Thanks for posting that up... <cut>
Here's a quote of the "meat" of the whole document...
Interesting report. Thanks for posting that. I would summarize it differently (bottom).
Apparently, the re-manufacturer uses original 194x DUKW front axles (correct me if I am wrong) That's a 70y old part/ design. They also stretched the frame for more passenger capacity (increasing the load on the axle). Their customers drive them hard and experience a series of knuckle failures... The manufacturer is made aware and recommends immediate reinforcement (either a bottom tab gusset or a top and bottom half pipe gussets)... This was not always passed on or acted upon. The accident vehicle was 'patched' with a poorly welded tab gusset (bottom of the knuckle).
-I assume the axle was not removed for welding the tab. If so that's a rather tricky overhead weld (a curved surface too). That weld is in tension and not compression (weaker) making the quality of the weld important.
In my opinion the primary causes- weak 70y old axle design, not suitable for the task, knowing they are a problem, and having a bad welder fix it.
Another unrelated DUKW accident w/13 fatalities. Miss Majestic, Lake Hamilton in Hot Springs, Arkansas. The NTSB report. 2MB.pdf