It must be rather frustrating for Pilatus to see how their PC-6 is being abused.
They even used to have a limitation in the POH that vertical dives are prohibited.
Presently the ‘only’ limitations are the placard: DO NOT REVERSE IN FLIGHT
and the flight manual limitation
*Positioning of the power lever below the idle stop in flight is prohibited. *
Such positioning may lead to loss of airplane control or may result in an engine overspeed condition and consequent loss of engine power.
That said. When participation during airshows we usually asked if we could use the space reserved for the helicopters to takeoff and land…