Navajo PA31-310 first year of manufacture 1967. Short coupled pitch stability problem solved by springs and bob weight to elevator. A very nice and docile machine, but no room left or expansion of the design.
The later versions Cheiftain, Mojave and Cheyennes just got worse. Up to the point that the British CAA refused to accept the certification data for the early Cheyennes and insisted on SAS as a no go item.
The then Pres ex FAA and some others were implicated in missing certification data and allegations it was fudged.
By then it was basically all over for the original Piper company.