I have discovered that both pilots were highly decorated VN vets. It is difficult to understand how such an accident could happen w/o an aircraft malfunction
It matters little how much experience a person has, being human all of us are capable of have a very, very bad day. LT COL Floyd B. Sweet was undergoing transition training and LT COL Kenneth T. Blank was his Flight Instructor. The accident was not unlike forgetting to put the gear down, except how many aircraft have wing sweep, so no experience or ingrained habit/muscle memory there to rely on.
https://aviation-safety.net/wikibase/wiki.php?id=152852
Blank had flown his 100th mission over North Vietnam with the 34 TFS in December 1966. By the time of his last F-105 flight in June 1967, he had accumulated 672 hours in the aircraft.
http://34tfsthuds.us/resources/Pictu..._Kenneth_T.pdf
What was LT COL. Sweet's Vietnam experience, could not find anything.