On Wednesday, January 14, 2015 at 10:15:02 AM UTC-7, Andrew wrote:

Thanks for sharing this info. I imagine these cracks are present on many other Pawnee glider tugs without the knowledge of the operators...

No doubt. These are VERY old airplanes and maintenance requirements tend to rise exponentially with age. All steel tube airframes suffer rust, corrosion and fatigue with the lowest areas suffering most. If your AI doesn't know to check this, get another AI.

I once saw an old Piper (PA-20, I IIRC) siting in the weeds with its nose pointing higher than it should. It appeared the tubes forward of the tail wheel had failed from the weight of the parked airplane.