In my line of business, I review various machinery vibration analysis reports. From my observations, most of the failures seem to be in front of the stab in the narrow fuselage section. There are a lot of factors that can affect fuselage failures. Resonance is one issue to be investigated. We know the YS four stroke engines have a different vibration pattern then the two stroke engines. The electrics seem to have relatively low vibration amplitudes. It would be nice to survey the failed planes and see if there is a common arrangement. Just my $0.02 worth.

Steve K.