John,
The accident occurred toward the end of the second (and last) day in
shooting the commercial. The filming involved at least thirty
professionals at the airport location plus some very-expensive
equipment. The glider was the star of the commercial. Also, the
glider pilot was being paid a lot of money. These add up to a lot of
motivation to do the stunts.

I believe that "improper operation of the controls" probably took
place in that the pilot pulled up too sharply and broke the rope.
That being said, the tragic chain of events certainly began a few days
earlier when the pilot (a high-time CFIG) agreed to launch his glider
using a 230' rope on a 2500' runway with a plan to make a 180-degree
turn and land back on the runway.

I agree that the root-cause of the accident was the serious error in
"aeronautical decision making." In terms of hazardous thought
patterns, impulsivity, resignation and macho come to mind.

This accident has reminded me how easy it can be to put safety
concerns aside and how unforgiving aviation can be.

Mark