Reference Leadsleds post number 4, for what it’s worth, the Bristol Freighter did not have an Auto Feather System. It had an Auto Pitch Coarsening System. This worked by a comparison between air flows utilising two pitot tubes on each wing, one mounted within the propeller arc to detect the propeller airflow and one mounted at the wingtip in the free airflow.
The operation required the Master Auto Coarsening switch to be on, the Throttle levers to be at the marked Take Off position and the Propeller RPM levers to be fully forward, Should an engine fail during take-off, then reduction in the airflow within the propeller arc will reduce to something akin to the free airstream flow and result in no pressure differential between the pitot at the wingtip and the pitot behind the propeller arc. This would cause the propeller blades to be driven towards the coarse pitch position. Manual feathering from that position would then be required. Without Auto Coarsening being serviceable the aircraft was limited to a take-off weight of 40,000lb.