That dark area in the sheared surface of the PTO shaft means there was a pre-existing stress corrosion crack in the shaft. It's been ready to fail for a while. P.S. - Laura you can tell Dad that your on-line Engineering Team has totally exonerated you in the failure of the PTO shaft!

I’m from a different country (UK) and spent my life in a different game (construction) but we were told never to encroach within 6 metres (20 foot) horizontally of power cables, particularly with metal equipment like ladders, scaffold’s, cranes, telescopic booms etc etc. It’s surprising how far those power lines can arc.

Laura, it was not your fault that the PTO shaft broke. The break does not appear to be a brittle fracture that could be caused by overloading such as say putting too much crop in the header. Instead, it appears to be a fatigue failure that propagated over a long period of time from an initial small area of defect or damage on the shaft. It was going to fail one day and today happened to be the day.

If you look at the circular cross section of the broken shaft at 7:49, the area between 12 o'clock and 2 o'clock is darker indicating that section failed a season ago or perhaps earlier. The origin of the failure appears to be at the root of a spline at 1 o'clock caused by a tiny bit of damage or manufacturing defect in the past. A more recent propagation of failure can be seen in the lighter coloured area above a line from 9 o'clock to 4 o'clock. The area below 9 o'clock to 4 o'clock is where, with now too little good metal remaining to take the load, the shaft finally and instaneously brittle fractured.