As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED INSTRUMENT AIR PRESSURE WENT TO -0- IN FLIGHT, PILOT THEN SELECTED STANDBY PUMP AND RETURNED TO BASE. UP ON TROUBLESHOOTING THE MECHANIC REMOVED THE AIR PUMP AND FOUND THE SHAFT WAS SHEARED. NO PROBABLE CAUSE OR RECOMMENDATIONS AT THIS TIME. (K)