As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
D: PHX - AIR TURNBACK, APPROX 30 MIN AFTER TAKEOFF THE STANDBY HYDRAULIC LOW QUANTITY LIGHT ILLUMINATED, A AND B SYSTEM QUANTITY WAS NORMAL. THE AIRCRAFT RETURNED TO PHX. MAINTENANCE INSPECTED THE AIRCRAFT FOR LEAKS AND FOUND NONE. THE STANDBY HYDRAULIC RESEVOIR QUANTITY LOW LEVEL SWITCH WAS REPLACED AND TESTED NORMAL.