As an ag pilot I deal with wires all the time. About 95% of the fields that I spray have wires either running through them, or are bordered on one or more sides by them.
Although people don't believe it, I have found that it is incredibly easy to simply 'forget' that the wires are there, even though I have crossed them countless times whilst spraying a field. When they blend in with the background it makes it even harder to deal with. The fact that they were on their third run leads me to believe that they may have simply forgot the wires were there, or they were looking at the main wires and forgot about the static line, as I have done on many occasions.
There but for grace of God go I.......a very sobering accident as we are getting ready to start our season in a week or so.