Eyewitness News has learned that design limitations of a World War II-era Dakota plane made it unsafe to attempt to fly over the Drakensburg.
The South African National Defence Force (SANDF) confirmed that six crew and five passengers were killed when the plane went down on Wednesday.
The Dakota DC-3 C-47 plane left the Waterkloof Air Force Base in Pretoria, en route to Umtata in the Eastern Cape.
It was understood the plane encountered severe weather.
Aviation correspondent Guy Leitch said that the plane was upgraded significantly, although this particular Dakota was more than 70 years old.
But he added that the modifications did not overcome the plane's fundamental limitations.
"Its inability to fly over the weather, deal with icy conditions and a lack of pressurisation [might have led to the crash]," he said.
Leitch says a safe flying altitude over the Drakensburg was 14 000 feet, but the Dakota was limited to 12 000 feet.
Why did the crew take the risk? "We cannot speculate why," Leitch said.
The SANDF has appointed a board of inquiry to investigate the circumstances surrounding the crash.
The defence force has since released the names of the victims:
Major K Misrole
Captain ZM Smith
Sergeant BK Baloyi
Sergeant E Boes
Sergeant JM Mamabolo
Corporal L Mofokeng
Sergeant L Sobantu
Corporal NW Khomo
Corporal A Matlaila
Corporal MJ Mthomben
Lance Corporal NK Aphane