Emergency: Solution ConfirmationOctober 10, 2017 in Canada ⋅ ⛅ 21 °C
This is intended to be the final wrapup. So it is in fact part 7 of 5. Since the last note I reported my test results and hypothesis for the failure to Pipistrel. On September 14 I had a phone call with the head of engineering. They were able to reproduce the failure scenario by following the same method I had.
They acknowledged that this is a real problem and are changing to a left hand thread as I proposed. They discovered that clearances are so tight that some bolts, although technically withing specification, but at the upper end of permissible tolerances can have some interference between the top of the rotating screw and the the stationary captive structure. That provides a screw loosening torque.
Presently they are going through the process with the Slovenian equivalent of the FAA to verifying the will eliminate the failure case. Then the applicable documentation and information dissemination will occur. This will include a change to their current manufacturing to use left hand threads as well as instructions for inspection for and replacement of existing interfering screws where found.