NTSB Probable Cause has yet to be published.
"3.2 Probable Cause
The National Transportation Safety Board determines that the probable cause of this accident was National Airlines’ inadequate procedures for restraining special cargo loads, which resulted in the loadmaster’s improper restraint of the cargo, which moved aft and damaged hydraulic systems Nos. 1 and 2 and horizontal stabilizer drive mechanism components, rendering the airplane uncontrollable.
Contributing to the accident was the Federal Aviation Administration’s inadequate oversight of National Airlines’ handling of special cargo loads."
Final report link is here if not already in this thread.
http://www.ntsb.gov/investigations/A...ts/AAR1501.pdf