As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THIS SWITCH IS THE CONTROL FOR THE POWER BRAKE PUMP. IT FAILS IN THE ELECTRICALLY 'OPEN' POSITION AND THE PUMP FAILS TO RUN CREATING A NO BRAKES CONDITION. SUBMITTER STATED IN LOOKING AT PAST RECORDS FOR THE LAST 5 YEARS, HAVE CHANGED THIS P/N SWITCH 5 TIMES IN FLEET OF 4 C-550'S. (CESSNA P/N 38-581-501).