LEAK OF HYD FLUID ONTO APU COOLING INTAKE CAUSES SMOKE; NEAR EVAC.

Narrative

ON TAXI OUT FOR TKOF FROM MEM; THE #3 ENG WAS BEING STARTED AS THE ACFT WAS TURNING THE CORNER UP TO THE HOLD SHORT LINE. AS THE TURN WAS INITIATED; NOSEWHEEL STEERING WAS LOST. THE ACFT WAS STOPPED; PARKING BRAKE SET AND THE ENG START WAS COMPLETED. AT THIS TIME; THE A SYS HYD ANNUNCIATOR LIGHTS ON THE FO PANEL WERE ILLUMINATED; AS WELL AS BOTH OF THE SO PANEL A SYS LOW PRESSURE LIGHTS; WITH A SYS HYD QUANTITY 0 AND PRESSURE 0. AT THIS TIME; WE NOTICED SMOKE BLOWING FROM THE R PORTION OF THE ACFT FORWARD PAST THE NOSE. WE CALLED GND CTL WHO CONFIRMED THAT THERE WAS A SUBSTANTIAL AMOUNT OF SMOKE COMING OFF THE R WING. WE REQUESTED CRASH CREW ASSISTANCE AND TOLD GND WE MIGHT HAVE TO EVAC THE ACFT. I NOTIFIED THE FLT ATTENDANT IN CHARGE TO HAVE THE OTHER FLT ATTENDANTS PREPARE FOR POSSIBLE EMER EVAC. THE PAX WERE INFORMED THAT WE WERE AWARE OF A PROBLEM AND WERE INVESTIGATING IT. THE SO WAS SENT BACK TO THE CABIN TO VISUALLY CHK THE SMOKE'S ORIGIN. THE CAPT AND FO COMPLETED THE EMER EVAC CHKLIST UP TO THE POINT OF INITIATING THE EVAC. WHEN THE APU FIRE HANDLE WAS PULLED AS PART OF THE EVAC CHKLIST; THE SMOKE STOPPED ALMOST IMMEDIATELY. AN EVAC WAS NOT INITIATED. THE CRASH CREW ARRIVED WITHIN 3 MINS OF NOTIFICATION; COMPANY MAINT CAME OUT; PINNED THE GEAR AND TOWED THE ACFT BACK TO THE GATE. THE PROBLEM WAS CAUSED BY A CRACKED FITTING ON THE LNDG GEAR CTL VALVE THAT DUMPED A SYS HYD FLUID ALMOST DIRECTLY INTO THE APU COOLING AIR INTAKE; CAUSING THE SMOKE. WE CAME AS CLOSE TO AN EVAC AS YOU CAN WITHOUT ACTUALLY DOING IT. AS CAPT I WAS TORN BTWN A FEAR OF ORDERING A POSSIBLY UNNECESSARY EVAC WITH POTENTIAL INJURIES TO PAX AND THE FEAR OF HESITATING TOO LONG WITH POSSIBLE DISASTROUS CONSEQUENCES. GOOD COORD WITH GND CTL; FLT ATTENDANTS BUT PARTICULARLY AMONG THE 3 COCKPIT CREWMEMBERS; ALONG WITH USE OF CHKLISTS AND ESTABLISHED PROCS RESULTED IN A SATISFACTORY RESOLUTION TO THE PROBLEM WITH NO INJURIES.