Beta-Range lockout triggers?
Oh boy.. I can only take a shot at it. It sounds like you're talking about a turboprop's beta range. The beta range is the range of the propeller angle, that's near the flat pitch range. In this range, the prop will not (hardly) produce thrust and may even produce a little reverse thrust. Going even further back with the levers will get you into reverse (the prop blades turn to reverse pitch, thrusting the air forward).
Beta-range can only be used on the ground. Because the blades go to a flat pitch, the lateral air resistance imposed on the propeller is reduced to virtually zero. This could cause a dangerous runway prop overspeed, causing the propeller to separate (prop coming off or blades coming off, shooting through the cabin). This has happened in the past. If the prop would go further into reverse, that would be a very dangerous situation of course, possibly making the airplane uncontrollable.
So that's why there are locks that are activated when the plane leaves the ground, to prevent inadvertent beta-range selection in flight. The lowest possible power setting is flight idle. (Ground idle is in the beta range) Whenever the plane touches down, the lockout pins should be removed automatically, so reverse thrust can be set.
Specific lockout criteria vary per airplane probably. Hope this is the answer you're looking for!