This read-only field reports the last APS event detected on the protect (backup) port of a SONET redundant pair, the counterpart to c64SonetAPSWorkPortStatus for the standby side of the protection scheme. An admin uses this to verify the protect port itself is healthy and ready to take over, since a protect port with its own recent fault event would mean the backup path isn't actually reliable if the working port were to fail. For example, if this reports a fault event on the protect port at the same time the working port is healthy, the admin knows the protection scheme currently has no working fallback despite the primary path being fine.