AN A319 NOSEWHEEL STEERING DEVELOPED LARGE AMPLITUDE L AND R MOTIONS AFTER LNDG ROLL ON A WET RWY. FLT CREW HAD THE ACFT TOWED TO THE GATE.

Narrative

AFTER AN UNEVENTFUL LNDG ROLLOUT TO THE HIGH SPD TXWY; I TRANSITIONED LATERAL CTL OF THE ACFT FROM THE RUDDER PEDAL STEERING TO THE NOSEWHEEL TILLER. IT HAD BEEN RAINING AND THE FO AND I SAW SOME STANDING WATER ON THE TXWYS. THE FO NOTICED THAT IT FELT LIKE THE ACFT ANTISKID WAS 'WORKING' AS WE WENT THROUGH A SMALL PUDDLE BECAUSE INDEED THE SMALL BUMP THAT WE BOTH FELT IN THE SEAT OF OUR PANTS DID FEEL LIKE ANTISKID CYCLING. WHEN I STRAIGHTENED OUT THE ACFT ONTO THE PARALLEL TXWY AND RETURNED THE TILLER TO THE NEUTRAL POS; THE ACFT BEGAN JERKY UNCOMMANDED R AND L STEERING MOTIONS. IT WAS VERY SMALL AT FIRST AND WE THOUGHT MAYBE WE HAD BLOWN A TIRE. BUT AS I ROLLED FORWARD A LITTLE MORE I ASSESSED THAT THE NOSEWHEEL STEERING WAS THE PROB. I TAXIED FURTHER AND WE BOTH NOTICED THAT THE TRANSIENT UNCOMMANDED L AND R MOTION OF THE ACFT BECAME LARGER IN AMPLITUDE. IT WAS AT THAT TIME (AT THE ENTRANCE TO THE MIDFIELD RAMP FOR PARKING) THAT WE ELECTED TO STOP AND ASK FOR A TOW IN TO OUR GATE. WE ACCOMPLISHED THE TOW-IN CHKLIST.