FLC RECEIVES TCASII RA ALERT WHILE DSNDING.

Narrative

DEPARTED PIT ENRTE TO BWI WITH AN FAA MAINT SAFETY INSPECTOR ON MY JUMP SEAT AS AN OBSERVER. SHORTLY AFTER TKOF; WE RECEIVED AN ECAM CAUTION REGARDING AN ENG #1 PROBE FAULT WITH NO FURTHER ECAM FOLLOW-UP REQUIREMENTS. I XFERRED CTL OF THE ACFT TO THE FO AND RESEARCHED THIS PROBE FAULT IN OUR ACFT HANDBOOK CHAPTER 21; TO VERIFY THAT THIS FAULT; WHILE IN THE AIR; IS FOR 'PLT AWARENESS ONLY;' NO FURTHER CREW ACTION REQUIRED. THIS PROBE FAULT ALSO CAUSED THE AFFECTED ENG (#1) TO SURGE BY INCREASING THEN DECREASING PWR OUTPUT; CAUSING THE ACFT TO YAW DUE TO THIS SURGE. AFTER DISCUSSION WITH MY FO AND THE FAA OBSERVER; I DETERMINED THAT THE SURGE DID NOT WARRANT A RETURN TO THE FIELD (PIT). THE THROTTLE LEVER ANGLE DONUT AND PWR LIMIT MARK WERE SURGING BTWN 90% AND 115% RANGE WITH ENG PWR TRYING TO FOLLOW. SINCE THESE INDICATORS ARE MAX LIMIT AND THE PWR REQUIREMENT WAS WELL BELOW THIS LEVEL; THE ENG NEVER SURGED MORE THAN 10-15% ABOVE OR BELOW ACTUAL REQUIREMENTS. THIS SCENARIO SETS THE STAGE FOR THE FOLLOWING EVENT: WHILE ON A DSCNT FROM APPROX 16000 FT TO ASSIGNED 10000 FT; WE RECEIVED A TA AT APPROX 13000 FT AT 10 O'CLOCK POS. THE VFR CESSNA WAS POSITIVELY IDENTED BY ME; MY FO AND THE FAA OBSERVER AS CLBING WITH A HIGH DECK ANGLE AT APPROX 2-3 MI; 400 FT BELOW US. WE WERE IN AN IDLE DSCNT AT APPROX 2500-3000 FPM DSCNT WITH THE #1 ENG STILL SURGING AT IDLE PWR. THE TA TURNED TO AN RA WITH A CLB REQUEST AT APPROX 300 FT VERT AND 1 MI HORIZ SEPARATION. THIS SCENARIO CALLS FOR MAX TOGA PWR AND MAX EFFORT CLB. CONSIDERING THE SURGING ENG (#1) AND THE POTENTIAL TO SURGE BEYOND 115% N1 AT MAX PWR AND THE VIOLENT ROLLING ACTION WHICH COULD FOLLOW IN A CLBING R TURN; I CHOSE TO CONTINUE THE DSCNT BECAUSE THE DSCNT RATE BTWN US WAS VERY RAPID AND THE TARGET ACFT (RA) WAS NOW TURNING TOWARDS US WHICH WOULD REMOVE HIM FROM OUR SIGHT. THIS EVENT WAS IN CLR VFR WITH THE TARGET ACFT NEVER OUT OF POSITIVE SIGHT TO ANYONE IN THE COCKPIT. AT NO TIME DID ATC CALL OUT THE TFC OR BRING IT TO OUR ATTN! VERY SHORTLY AFTER THE 'CLR OF CONFLICT;' ATC ISSUED A FREQ CHANGE BUT PRIOR TO LEAVING I ASKED ATC IF THEY WERE TALKING TO THIS ACFT AND DID THEY SEE IT. ATC SAID THEY SAW IT AND WERE NOT TALKING TO IT! I TOLD THEM OF THE RA EVENT AND CONTINUED TO BWI WITH NO FURTHER EVENTS.