AN AIRBUS 320 WHILE TAXIING SLOWLY AND MAKING A RUDDER CHK CAPT PUSHED TILLER DISCONNECT SWITCH AND ACFT VEERED L THEN TO R STOPPING 6 FT FROM GRASS CAUSED BY THE CAPT'S TILLER DISCONNECT SWITCH FAILURE.

Narrative

WHILE TAXIING TO RWY 18R TPA DOING CTL CHK; PUSHED RUDDER DISCONNECT TO DO RUDDER AND ACFT STARTED VEERING TO L WITH DISCONNECT RELEASED AND FULL R RUDDER. APPLIED FULL BRAKING AND FINALLY PARKING BRAKE TO BRING ACFT TO FULL STOP ABOUT 6 FT INFO GRASS. CALLED OPS TO TUG ACFT BACK TO GATE. HAD BOTH BRAKE STEERING CTL UNIT CHANNEL 1 AND 2 FAULT ALONG WITH STEERING CTL FAULT. MAINT NOTICED THAT TOWING PIN REMOVED LEVER DOES NOT GO ALL THE WAY TO TAXI POS AND TALKED THIS OVER. THEY DIDN'T THINK THIS IS WHAT CAUSED PROB. WOULD LIKE TO KNOW IF THIS LEVER DOES NOT GO ALL THE WAY TO LOCKED POS IF IT AFFECTS ACFT AT ALL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT FORTUNATELY THE AIRPLANE WAS BEING TAXIED SLOWLY WHEN THE FLT CTLS WERE CHKED. DURING THE L RUDDER CHK WITH THE TILLER DISCONNECT SWITCH ACTIVATED THE ACFT VEERED L AND AS THE RUDDER WENT R; THE ACFT VEERED R; STOPPING 6 FT SHORT OF THE GRASS. THE RPTR STATED WITH NORMAL RUDDER INPUT TO THE NOSEWHEEL STEERING ALLOWS ABOUT 6 DEGS OF MOVEMENT IN THIS CHK THE RUDDER ADDED 75 DEGS OF NOSE GEAR STEERING. THE RPTR SAID IF THIS FAILURE OCCURRED AT A HIGHER RATE OF TAXI SPD THE ACFT WOULD HAVE EXITED THE TXWY AND MAY HAVE BEEN DAMAGED. THE RPTR STATED WITHIN 3 SECONDS OF THE EVENT THE ECAM WARNING DISPLAYED BRAKE AND NOSE STEERING FAULT. THE RPTR SAID MAINT REPLACED A BRAKE STEERING CTL UNIT WHICH DID NOT CORRECT THE FAULT WHEN TAXI TESTED. THE RPTR SAID THE CORRECTIVE ACTION WAS REPLACEMENT OF THE TILLER BOX ASSEMBLY. THE RPTR STATED THIS AIRPLANE WAS FAIRLY NEW WITH ONLY 65 HRS TOTAL TIME. CALLBACK CONVERSATION WITH RPTR ACN 507071 REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAPT WAS STEERING THE ACFT WITH THE TILLER AND DURING THE FLT CTL CHK WAS ACTIVATING THE TILLER DISCONNECT SWITCH LOCATED ON THE TILLER. THE RPTR SAID WHEN THE RUDDER SWUNG L; THE AIRPLANE TURNED ABOUT 75 DEGS L AND THEN FOLLOWED THE R RUDDER ABOUT 75 DEGS R STOPPING JUST SHORT OF THE TXWY GRASS. THE RPTR STATED THE FAULT WAS THE TILLER DISCONNECT SWITCH FAILED AND THE NOSEWHEEL STEERING WAS CONNECTED DURING THE CHK. THE RPTR SAID THE TILLER AND CTL BOX WAS REPLACED.