I thought the criteria for this to operate the PTU was loss of Engine 1 (N2 Low) hence no EDP and flaps as per CaptsandL away from up and less than 15....and an autoslat demand due to hi AOA/low airspeed. PTU then runs extending slats fully. What am not sure of is will the PTU retract the slats after this....my understanding is not as they use different hydraulic lines to extend the slats and the PTU wont be running as the demand wont be there in the end as either the T/E flaps will be up or the auto slat demand wont be there? However am new to the 73CG (28 years 74!!) so am open to being told how it really works.... Have to agree the PTU probably never gets used except on maintenance checks or test flights (a good thing).
Fly safe...