Sounds as if they were heading in to rescue SOG personnel rigging nice little surprises along the Ho Chi Minh trail.
There was lots of that kind of activity going on but I suspect this crash happened during Operation Lam Son 719.
Timing is everything I guess. I left Pleiku on my first tour just before Tet of 68 and left I Corps on my second tour a couple of months before Lam Son 719.
http://a101avn.org/LamSon719.html
~huey driver.