As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE HOLDING SECOND IN LINE FOR TAKEOFF, SMOKE BEGAN TO FILL THE CABIN AND COCKPIT. ADVISED GROUND CONTROL ACFT WAS GOING TO TAXI OFF TO RIGHT INTO THE HOLDING AREA DUE TO SMOKE IN THE AIRCRAFT. SHUTDOWN BOTH ENGINES, APU, AND SECURED THE AIRCRAFT. CLOSE EXAMINATION OF THE TAIL SECTION REVEALED HYDRAULIC FLUID LEAKING FROM THE LOWER SECTION OF THE RUDDER NEAR THE RUDDER PCU. THIS AREA IS JUST ABOVE THE APU COMPARTMENT.