The back block release transmits motion from the actuator rod driver to the back-block latch, causing it to release.
The next picture shows the actuator back-block release installed on the control frame. The upper red (arity 3) connector of the stiffener of the rightmost actuator rod driver has been replaced with a yellow (arity 5) connector and blue strut. This blue strut will transmit the motion of the actuator rod driver through the back-block latch, disengaging it from the back-block lifter and allowing the actuator back-block to drop. This is how the control sequencing phase phase 4, to phase 5 of operation happens.
