AIRBUS EXPERIENCES UNCOMMANDED YAW ON COUPLED APCH TO MSP; MN.

Narrative

DURING ILS APCH; WITH BOTH AUTOPLT'S CONNECTED (COUPLED); SEVERAL UNUSUAL EVENTS WERE OBSERVED. 1) THE ACFT YAWED NOTICEABLY FOR NO APPARENT REASON. 2) THE AUTOLAND FAIL LIGHT ILLUMINATED (1500 FT) EVEN THOUGH IT SHOULD NEVER COME ON ABOVE 200 FT. 3) AUTOPLT #1 DISCONNECTED; WHICH IS NOT NORMAL; EVEN FOR AUTOLAND FAIL. 4) I RECALL SEEING A MOMENTARY ECAM MESSAGE ABOUT THRUST REVERSERS. I TOOK THE ACFT AND LANDED NORMALLY. MAINT INSPECTED THRUST REVERSERS -- NO FAULT NOTED. AFTER SOME DISCUSSION; THE WRITE-UP WAS SIGNED OFF. I REFUSED THE ACFT DUE TO LACK OF RESOLUTION OF THE UNCOMMANDED YAW AND AUTOLAND LIGHT AT INAPPROPRIATE ALT. A LATER REVIEW OF MAINT RECORDS SHOWED UNRESOLVED ISSUES WITH RADIO ALTIMETERS #1 AND #2; RUDDER LIMITER; THRUST REVERSER. READOUT FROM FLT DATA RECORDER INDICATES 5 DEG RUDDER DISPLACEMENT (UNCOMMANDED). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR INDICATED THAT THE ECAM THRUST REVERSER INDICATION WAS MOMENTARY AND THERE WERE NONE OF THE NORMAL REVERSE INDICATIONS DISPLAYED. THE YAW WAS FELT AND THE FLT DATA RECORDER INDICATED UNCOMMANDED RUDDER DISPLACEMENT AT THE TIME OF THE INCIDENT. THE ACFT WAS HELD OVER FOR MAINT FOR 6 HRS AND THE COMPANY UNION AND MANUFACTURER ARE LOOKING INTO THE INCIDENT. RPTR HAS FLOWN THE ACFT SINCE. THERE HAS BEEN A L ENG CHANGE AND NO FURTHER PROBS IN THE LOG HISTORY THAT HE HAS ACCESS TO.